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Macromolecules and Behavior | BioScience | Oxford Academic
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UCST and LCST Behavior in Polymer Blends and Its Thermodynamic Interpretation
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Cells are surrounded by a membrane, which has a bilayer of phospholipids. The fatty acids of phospholipids face inside, away from water, whereas the phosphate group can face either the outside environment or the inside of the cell, which are both aqueous. Unlike the phospholipids and fats discussed earlier, steroids have a ring structure. Although they do not resemble other lipids, they are grouped with them because they are also hydrophobic.
All steroids have four, linked carbon rings and several of them, like cholesterol, have a short tail. Cholesterol is a steroid. Cholesterol is mainly synthesized in the liver and is the precursor of many steroid hormones, such as testosterone and estradiol. It is also the precursor of vitamins E and K. Cholesterol is the precursor of bile salts, which help in the breakdown of fats and their subsequent absorption by cells.
Although cholesterol is often spoken of in negative terms, it is necessary for the proper functioning of the body. It is a key component of the plasma membranes of animal cells. Waxes are made up of a hydrocarbon chain with an alcohol —OH group and a fatty acid. Examples of animal waxes include beeswax and lanolin. Plants also have waxes, such as the coating on their leaves, that helps prevent them from drying out. Proteins are one of the most abundant organic molecules in living systems and have the most diverse range of functions of all macromolecules.
Proteins may be structural, regulatory, contractile, or protective; they may serve in transport, storage, or membranes; or they may be toxins or enzymes. Each cell in a living system may contain thousands of different proteins, each with a unique function. Their structures, like their functions, vary greatly.
They are all, however, polymers of amino acids, arranged in a linear sequence. The functions of proteins are very diverse because there are 20 different chemically distinct amino acids that form long chains, and the amino acids can be in any order. For example, proteins can function as enzymes or hormones. Enzymes , which are produced by living cells, are catalysts in biochemical reactions like digestion and are usually proteins. Each enzyme is specific for the substrate a reactant that binds to an enzyme upon which it acts.
Enzymes can function to break molecular bonds, to rearrange bonds, or to form new bonds. An example of an enzyme is salivary amylase, which breaks down amylose, a component of starch. Hormones are chemical signaling molecules, usually proteins or steroids, secreted by an endocrine gland or group of endocrine cells that act to control or regulate specific physiological processes, including growth, development, metabolism, and reproduction.
For example, insulin is a protein hormone that maintains blood glucose levels. Proteins have different shapes and molecular weights; some proteins are globular in shape whereas others are fibrous in nature. For example, hemoglobin is a globular protein, but collagen, found in our skin, is a fibrous protein. Protein shape is critical to its function. Changes in temperature, pH, and exposure to chemicals may lead to permanent changes in the shape of the protein, leading to a loss of function or denaturation to be discussed in more detail later.
All proteins are made up of different arrangements of the same 20 kinds of amino acids. Amino acids are the monomers that make up proteins. Each amino acid has the same fundamental structure, which consists of a central carbon atom bonded to an amino group —NH 2 , a carboxyl group —COOH , and a hydrogen atom. Every amino acid also has another variable atom or group of atoms bonded to the central carbon atom known as the R group. The R group is the only difference in structure between the 20 amino acids; otherwise, the amino acids are identical.
The chemical nature of the R group determines the chemical nature of the amino acid within its protein that is, whether it is acidic, basic, polar, or nonpolar. Each amino acid is attached to another amino acid by a covalent bond, known as a peptide bond, which is formed by a dehydration reaction.
The carboxyl group of one amino acid and the amino group of a second amino acid combine, releasing a water molecule. The resulting bond is the peptide bond. The products formed by such a linkage are called polypeptides. While the terms polypeptide and protein are sometimes used interchangeably, a polypeptide is technically a polymer of amino acids, whereas the term protein is used for a polypeptide or polypeptides that have combined together, have a distinct shape, and have a unique function.
The Evolutionary Significance of Cytochrome cCytochrome c is an important component of the molecular machinery that harvests energy from glucose. For example, scientists have determined that human cytochrome c contains amino acids. For each cytochrome c molecule that has been sequenced to date from different organisms, 37 of these amino acids appear in the same position in each cytochrome c.
