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Essay title generator




Buy research papers online cheap macromolecules of the cell Home » CH105: Chapter 11 – Introduction to the Major Macromolecules. Considering Dual Enrollment? Need a Chemistry Tutor? Use Your Creativity to Make a Difference! Apply for the Maurice Undergraduate Competition. Is Study Abroad Right for You? Is Study Abroad Affordable? STEM OR AMP Summer Bridge Program. College Credit in High I cant do my uni essay all lifeforms on Earth, from the tiniest bacterium to the giant sperm whale, there are four major classes of organic macromolecules that are always found and are essential to life. These are the carbohydrates, lipids (or fats), proteins, and nucleic acids. All of the major macromolecule classes are similar, in that, they are large polymers that are assembled from small repeating monomer subunits. In Chapter 6, you were introduced to the polymers of life and their building block structures, as shown below in Essay rater 11.1. Recall that the monomer units for building the nucleic acids, DNA and RNA, are the nucleotide bases, whereas best history essay writing service monomers for proteins are amino acids, for carbohydrates are sugar residues, and for lipids are fatty acids or acetyl groups. This chapter will focus on an introduction to the structure and function of these macromolecules. You will find that the major macromolecules are held together by the same chemical linkages that you’ve been exploring in Chapters 9 and 10, and rely heavily on dehydration synthesis for their formation, and hydrolysis for their breakdown. Figure 11.1: The Molecular building blocks of life are made from organic compounds. The major building block of proteins cheap college essay writing called alpha amino acids. As their name implies they contain a carboxylic acid functional group and an amine functional group. The alpha designation is used to indicate that these two functional groups are separated from one another by one carbon group. In addition to the amine and the carboxylic acid, the alpha carbon is also attached to a hydrogen and one additional group that can vary in size and length. In the diagram below, this group is designated as an R-group. Within writing services organisms there are 20 amino acids used as protein building blocks. Pay someone to write my paper differ from one another only at the R-group postion. The basic structure essay for graduate school an amino acid is shown below: Figure 11.2 General Structure of an Alpha Amino Acid. Within cellular systems, proteins are linked together by a complex system of Essay title generator and proteins called the ribosome. Thus, as the amino acids are linked together to form a specific protein, they are placed within a very specific order that is dictated by the genetic information contained within the RNA. This specific ordering of amino acids is known as the protein’s primary sequence. The essay zone sequence of a protein is linked together using dehydration synthesis that combine the carboxylic acid of the upstream amino acid with the amine functional group of the downstream amino acid to form an amide linkage. Within protein structures, this amide linkage is known as the peptide bond. Subsequent amino acids will be added onto the carboxylic acid terminal of the growing protein. Thus, proteins are always synthesized in a directional manner starting with the amine and ending with the carboxylic acid tail. New amino acids are always added onto the carboxylic acid tail, never onto the amine of the first amino acid in the chain. In addition, because the R-groups can be quite bulky, they usually alternate on either side of the growing protein chain in the trans conformation. The cis conformation is only preferred with one specific amino acid known as proline. Figure 11.3 Formation of the Peptide Bond. The addition of two amino acids to form a peptide requires dehydration synthesis. Proteins are very large molecules containing many amino acid residues linked together in very specific order. Proteins range in size from 50 amino acids in length to the largest known protein containing 33,423 amino acids. Macromolecules with fewer than 50 amino acids are known as peptides. Figure 11.4 Peptides and Proteins are macromolecules built from long chains of amino acids joined together through amide linkages. The identity and function of a peptide or a protein is determined by the primary sequence of amino acids within its structure. There are a total of 20 alpha amino acids that are commonly incorporated into protein structures (Figure 11.5). Figure 11.5 Structure of the 20 Alpha Amino Acids used in Protein Synthesis. Due to the large pool of amino acids that can be incorporated at each position within the protein, there are billions of different possible protein combinations that can be used to create novel protein structures! For example, think about a tripeptide made from this amino acid pool. At each position there are 20 different options that can be incorporated. Thus, the total number of resulting tripeptides possible would be 20 X 20 X 20 or 20 3which equals 8,000 different tripeptide options! Essay 70 words think about how many options there would be for a small peptide containing 40 amino acids. There would be 20 40 options, or a mind boggling 1.09 X 10 52 potential sequence options! Each of these options would vary in the overall protein shape, as the nature of the amino acid side chains helps to determine the interaction of the protein with the other residues in the protein itself and with its surrounding environment. Thus, it is useful to learn a little bit about the general characteristics of the amino acid side chains. The different amino professional career goals essay side chains can be grouped into different classes based on their chemical properties (Figure 11.5). For example, some amino acid side chains only contain carbon and hydrogen and are thus, very nonpolar and hydrophobic. Others contain electronegative functional groups with oxygen or nitrogen and can form hydrogen bonds forming more polar interactions. Still others contain carboxylic acid functional groups and can act as acids or they contain amines and can act as bases, forming fully charged molecules. The character of the amino acids throughout the protein help the protein to fold and form its 3-dimentional structure. It is this 3-D shape that is required for the functional activity of the protein (ie. protein shape = protein function). For proteins found inside the watery environments of the cell, hydrophobic amino acids will often be found on the inside of the protein structure, whereas water-loving hydrophilic amino acids will be on the surface where they can hydrogen bond and interact with the water molecules. Proline is unique because it has the only R-group that forms a cyclic structure with the amine functional group in the main chain. This cyclization is what causes proline to adopt the cis conformation rather than the trans conformation within the backbone. This shift is structure will often mean that prolines are positions where bends or directional changes occur within the protein. Methionine is unique, in that it serves as the starting amino acid for almost all of the many thousands of lined paper bulk known in nature. Cysteines contain thiol functional groups and thus, can be oxidized with other cysteine residues to form disulfide bonds within the protein structure (Figure 11.6). Disulfide bridges add additional stability to the 3-D structure and are often required for correct protein folding and function (Figure 11.6). Figure 11.6 Disulfide Bonds. Disulfide bonds a essay about school formed between two cysteine residues within a peptide or protein sequence or between different peptide or protein chains. In the example above the two peptide chains that form the hormone insulin are depicted. Disulfide bridges between the two chains are required for the essayer doublier quelquun quon aime function of this hormone to regulate blood glucose levels. The primary structure of each protein leads to the unique folding pattern that is characteristic for that specific protein. Recall that this is the linear order of the amino acids as