This indicates that all of these organisms are descended from a common ancestor. On comparing the human and chimpanzee protein sequences, no sequence difference was found. When human and rhesus monkey sequences were compared, a single difference was found in one amino acid. In contrast, human-to-yeast comparisons show a difference in 44 amino acids, suggesting that humans and chimpanzees have a more recent common ancestor than humans and the rhesus monkey, or humans and yeast. As discussed earlier, the shape of a protein is critical to its function.
To understand how the protein gets its final shape or conformation, we need to understand the four levels of protein structure: primary, secondary, tertiary, and quaternary. The unique sequence and number of amino acids in a polypeptide chain is its primary structure. The unique sequence for every protein is ultimately determined by the gene that encodes the protein. Any change in the gene sequence may lead to a different amino acid being added to the polypeptide chain, causing a change in protein structure and function. What is most remarkable to consider is that a hemoglobin molecule is made up of two alpha chains and two beta chains that each consist of about amino acids.
The molecule, therefore, has about amino acids. The structural difference between a normal hemoglobin molecule and a sickle cell molecule—that dramatically decreases life expectancy in the affected individuals—is a single amino acid of the This can lead to a myriad of serious health problems, such as breathlessness, dizziness, headaches, and abdominal pain for those who have this disease. Folding patterns resulting from interactions between the non-R group portions of amino acids give rise to the secondary structure of the protein.
Both structures are held in shape by hydrogen bonds. In the alpha helix, the bonds form between every fourth amino acid and cause a twist in the amino acid chain. The R groups are attached to the carbons, and extend above and below the folds of the pleat. The pleated segments align parallel to each other, and hydrogen bonds form between the same pairs of atoms on each of the aligned amino acids. The unique three-dimensional structure of a polypeptide is known as its tertiary structure. This structure is caused by chemical interactions between various amino acids and regions of the polypeptide.
Primarily, the interactions among R groups create the complex three-dimensional tertiary structure of a protein. There may be ionic bonds formed between R groups on different amino acids, or hydrogen bonding beyond that involved in the secondary structure.
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For example, hemoglobin is a combination of four polypeptide subunits. Each protein has its own unique sequence and shape held together by chemical interactions. If the protein is subject to changes in temperature, pH, or exposure to chemicals, the protein structure may change, losing its shape in what is known as denaturation as discussed earlier. Denaturation is often reversible because the primary structure is preserved if the denaturing agent is removed, allowing the protein to resume its function.
Sometimes denaturation is irreversible, leading to a loss of function. One example of protein denaturation can be seen when an egg is fried or boiled. The albumin protein in the liquid egg white is denatured when placed in a hot pan, changing from a clear substance to an opaque white substance. Not all proteins are denatured at high temperatures; for instance, bacteria that survive in hot springs have proteins that are adapted to function at those temperatures.
Nucleic acids are key macromolecules in the continuity of life. They carry the genetic blueprint of a cell and carry instructions for the functioning of the cell. DNA is the genetic material found in all living organisms, ranging from single-celled bacteria to multicellular mammals. The other type of nucleic acid, RNA, is mostly involved in protein synthesis.
The DNA molecules never leave the nucleus, but instead use an RNA intermediary to communicate with the rest of the cell. Other types of RNA are also involved in protein synthesis and its regulation. Each nucleotide is made up of three components: a nitrogenous base, a pentose five-carbon sugar, and a phosphate group.
Each nitrogenous base in a nucleotide is attached to a sugar molecule, which is attached to a phosphate group. It is composed of two strands, or polymers, of nucleotides. The strands are formed with bonds between phosphate and sugar groups of adjacent nucleotides. The alternating sugar and phosphate groups lie on the outside of each strand, forming the backbone of the DNA. The nitrogenous bases are stacked in the interior, like the steps of a staircase, and these bases pair; the pairs are bound to each other by hydrogen bonds.
The bases pair in such a way that the distance between the backbones of the two strands is the same all along the molecule. The rule is that nucleotide A pairs with nucleotide T, and G with C, see section 9. Living things are carbon-based because carbon plays such a prominent role in the chemistry of living things. The four covalent bonding positions of the carbon atom can give rise to a wide diversity of compounds with many functions, accounting for the importance of carbon in living things.
Carbohydrates are a group of macromolecules that are a vital energy source for the cell, provide structural support to many organisms, and can be found on the surface of the cell as receptors or for cell recognition. Carbohydrates are classified as monosaccharides, disaccharides, and polysaccharides, depending on the number of monomers in the molecule.