they are linked together in the protein chain (Figure 11.7). Figure 11.7 Primary protein structure is the linear sequence of amino acids. (credit: modification of work by National Human Genome Research Institute) Within each protein small regions may adopt specific folding patterns. These specific motifs or patterns are called secondary structure. Common secondary structural features include alpha helix and beta-pleated sheet (Figure 11.8). Within these structures, intramolecular interactions, especially hydrogen bonding between the backbone amine and carbonyl functional groups are critical to maintain 3-dimensional shape. Every helical turn in an alpha helix has write my essay nz amino acid residues. The R groups (the variant groups) of the polypeptide protrude out from the α -helix chain. In the β -pleated sheet, the “pleats” are formed by hydrogen bonding between atoms on the backbone of the polypeptide chain. The R groups are attached to the carbons and extend above and below the folds of the pleat. The pleated segments align parallel or antiparallel to each other, and hydrogen bonds form between the partially positive nitrogen atom in the amino group and the partially negative oxygen atom in the carbonyl group of the peptide backbone. The α -helix and β -pleated sheet structures are found in most proteins and they play an important structural role. Figure 11.8 Secondary Structural Features in Protein Structure. The alpha helix and beta-pleated sheet are common structural motifs found in most proteins. They are held together by hydrogen bonding between the amine and the carbonyl oxygen within the amino acid backbone. There were many trade routes throughout the ancient world. The most highly traveled and culturally significant of these essay title generator called the Silk Road. The Silk Road ran from the Chinese city of Chang’an all the way through India and into the Mediterranean and Egypt. The reason that the Silk road was so culturally significant was because of the great distance that it covered. Essentially the entire ancient world was connected by one trade route. Figure 11. 9 Silkworms. On the route many things were traded, including silk, spices, slaves, ideas, and gun powder. The silk road had an astounding effect on the creation of many societies. It was able to bring economic wealth into areas along the route, and new ideas traveled the distance and influence many things including art. An example of this is Buddhist art that was found in India. The painting has many western influences that can be identified in it, such as realistic musculature of the people being painted. Also, the trade of gun powder to the West helped influence warfare, and in turn shaped the modern world. The real reason the Silk Road was started though was for the product that it takes its name from: Silk. Figure 11.10 Land route in Red, Sea route in Blue. Silk was prized by the Kings and Queens of both European and Middle Eastern Society. The Silk showed that the rulers had power and wealth because the silk was not easy to come by, and therefore was definitely not cheap. Silk was first developed in China, and is made by harvesting the silk from the cocoons of the mulberry silkworm. The silk itself is called a natural protein fiber because it is composed of a pattern of amino acids in a secondary protein structure. The secondary structure of silk is the beta pleated sheet. The primary structure of silk contains the amino acids of glycine, alanine, serine, in specific repeating pattern. These three amino acids make up 90% of the protein in silk. The last 10% is comprised of the amino acids glutamic acid, valine, and aspartic acid. These amino acids are used as side chains and affect things such as argumentative essay 9th grade and strength. they also vary between various species. The beta pleated sheet of silk is connected by hydrogen bonds. The hydrogen bonds in the silk form beta pleated sheets rather than alpha helixes because of where the bonds occur. The hydrogen bonds go from the amide hydrogens on one protein chain to the corresponding carbonyl oxygen across the way on essay grabber examples other protein chain. This is in contrast to the alpha helix because in that structure the bonds go from the amide to the carbonyl oxygen, but they are not adjacent. The carbonyl oxygen is on the amino acid that is four residues before. Figure 11.11 Parallel and Antiparallel Beta-Pleated Sheets. Silk is a great example of the beta pleated sheet structure. The formation of this secondary structure in the silk protein allows it to have very strong tensile strength. Silk also helped to form one of the greatest trading routes in history, allowing for the exchange of ideas, products and cultures while advancing the societies that were involved. Silk contains both anti-parallel and parallel arrangements of beta sheets. Unlike the α helix, though, the side chains are squeezed rather close together in a pleated-sheet arrangement. In consequence very bulky side chains essay title generator the structure unstable. This explains why silk is composed almost entirely of glycine, u of h essay prompt, and serine, the three amino acids with the essay 3000 words side chains. Some species of silk worm produce varying amounts of bulky side chains, but these silks are not as prized as the mulberry silkworm (which has no bulky amino acid side chains) because the silk with bulky side chains is weaker and doesn’t have as much tensile strength. The complete 3-dimensional shape of the entire protein (or sum of all essay title generator secondary structures) is known as the tertiary structure of the protein and is a unique and defining feature for that protein (Figure 11.12). Primarily, the interactions among R groups creates the complex three-dimensional tertiary structure of a protein. The nature of the R groups found in the amino acids involved can counteract the formation of the hydrogen bonds described for standard secondary structures. For example, Essay 99 groups with like essayer cest dГ©jГ  rГ©ussir are repelled by each other and those with unlike charges are attracted to each other (ionic bonds). When protein folding takes place, the hydrophobic R groups of nonpolar amino acids lay in the interior of the protein, whereas the hydrophilic R groups lay on the outside. The former types of interactions are also known as hydrophobic interactions. Interaction between toefl essay help app side chains forms disulfide linkages in the presence of oxygen, the only covalent bond forming during protein folding. Figure 11.12 Tertiary Protein Structure. The tertiary structure of proteins is determined by a variety of chemical interactions. These include hydrophobic interactions, ionic bonding, hydrogen bonding and disulfide linkages. All of these interactions, weak and strong, determine the final three-dimensional shape of the protein. When a protein loses its three-dimensional shape, it is usually no longer be functional. In nature, some proteins are formed from several polypeptides, also known as subunits, and the interaction of these subunits forms the quaternary structure. Weak interactions between the subunits help to stabilize the overall structure. For example, insulin (a globular protein) has a combination of hydrogen bonds and disulfide bonds that cause it to be mostly clumped into a ball shape. Insulin starts out as write my marketing paper single polypeptide and loses some internal sequences during cellular processing that essay title generator two chains held together by disulfide linkages as shown in figure 11.6. Three of these structures are then grouped further forming an inactive hexamer (Figure 11.13). The hexamer form of insulin is a way for the body to store insulin in a stable and inactive conformation so that it is available for release and reactivation in the monomer form. Figure 11.13 The Insulin Hormone is a Good Example of Quaternary Structure. Insulin is produced and stored in the body as a hexamer (a unit of six insulin molecules), while the active form is the monomer. The hexamer is an inactive form with long-term stability, which serves as a way to keep the highly reactive insulin protected, yet readily available. The four levels of protein structure (primary, secondary, tertiary, and quaternary) are summarized in An essay is a type of 11.14. Figure 11.14 The four levels of protein structure can be observed in these illustrations. (credit: modification of work by National Human Genome Research Institute) Hydrolysis is the breakdown of the primary protein sequence by the addition of water to reform the individual amino acids monomer units. Figure 11.15 Hydrolysis of Proteins. In the hydrolysis reaction, water is added across the amide bond incorporating the -OH group with the carbonyl carbon and reforming the carboxylic acid. The hydrogen from the water reforms the amine. If the protein is subject to changes in temperature, pH, or exposure to chemicals, the protein structure may unfold, losing its shape without breaking down the primary sequence in what is known as denaturation (Figure 11.16). Denaturation is different from hydrolysis, in that the primary strcture of the protein is not affected. Denaturation is often reversible because the primary structure of the polypeptide is conserved in the process if the denaturing agent is removed, allowing the protein to refold and resume its function. Sometimes, however, denaturation is irreversible, leading to a permanent loss of function. One example of irreversible essay title generator denaturation is when an egg is fried. The albumin protein in the liquid egg white is denatured when placed in a 2 essays in 2 days pan. Note that not all proteins are denatured at high temperatures; for instance, bacteria that survive in hot springs have proteins that function at temperatures close to boiling. The stomach is also very acidic, has a low pH, and denatures proteins as part long essay help the digestion process; however, the digestive enzymes of the stomach retain their activity under these conditions. Figure 11.16 Protein Denaturation. Figure (1) depicts the correctly folded intact protein. Step (2) applies heat to the system that is above the threshold of maintaining the intramolecular protein interactions. Step (3) shows the unfolded or denatured protein. Colored regions in the denatured essay title generator correspond to the colored regions of the natively folded protein shown in (1). Protein folding is critical to its function. It was originally thought that the proteins themselves were responsible for the folding process. Only recently was it found that often they receive assistance in the essay breakdown process from protein helpers known as chaperones (or write my essay south park that associate with the target protein during the folding process. They act by preventing aggregation of polypeptides that make up the complete protein structure, and they disassociate from the protein once the target protein is folded. Proteins are involved in many cellular functions. Proteins can act as enzymes which enhance the rate of chemical reactions. In fact, 99% of enzymatic reactions within a cell are mediated by proteins. Thus, they are integral in the processes of building up or breaking down of cellular components. Proteins can also act as structural scaffolding within the cell, helping to maintain cellular shape. Proteins can also be involved in cellular signaling and communication, as well as the transport of molecules from one location to another. Under extreme circumstances such as starvation, proteins can also be essay title generator as an energy source within speedypaper prices cell. 1. What type of protein facilitates or accelerates chemical reactions? an enzyme a hormone a membrane transport protein a tRNA molecule. 2. What are the monomers that make up proteins called? amino acids chaperones disaccharides nucleotides. between the R group of one amino acid and the R group of the second between the carboxyl group of one amino acid and the amino group of the other between the 6 carbon of both amino acids between the nitrogen atoms of the amino groups in the amino acids. the primary structure the secondary structure the tertiary structure the quaternary structure. changes in pH high temperatures all of custom and culture essay above the addition of some chemicals. Different amino acids produce different order pizza essay based on the bonds formed between them. Differences in amino acids lead to the essay 2 october of proteins, which produces other functional proteins. Different amino acids cause rearrangements of amino acids to produce a functional protein. Differences in the amino acids cause post-translational modification of the protein, which reassembles to produce a essay 7th pay commission protein. The primary chain forms secondary α-helix and β-pleated sheets which fold onto each other forming the tertiary structure. The primary structure undergoes alternative splicing to form secondary structures, which fold on other protein chains to form tertiary structures. The primary structure forms secondary α-helix and β-pleated sheets. This further undergoes phosphorylation and acetylation to form the tertiary structure. The primary structure undergoes alternative splicing to form a secondary structure, and then disulfide bonds give way to tertiary structures. Lipids, also commonly known as fats, are composed primarily of carbon and hydrogen. Due to this, lipids are predominantly hydrophobic molecules that do not dissolve with water. Lipid molecules may also contain limited amounts of oxygen, nitrogen, sulfur, and phosphorous. Lipids serve numerous and diverse purposes in the structure and functions of organisms. They can be a source of nutrients, a storage form for carbon, energy-storage molecules, structural components of membranes, and involved in chemical signaling and communication. Lipids comprise a broad class of many chemically distinct compounds, the most common of which are discussed in this section. The fatty acids are lipids that contain long-chain hydrocarbons terminated with a carboxylic acid functional group. Because the long hydrocarbon chain, fatty acids are hydrophobic (“water fearing”) or nonpolar. Fatty acids with hydrocarbon chains that contain only single bonds are called saturated fatty acids because they have the greatest number of hydrogen atoms possible and are, therefore, “saturated” with hydrogen. Fatty acids with hydrocarbon chains containing at least one double bond are called unsaturated fatty acids because they have fewer hydrogen atoms. Saturated fatty acids have a straight, flexible carbon backbone, whereas unsaturated fatty acids have “kinks” in their carbon skeleton because each double bond causes a rigid bend of the carbon skeleton. These differences in saturated versus unsaturated fatty acid structure result in different properties for the corresponding lipids in which the fatty acids are incorporated. For example, lipids containing saturated fatty acids are solids at room temperature, whereas lipids containing unsaturated fatty acids are liquids. A triacylglycerol, or triglyceride, is formed when three fatty acids are chemically linked to a glycerol molecule (Figure). Triglycerides are the primary components of adipose tissue (body fat), and are major constituents of sebum (skin oils). They play an important metabolic role, serving as efficient energy-storage molecules that can provide more than double the caloric content of both carbohydrates and proteins. Triglycerides are composed of a glycerol molecule attached to three fatty acids by a dehydration synthesis reaction. Explain why fatty acids with hydrocarbon chains that contain only single bonds are called saturated fatty acids. Triglycerides are classified as simple lipids because they are formed from just two types of compounds: glycerol and fatty acids. In contrast, complex lipids contain at least one additional component, essay writing service nottingham example, a phosphate group (phospholipid s ) or a carbohydrate moiety (glycolipid s ). Figure depicts a typical phospholipid composed of two fatty acids linked to glycerol (a diglyceride). The two fatty acid carbon chains may be both saturated, both unsaturated, or one of each. Instead of another fatty acid molecule (as for triglycerides), the third binding position on the glycerol molecule is occupied by a modified phosphate group. This illustration shows a phospholipid with two different fatty acids, one saturated and one unsaturated, bonded to the glycerol molecule. The unsaturated fatty acid has a slight kink in its structure due to the double bond. The molecular structure of lipids results in unique behavior in aqueous environments. Figure depicts the structure of a triglyceride. Because all three substituents on the glycerol backbone are long hydrocarbon chains, these compounds are nonpolar and not significantly attracted to polar water molecules—they are hydrophobic. Conversely, phospholipids such as the one shown in Figure have a negatively charged phosphate group. Because the phosphate is charged, it is capable of strong attraction to water molecules and thus is hydrophilic, or “water loving.” The essay knowledge is power portion of the phospholipid is often referred to as a polar “head,” and the long hydrocarbon chains as nonpolar “tails.” A molecule presenting a hydrophobic portion and a hydrophilic moiety is said to be amphipathic. Notice the “R” designation within the hydrophilic head depicted in Figure, indicating that a polar head group can be more complex than a simple phosphate moiety. Glycolipids are examples in which carbohydrates are bonded to the lipids’ head groups. The amphipathic nature of phospholipids enables them to form uniquely functional structures in aqueous environments. As mentioned, the polar heads of these molecules are strongly attracted to water molecules, and the nonpolar tails are not. Because of their considerable lengths, these tails are, in fact, strongly attracted to one another. E-commerce essay topics a result, energetically stable, large-scale assemblies of phospholipid molecules are formed in which the hydrophobic tails congregate within enclosed regions, shielded from contact with water by the polar heads (Figure). The simplest of these structures are micelle sspherical assemblies containing a hydrophobic interior of phospholipid tails and an outer surface of polar head groups. Larger and more complex structures are created from lipid-bilayer sheets, or unit membranes, which are large, two-dimensional assemblies of phospholipids congregated tail to tail. The cell essay title generator of nearly all organisms are made from lipid-bilayer sheets, as are the membranes of many intracellular components. These sheets may also form lipid-bilayer spheres that are the structural basis of vesicles and liposomes, subcellular components that play a role in numerous physiological functions. Phospholipids tend to arrange themselves in aqueous solution forming liposomes, micelles, or lipid bilayer sheets. (credit: modification of work by Mariana Ruiz Villarreal) How is the amphipathic nature of phospholipids significant? The isoprenoids are branched lipids, also referred to as terpenoids, that are formed by chemical modifications of the isoprene molecule (Figure). These lipids play a wide variety of physiological roles in plants and animals, with many technological uses as pharmaceuticals (capsaicin), pigments (e.g., orange beta carotene, xanthophylls), and fragrances (e.g., menthol, camphor, limonene [lemon fragrance], and pinene [pine fragrance]). Long-chain isoprenoids are also found in hydrophobic oils and waxes. Waxes are typically water resistant and hard at room temperature, but they soften when heated and liquefy if warmed adequately. In humans, the main wax production occurs within the sebaceous glands of hair follicles in the skin, resulting in a secreted material called sebum, which consists mainly of triacylglycerol, wax esters, and the hydrocarbon squalene. There are many bacteria in the microbiota on the skin that feed on these lipids. One of the most prominent bacteria that feed on lipids is Propionibacterium acneswhich uses the skin’s lipids to generate short-chain fatty acids and is involved in the production of acne. Five-carbon isoprene molecules are chemically modified in various ways to yield isoprenoids. Another type of lipids are steroid scomplex, ringed structures that are found in cell membranes; some function as hormones. The most common types of steroids are sterol swhich are steroids containing an OH group. These do my law essay mainly hydrophobic molecules, but also have hydrophilic hydroxyl groups. The most common sterol found in animal tissues is cholesterol. Its structure buying term paper of four rings with a double bond in one of the rings, and a hydroxyl group at the sterol-defining position. The function of cholesterol is to strengthen cell membranes in eukaryotes and in bacteria without cell walls, such as Mycoplasma. Prokaryotes generally do not produce cholesterol, although bacteria produce similar compounds called hopanoids, which are also multiringed structures that strengthen bacterial membranes (Figure). Fungi and some write my essay for me free online produce a similar compound called ergosterol, which strengthens the cell membranes of these organisms. Cholesterol and hopene (a hopanoid compound) are molecules that reinforce the structure of the cell membranes in eukaryotes and prokaryotes, respectively. This video provides additional information about phospholipids and liposomes. How are isoprenoids used in technology? The moisturizing essay 0n environment prescribed by Penny’s doctor was a topical corticosteroid cream containing hydrocortisone. Hydrocortisone is a synthetic form of cortisol, a corticosteroid hormone produced in the adrenal glands, from cholesterol. When applied directly to the skin, it can reduce inflammation and temporarily relieve minor skin irritations, itching, and rashes by reducing the secretion of histamine, a compound produced by cells of the immune system in response to the presence of pathogens or other foreign substances. Because histamine triggers the body’s inflammatory response, the ability of hydrocortisone to reduce the local production of histamine in the skin effectively suppresses the immune system and helps limit inflammation and accompanying symptoms such as pruritus (itching) and rashes. Does the corticosteroid cream treat the cause of Penny’s rash, or just the symptoms? Jump to the next Clinical Focus box. Go back to the previous Clinical Focus box. Lipids are composed mainly of carbon and hydrogen, but they can also contain oxygen, nitrogen, sulfur, and phosphorous. They provide nutrients for organisms, store carbon and energy, play structural roles in membranes, and function as hormones, pharmaceuticals, fragrances, and pigments. Fatty acids are long-chain hydrocarbons with a carboxylic acid functional group. Their relatively long nonpolar hydrocarbon chains make them hydrophobic. Fatty acids with no double bonds are saturated ; those with double bonds are unsaturated. Fatty acids chemically bond to glycerol to form structurally essential lipids such as triglycerides f.r. leavis essay on keats pdf phospholipids. Triglycerides comprise three fatty acids bonded to glycerol, yielding a hydrophobic molecule. Phospholipids contain both hydrophobic hydrocarbon chains and polar head groups, making the skin i m in essay amphipathic and capable of forming uniquely functional large scale structures. Biological membranes are large-scale structures based on phospholipid bilayers that provide hydrophilic exterior and interior surfaces suitable for aqueous environments, separated by an intervening hydrophobic layer. These bilayers are the structural basis for cell membranes in most organisms, as well as subcellular components such as vesicles. Isoprenoids are lipids derived from isoprene molecules that essay title generator many physiological roles and a variety of commercial applications. A wax is a long-chain isoprenoid that is typically essay 600 words example resistant; an example of a wax-containing substance is sebum, produced by sebaceous glands in the skin. Steroids are lipids with complex, ringed structures that function as structural components of cell membranes and as hormones. Sterols are a subclass of steroids containing a hydroxyl group at a specific location on one of the molecule’s rings; one example is cholesterol. Bacteria produce hopanoids, structurally similar to cholesterol, to strengthen bacterial membranes. Fungi and protozoa produce a strengthening agent called ergosterol. Which of the following describes lipids? A. a source of nutrients for organisms B. energy-storage molecules C. molecules having structural role in membranes D. molecules that are part of hormones and pigments E. all of the above. Molecules bearing both polar and nonpolar groups are said to be which of the following? A. hydrophilic B. amphipathic C. hydrophobic D. polyfunctional. Lipids are a naturally occurring group of substances that are not soluble in water but are freely soluble in organic solvents. Fatty acids having no double bonds are called essay help in triglyceride is formed by joining three glycerol molecules to a fatty acid backbone in a dehydration reaction. Waxes essays r easy esters formed from long-chain __________ and saturated __________, and they may also contain substituted hydrocarbons. alcohols; fatty acids. Cholesterol is the most common member of the __________ group, found in animal tissues; it has a tetracyclic carbon ring system with a __________ bond in one of the rings and one free __________group. steroid; double; hydroxyl. Microorganisms can thrive under many different conditions, including high-temperature environments such as hot springs. To function properly, cell membranes have to be in a fluid state. How do you expect the india custom essay acid content (saturated versus unsaturated) of bacteria living in high-temperature environments might compare with that of bacteria living in more moderate temperatures? Describe the structure of a typical phospholipid. Are these molecules polar or nonpolar? The formulas of many carbohydrates can be written essay jewelry carbon hydrates, C n (H 2 O) nhence their name. The carbohydrates are a major source of metabolic energy, both for plants and for animals that depend on plants for food. Aside from the sugars and starches that meet this vital nutritional role, carbohydrates also serve as a structural material (cellulose), a component of the energy transport compound ATP, recognition sites on cell surfaces, and one of three essential components of DNA and RNA. Carbohydrates are called saccharides or, if they are relatively small, sugars. Several classifications of carbohydrates have proven useful, and are outlined in the following table. Carbohydrates have been given non-systematic names, although the suffix ose is generally used. The most common carbohydrate is glucose (C 6 H 12 O 6 ). Applying the custom essay papers writing service defined above, glucose is a monosaccharide, an aldohexose (note that the function and size classifications are combined in one word) and a reducing sugar. The general structure of glucose and many other aldohexoses was established by simple chemical reactions. The following diagram illustrates the kind of evidence considered, although some of the reagents shown here are different from those used by the original scientists. Hot hydriodic acid (HI) was often used to reductively remove oxygen functional groups from a molecule, and in write a 1 2 page essay wherein you consider the effectiveness of the international labor organizatio case of glucose this treatment gave hexane (in low yield). From this it which online store research paper for sale is better concluded that the six carbons are in an unbranched chain. The presence of an aldehyde carbonyl group was deduced from cyanohydrin formation, its reduction to the hexa-alcohol sorbitol, also called glucitol, and mild oxidation to the mono-carboxylic acid, glucuronic acid. Somewhat stronger oxidation by dilute nitric acid gave the diacid, glucaric acid, supporting the proposal of a six-carbon chain. The five oxygens remaining in glucose after the aldehyde was accounted for were thought to be in hydroxyl groups, since a penta-acetate derivative could be made. These hydroxyl groups were assigned, one each, to the last five carbon atoms, because essay title generator hydroxyl groups are normally unstable relative to the carbonyl compound formed by loss of water. By clicking on the above diagramit will change to display the suggested products and the gross structure of glucose. The four middle carbon atoms in the glucose chain are centers of chirality and are colored red. Glucose and other saccharides are extensively cleaved by periodic acid, thanks to the abundance of vicinal diol moieties in their structure. This oxidative cleavage, do i underline my essay title as the Malaprade reaction is particularly useful for the analysis of selective O-substituted derivatives of saccharides, since ether functions do not react. The stoichiometry of aldohexose cleavage is shown in the following equation. The four chiral centers in glucose indicate there may be as many as sixteen (2 4 ) stereoisomers having this constitution. These would exist as eight diastereomeric pairs of enantiomers, and the initial challenge was to determine which of the eight corresponded to glucose. This challenge was accepted and met in 1891 essay 100 the German chemist Emil Fischer. His successful negotiation of the stereochemical maze presented by the aldohexoses was a logical tour de force, and it is fitting that he received the 1902 Nobel Prize for chemistry for 6$ essay review accomplishment. One of the first tasks faced by Fischer was to devise a method of representing the configuration of each chiral center in an unambiguous manner. To this end, he invented a simple technique for drawing chains of chiral centers, that we now essay title generator the Fischer projection formula. Click on this link for a review. At the time Fischer undertook the glucose project it was not possible to establish the absolute configuration of an enantiomer. Essay help me, Fischer made an arbitrary choice for (+)-glucose and established a network of related aldose configurations that he called the D -family. The mirror images of these configurations were then designated the L -family of aldoses. To illustrate using present day knowledge, Fischer projection formulas and names for the D-aldose essay typer unblocked (three to six-carbon atoms) are shown below, with the asymmetric carbon atoms (chiral centers) colored red. The last chiral center in an aldose chain (farthest from the aldehyde group) was chosen by Fischer as the D / L designator site. If the hydroxyl group in the projection formula pointed to the right, it was defined as a member of the D-family. A left directed hydroxyl group (the mirror image) then represented the L-family. Fischer’s initial assignment of the D-configuration had a 50:50 chance of being right, but all his subsequent essay knowledge is power concerning the relative configurations of various aldoses were soundly based. In 1951 x-ray fluorescence studies of (+)-tartaric acid, carried out in the Netherlands by Johannes Martin Bijvoet (pronounced “buy foot”), proved that Fischer’s choice was correct . It is important to recognize that the sign of a compound’s specific rotation (an experimental number) does not correlate with its configuration (D or L). It is a simple matter to measure an optical rotation with a polarimeter. Determining an absolute configuration usually requires chemical interconversion with known compounds by stereospecific reaction paths. Models 4 paragraph essay graphic organizer pdf representative aldoses may be examined by clicking on the Fischer formulas for glyceraldehyde, erythrose, threose, ribose, arabinose, allose, altrose, glucose or mannose in the above diagram. Emil Fischer made use of several key reactions in the course of his carbohydrate studies. These are described here, together with the information that each delivers. As noted above, sugars may be classified as reducing or non-reducing based on their reactivity with Tollens’, Benedict’s or Fehling’s reagents. If a sugar is oxidized by these reagents it is called reducingsince the oxidant (Ag (+) or Cu (+2) ) is reduced in the reaction, as evidenced by formation of a silver mirror or precipitation of cuprous oxide. The Tollens’ test is commonly used to detect aldehyde functions; and because of the facile interconversion of ketoses and aldoses under the basic conditions of this test, ketoses such essay c apply texas fructose also react and are classified as reducing sugars. When the aldehyde function of an aldose is oxidized to a carboxylic acid the product is called an aldonic acid. Because of the 2º hydroxyl functions that are also present in these compounds, a mild oxidizing agent such as hypobromite must be used for this conversion (equation 1). If both ends of an aldose chain are oxidized to carboxylic acids the product is called an aldaric acid. By converting an aldose to its corresponding aldaric acid derivative, the ends of the chain become identical (this could also be accomplished by reducing the aldehyde to CH 2 OH, as noted below). Such an operation will disclose any write essay on grow more trees symmetry in the remaining molecule. Thus, ribose, xylose, allose and galactose yield achiral aldaric acids which are, of course, not optically active. The ribose oxidation is shown in equation 2 below. Other aldose sugars may give identical chiral aldaric acid products, implying a unique configurational relationship. The examples of arabinose and lyxose shown in equation 3 above illustrate this result. Remember, a Fischer projection formula may be rotated by 180º in the plane of projection without changing its configuration. Sodium borohydride reduction of an aldose makes the ends dissertation essay help the resulting alditol chain identical, HOCH 2 (CHOH) n CH 2 OH, thereby accomplishing the same configurational change produced by oxidation to an aldaric acid. Thus, allitol and galactitol from reduction of allose and galactose are achiral, and altrose and talose are reduced to the same chiral alditol. A summary of these redox reactions, and derivative nomenclature is given in the following table. If a monosaccharide has a carbonyl function on one of the inner atoms of the carbon chain it is classified as a ketose. Dihydroxyacetone may not be a sugar, but it is included as the ketose analog of glyceraldehyde. The carbonyl pay for someone to write my essay is commonly found at C-2, as illustrated by the following examples (chiral centers are colored red). As expected, the carbonyl function of a ketose may be reduced by sodium borohydride, usually to a mixture of epimeric products. D-Fructose, the sweetest of the common natural sugars, is for example reduced to a mixture of D-glucitol (sorbitol) and D-mannitol, named after the aldohexoses from which they may also be obtained by analogous reduction. Mannitol is itself a common natural carbohydrate. Although the ketoses are distinct isomers of the aldose monosaccharides, the chemistry of both classes is linked due to their facile interconversion in the presence of acid or base catalysts. This interconversion, and the corresponding epimerization at sites alpha to the carbonyl functions, occurs by way of an enediol tautomeric intermediate. By clicking on the diagraman equation illustrating these isomerizations will be displayed. Because of base-catalyzed isomerizations of this kind, the Tollens’ reagent is not useful for distinguishing aldoses from ketoses or for specific nepali essay on my culture of aldoses to the corresponding aldonic acids. Oxidation by HOBr is preferred for the latter conversion. Fischer’s brilliant elucidation of the configuration of glucose did not remove all uncertainty concerning its structure. Two different crystalline forms of glucose were reported in 1895. Each of these gave all the characteristic reactions of glucose, and when dissolved in water equilibrated to the same mixture. This equilibration takes place over a period of many minutes, and the change in optical activity that occurs is called mutarotation. These facts are summarized in premium essay help diagram below. When glucose was converted to its pentamethyl ether (reaction with excess CH 3 I & AgOH), two different isomers were isolated, and neither exhibited the expected aldehyde reactions. Acid-catalyzed hydrolysis of the pentamethyl ether derivatives, however, gave a tetramethyl derivative that was oxidized by Tollen’s reagent and reduced by sodium borohydride, as expected for an aldehyde. These reactions will be displayed above by clicking on the diagram . The search for scientific truth often proceeds in stages, and the structural elucidation of glucose serves as a good example. It should be clear essay title generator the new evidence presented above, that the open chain pentahydroxyhexanal structure drawn essay title generator must be modified. Somehow a new stereogenic center must be created, and the aldehyde must be deactivated in the pentamethyl derivative. A simple solution to this dilemma is achieved by converting the open aldehyde structure for glucose into a cyclic hemiacetal, called a glucopyranoseas shown in the following diagram. The linear aldehyde is tipped on its side, and rotation about the C4-C5 bond brings the C5-hydroxyl function close to the aldehyde carbon. For ease of viewing, the six-membered hemiacetal structure is drawn as a flat hexagon, but it actually assumes a chair conformation. The hemiacetal carbon atom (C-1) becomes a new stereogenic center, commonly referred to as the anomeric carbonand the α and β-isomers are called anomers . We can now consider how this buy assignments of the glucose structure accounts for the puzzling facts noted above. First, we know that hemiacetals are in equilibrium with their carbonyl and alcohol components when in solution. Consequently, fresh solutions of either alpha or beta-glucose crystals in water should establish an equilibrium mixture of both anomers, plus the open chain chain form. This will be shown above by clicking on the diagram. Note that despite essay lengthener very low concentration of the open chain aldehyde in this mixture, typical chemical reactions of aldehydes take place rapidly. Second, a pentamethyl ether derivative of the pyranose structure converts the hemiacetal function to an acetal. Acetals are stable to base, so this product should not react with Tollen’s reagent or be reduced by sodium borohydride. Acid hydrolysis of acetals regenerates the carbonyl and alcohol components, and in the case of the glucose derivative this will be a tetramethyl ether of the pyranose hemiacetal. This compound will, of course, undergo typical aldehyde reactions. By clicking on the diagram a second time this relationship will be displayed above. As noted above, the essay writing service reddit structural form of many monosaccharides may be that of a cyclic hemiacetal. Five and six-membered rings are favored over other ring sizes because of their low angle and eclipsing strain. Cyclic structures of this kind are termed furanose (five-membered) or pyranose (six-membered), reflecting the help yourself essay size relationship to the common heterocyclic compounds furan and pyran shown on the right. Ribose, an important aldopentose, commonly adopts a furanose structure, as shown in the following illustration. By convention for the D-family, the five-membered furanose ring is an essay on the shaking palsy in an edgewise projection with the ring oxygen positioned away from the viewer. The anomeric carbon atom (colored red here) is placed on the right. The upper bond to this carbon is defined as beta, the lower bond then is alpha. Click on the following diagram to see a model of β-D-ribofuranose . The cyclic essay title generator forms of various monosaccharides are often drawn in a flat projection known as a Haworth formulaafter the British chemist, Norman Essay 24. As with the furanose ring, the anomeric carbon is placed on the right with the ring oxygen to the back of the edgewise view. In the D-family, the alpha and beta bonds have the same orientation defined for the furanose ring (beta is up & alpha is down). These Haworth formulas are convenient for displaying stereochemical relationships, but do not represent the true shape of the molecules. We know that these molecules are actually puckered in a fashion we call a chair conformation. Examples of four typical pyranose structures are shown below, both as Haworth projections and as the more representative chair conformers. The anomeric carbons are colored red. Models of these glucose, galactose, mannose and allose pyranose structures may be viewed by Clicking Here. A practice page for examining the configurations of aldohexoses may be viewed by Clicking Here. The size of the cyclic hemiacetal ring adopted by a given sugar is not constant, but may vary with substituents and learn write college assissgnmebnt structural features. Aldolhexoses usually form act essay help reddit rings and their pentose homologs tend to prefer the furanose form, but there are many counter examples. The formation of acetal derivatives illustrates how subtle changes may alter this selectivity. By clicking on the above diagram. the display will change to illustrate this. A pyranose structure for D-glucose is drawn in the rose-shaded box on the left. Acetal derivatives have been prepared by acid-catalyzed reactions with benzaldehyde and acetone. As a rule, benzaldehyde forms six-membered cyclic acetals, whereas acetone prefers to form five-membered acetals. The top equation shows the formation and some reactions of the 4,6-O-benzylidene acetal, a commonly employed protective group. A methyl glycoside derivative of this compound (see below) leaves the C-2 and C-3 hydroxyl groups exposed to reactions such as the periodic acid cleavage, shown as the last step. The formation of an isopropylidene acetal at C-1 and C-2, center structure, leaves the C-3 writing an essay on service as the only unprotected function. Selective oxidation to a ketone is then possible. Finally, direct di-O-isopropylidene derivatization of glucose by reaction with excess acetone results in a change to a furanose structure in which the C-3 hydroxyl is again unprotected. Informative essay 8th grade, the same reaction with D-galactose, shown in the blue-shaded box, produces a pyranose product in which the C-6 hydroxyl is unprotected. Both derivatives do not react with Tollens’ reagent. This difference in behavior is attributed to the cis-orientation of the C-3 and C-4 essay 2 paper groups in galactose, which permits formation of a less strained five-membered cyclic acetal, compared with the trans-C-3 and C-4 hydroxyl groups in glucose. Derivatizations essay about leadership this kind permit selective reactions to be conducted at different locations in these highly functionalized molecules. The ring size of these cyclic monosaccharides was determined by oxidation and chain cleavage of their tetra methyl ether derivatives. To see how this was done for glucose Click Here. Acetal derivatives formed when a monosaccharide reacts with an alcohol in the presence of an acid catalyst are called glycosides. This reaction is illustrated for glucose and methanol in the essay writing service review reddit below. In naming of glycosides, the “ose” suffix of the sugar name is replaced by “oside”, and the alcohol group name is placed first. As is generally true for most acetals, glycoside formation involves the loss of an equivalent of water. The diether product is stable to base and alkaline oxidants such as Tollen’s reagent. Since acid-catalyzed aldolization is reversible, glycosides may be hydrolyzed back to their alcohol and sugar components by aqueous acid. The anomeric methyl glucosides are formed in an equilibrium ratio of 66% alpha to 34% beta. From the structures in the previous diagram, we see that pyranose rings prefer chair conformations in which the largest number of substituents are equatorial. In the case of glucose, the substituents on the beta-anomer are all equatorial, whereas the C-1 substituent in the alpha-anomer changes to axial. Since substituents on cyclohexane rings prefer an equatorial location over axial (methoxycyclohexane is 75% equatorial), the preference for alpha-glycopyranoside formation is unexpected, and is referred to as the anomeric effect . Glycosides abound in biological systems. By attaching a sugar moiety to a lipid or benzenoid structure, the solubility and other properties of the compound may be changed substantially. Because of the important modifying influence of such derivatization, numerous enzyme systems, known as glycosidases, have evolved for the attachment and removal of sugars from alcohols, phenols and amines. Chemists refer to the sugar component of natural glycosides as the glycon chief essays the alcohol component as the aglycon. Two examples of naturally occurring glycosides and one example of an amino derivative will be displayed above by clicking on the diagram. Salicin, one of the oldest herbal remedies i dont wanna do my essay, was the model for the synthetic analgesic aspirin. A large class of hydroxylated, aromatic g p essays on education cations called anthocyanins provide the red, purple and an essay on new world order colors of many flowers, fruits and some vegetables. Peonin is one example of this class of natural pigments, which exhibit a pronounced pH what are some websites that give you an essay to write dependence. The oxonium moiety is only stable in acidic environments, and the color changes or disappears when base is added. The complex changes that occur when wine is fermented and stored are in part associated with glycosides of anthocyanins. Finally, amino derivatives of ribose, such as cytidine play important roles e-commerce essay topics biological phosphorylating agents, coenzymes and information transport and storage materials. For a discussion of the anomeric effect Click Here. For examples of structurally and functionally modified sugars Click Here. When the alcohol component of a glycoside is provided by a hydroxyl function on another monosaccharide, the compound is called a disaccharide. Four examples of disaccharides composed of two glucose units are shown in the following diagram. The individual glucopyranose rings are labeled A and B, and the glycoside bonding is circled in light blue. Notice that the glycoside bond may be alpha, essay questions for romeo and juliet in maltose and trehalose, or beta as in essay paper writer and gentiobiose. Acid-catalyzed hydrolysis of these disaccharides yields glucose as the only product. Enzyme-catalyzed hydrolysis is selective for a specific glycoside bond, so an alpha-glycosidase cleaves maltose and trehalose to glucose, but does not cleave cellobiose or gentiobiose. A beta-glycosidase has the opposite activity. In order custom essay.com draw a representative structure for cellobiose, one of the glucopyranose rings must be rotated by 180º, but this feature is often omitted in favor of retaining the usual perspective for the individual rings. The bonding between the glucopyranose rings in cellobiose and maltose is from the anomeric carbon in ring A to the C-4 hydroxyl group on ring B. This leaves the anomeric carbon in ring B free, so cellobiose and maltose both may assume alpha and beta anomers at that site (the beta form is shown in the diagram). Gentiobiose has a beta-glycoside link, originating at C-1 in ring A and terminating at C-6 in ring B. Its alpha-anomer is drawn in the diagram. Because cellobiose, maltose and gentiobiose are hemiacetals they are all reducing sugars (oxidized by Tollen’s reagent). Trehalose, a disaccharide found in certain mushrooms, is a bis-acetal, and is therefore a non-reducing sugar. A systematic nomenclature for disaccharides exists, but as the following examples illustrate, these are often lengthy. Cellobiose : 4-O-β-D-Glucopyranosyl-D-glucose (the beta-anomer is drawn) Maltose : 4-O-α-D-Glucopyranosyl-D-glucose (the beta-anomer is drawn) Gentiobiose : 6-O-β-D-Glucopyranosyl-D-glucose (the alpha-anomer is drawn) Trehalose : α-D-Glucopyranosyl-α-D-glucopyranoside. Although all the disaccharides shown here are made up of two glucopyranose rings, their properties differ in interesting ways. Maltose, sometimes called malt sugar, comes from the hydrolysis of starch. It is about one third as sweet as cane sugar (sucrose), is easily digested by humans, and is fermented by yeast. Cellobiose is obtained by the hydrolysis of cellulose. It has virtually buy an essay taste, is indigestible by humans, and is not fermented by yeast. Some bacteria have beta-glucosidase enzymes that hydrolyze the glycosidic bonds in cellobiose and cellulose. The presence of such bacteria in the digestive tracts of cows and termites permits essay examples pdf animals to use cellulose as a food. Finally, it may be noted that trehalose has a distinctly sweet taste, but gentiobiose is bitter. Disaccharides made up of other sugars are known, but glucose is often one of the components. Two important examples of such mixed disaccharides will be displayed above by clicking on the diagram. Lactose, also known as milk sugar, is a galactose-glucose compound joined as a beta-glycoside. It is a reducing sugar because of the hemiacetal function remaining in the glucose moiety. Many adults, particularly those from regions where milk is not a dietary staple, have a metabolic intolerance for lactose. Infants have a digestive enzyme which cleaves the beta-glycoside bond in lactose, but production of this enzyme stops with weaning. Cheese is less subject to the lactose intolerance problem, since most of the lactose is removed with the whey. Sucrose, or cane sugar, is our most commonly used sweetening agent. It is a non-reducing disaccharide composed of glucose and fructose joined at the anomeric carbon of each by glycoside bonds (one alpha and one beta). In the formula shown here the fructose ring has been rotated 180º from its conventional perspective. To essay topics for high school a model of sucrose Click Here. Additional Topics For a essay help discord discussion of sweetening agents Click Here. For examples of some larger saccharide oligomers Click Here. As the name implies, polysaccharides are large high-molecular weight molecules constructed by joining monosaccharide units together by glycosidic bonds. They are sometimes called glycans. The most important compounds in this class, cellulose, starch and glycogen are all polymers of glucose. This is easily demonstrated by acid-catalyzed hydrolysis to the monosaccharide. Since partial hydrolysis of cellulose gives varying amounts of cellobiose, we conclude the glucose essay title generator in this macromolecule are joined by beta-glycoside bonds between C-1 and C-4 sites of adjacent sugars. Partial hydrolysis of essay grading help and glycogen produces the disaccharide maltose together with low molecular weight dextrans, polysaccharides in which glucose molecules are joined by alpha-glycoside links between C-1 and C-6, as well as the alpha C-1 to C-4 essay title generator found in maltose. Polysaccharides built from other monosaccharides (e.g. mannose, galactose, xylose and arabinose) are also known, but will not be discussed here. Over half of the total organic carbon in the earth’s biosphere is in cellulose. Cotton fibers are essentially pure cellulose, and the wood of bushes and trees is about 50% cellulose. As a polymer of glucose, cellulose has the formula (C 6 H 10 O 5 ) n where n ranges from 500 to 5,000, depending on the source of the polymer. The glucose units in cellulose are linked in a linear fashion, as shown in the drawing below. The beta-glycoside bonds permit these chains to stretch out, and this conformation is stabilized by intramolecular hydrogen bonds. A parallel orientation of adjacent chains is also favored by intermolecular hydrogen bonds. Although an individual hydrogen bond is relatively weak, many such bonds acting together can impart great stability to certain conformations of large molecules. Most animals cannot digest cellulose as a food, and in the diets of humans this part of our vegetable intake functions as roughage and is eliminated buy capstone essay unchanged. Some animals (the cow and termites, for example) harbor intestinal microorganisms that breakdown cellulose into monosaccharide nutrients by the use of beta-glycosidase enzymes. Cellulose is commonly accompanied by a lower molecular weight, branched, amorphous essay writing service in london called hemicellulose. In contrast to cellulose, hemicellulose is structurally weak and is easily hydrolyzed by dilute acid or base. Also, many enzymes catalyze its hydrolysis. Hemicelluloses are composed of many D-pentose sugars, with xylose being the major component. Mannose and mannuronic acid are often present, as well as galactose and galacturonic acid. Starch is a polymer of glucose, found in roots, rhizomes, seeds, stems, essay title generator and corms of plants, as microscopic granules having characteristic shapes and sizes. Most animals, including humans, depend on these plant starches for nourishment. The structure of starch is more complex than that of cellulose. The intact granules are insoluble in cold water, but grinding or swelling them in warm water causes them to burst. The released starch consists of two fractions. About 20% is a water soluble material called amylose. Molecules of amylose are linear chains of several thousand glucose units joined by alpha C-1 to C-4 glycoside bonds. Amylose solutions are actually dispersions of hydrated helical micelles. The majority of the starch is a much higher molecular weight substance, consisting of nearly a million glucose units, and called amylopectin. Molecules of amylopectin are branched networks built from C-1 to C-4 and Essay help us to C-6 glycoside links, and are essentially water insoluble. Representative structural formulas for amylose and amylopectin will be shown above by clicking on the diagram. To see an expanded structure for essay v for vendetta click again on the diagram. The branching in this diagram is exaggerated, since on average, branches only occur every twenty five glucose units. Hydrolysis of starch, usually by enzymatic reactions, produces a syrupy liquid consisting largely of glucose. When cornstarch is the feedstock, this product is known as corn syrup. It is widely used to soften texture, add volume, prohibit crystallization and enhance the flavor of foods. Glycogen is the glucose storage polymer used by animals. It has a structure similar to amylopectin, but is even more highly branched (about every tenth glucose unit). The degree of branching in these polysaccharides may be measured by enzymatic or chemical analysis. For examples of chemical analysis of branching Click Here. Cotton, probably the most useful natural fiber, is nearly pure cellulose. The manufacture of textiles from cotton involves physical manipulation of the raw material by carding, combing and spinning selected fibers. For fabrics the best cotton has long fibers, and short fibers or cotton dust are removed. Crude cellulose is also available from wood pulp by cheap essay papers online the lignan matrix surrounding it. These less desirable cellulose sources are widely used for making paper. In order to expand the ways in which cellulose can be put to practical use, chemists have devised techniques for preparing solutions of cellulose derivatives that can be spun into fibers, spread into a film or cast in various solid forms. A key factor in these transformations are the three free hydroxyl groups on each glucose unit in the cellulose chain, –[C 6 H 7 O(OH) 3 ] n –. Esterification of these functions leads to essay reader products having very different properties compared with cellulose itself. Cellulose Nitratefirst prepared over 150 years ago by treating cellulose with nitric acid, is the earliest synthetic polymer to see general use. The fully nitrated compound, –[C 6 H 7 O(ONO 2 ) 3 ] n –, called guncotton, is explosively flammable and is a component of smokeless powder. Partially nitrated cellulose is called pyroxylin. Pyroxylin is soluble in ether and at one time was used for photographic film and lacquers. The high flammability of pyroxylin caused many tragic cinema fires during its period of use. Furthermore, slow hydrolysis of pyroxylin yields nitric acid, a process that contributes to the deterioration of early motion picture films in storage. Cellulose Acetate–[C 6 H 7 O(OAc) 3 ] n –, is less flammable than pyroxylin, and has replaced it in most applications. It is prepared by reaction of cellulose with acetic anhydride paper review service an acid catalyst. The properties of the product vary with the degree of acetylation. Some chain shortening occurs unavoidably in the preparations. An acetone solution of cellulose acetate may be forced through a spinneret to generate filaments, called acetate rayonthat can be woven into fabrics. Viscose Rayonis prepared by formation of an alkali soluble xanthate derivative that can be spun into a fiber that reforms the cellulose polymer by acid quenching. The following general equation illustrates these transformations. The product fiber is called viscose rayon .