Lipids are a class of macromolecules that are nonpolar and hydrophobic in nature. Major types include fats and oils, waxes, phospholipids, and steroids. Fats and oils are a stored form of energy and can include triglycerides. Fats and oils are usually made up of fatty acids and glycerol. Proteins are a class of macromolecules that can perform a diverse range of functions for the cell. They help in metabolism by providing structural support and by acting as enzymes, carriers or as hormones.
The building blocks of proteins are amino acids.
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Proteins are organized at four levels: primary, secondary, tertiary, and quaternary. Protein shape and function are intricately linked; any change in shape caused by changes in temperature, pH, or chemical exposure may lead to protein denaturation and a loss of function. Nucleic acids are molecules made up of repeating units of nucleotides that direct cellular activities such as cell division and protein synthesis.
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Each nucleotide is made up of a pentose sugar, a nitrogenous base, and a phosphate group. Explain what happens if even one amino acid is substituted for another in a polypeptide chain. Provide a specific example. Ophardt, C. In Biological Chemistry. Gunawardena, G.
Snell, Foster D. Use Your Creativity to Make a Difference! Review Questions: 1. What are the monomers that make up proteins called? Where is the linkage made that combines two amino acids?
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The alpha-helix and the beta-pleated sheet are part of which protein structure? Which of the following may cause a protein to denature? 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. Triglycerides comprise three fatty acids bonded to glycerol, yielding a hydrophobic molecule.
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.
A wax is a long-chain isoprenoid that is typically water resistant; an example of a wax-containing substance is sebum, produced by sebaceous glands in the skin. Bacteria produce hopanoids, structurally similar to cholesterol, to strengthen bacterial membranes. Fungi and protozoa produce a strengthening agent called ergosterol. Multiple Choice Which of the following describes lipids?
Critical Thinking Microorganisms can thrive under many different conditions, including high-temperature environments such as hot springs. Short Answer Describe the structure of a typical phospholipid. Introduction Glyceraldehyde can exist in two isomeric forms that are mirror images of each other which are shown below. Introduction The chemistry of carbohydrates most closely resembles that of alcohol, aldehyde, and ketone functional groups.
Di- and Poly-Carbohydrates Monosaccharides contain one sugar unit such as glucose , galactose , fructose , etc. Disaccharides contain two sugar units. In almost all cases one of the sugars is glucose, with the other sugar being galactose, fructose, or another glucose. Common disaccharides are maltose, lactose , and sucrose. Polysaccharides contain many sugar units in long polymer chains of many repeating units. The most common sugar unit is glucose. Common poly saccharides are starch , glycogen , and cellulose.
Common Polysaccharides Starch Plants store glucose as the polysaccharide starch. The cereal grains wheat, rice, corn, oats, barley as well as tubers such as potatoes are rich in starch. Cellulose The major component in the rigid cell walls in plants is cellulose and is a linear polysaccharide polymer with many glucose monosaccharide units. Glycogen This is the storage form of glucose in animals and humans which is analogous to the starch in plants.
Glycogen is synthesized and stored mainly in the liver and the muscles. Metabolism Metabolism occurs in animals and humans after the ingestion of organic plant or animal foods. This representation of rings is known as the Haworth formula. Step 1 : Draw the Fischer projection of the acyclic form of D-glucose. See D,L convention Step 2 : Number the carbon chain in 1 starting at the top.
Step 3 : To generate the pyranose ring, the oxygen atom on C-5 in 1 needs to be attached to C-1 by a single bond. In 1, C-1 is behind the plane of the paper and the hydroxy group on C-5 is in front. For the pyranose ring to be planar, both C-1 and the hydroxy group on C-5 have to be either behind or in front of the plane of the paper. C-5 is a chiral center. Step 5 : Redraw the atom chain along the horizontal axis as follows. Step 8 : Add the two remaining bonds to C-1 in 6. The hydrocarbon chain length may vary from carbons most usual is The non-polar hydrocarbon alkane chain is an important counter balance to the polar acid functional group.
In acids with only a few carbons, the acid functional group dominates and gives the whole molecule a polar character. However, in fatty acids, the non-polar hydrocarbon chain gives the molecule a non-polar character. Fatty acids are merely carboxylic acids with long hydrocarbon chains. Introduction The most common fatty acids are listed. Melting Points of Saturated vs. Unsaturated Fatty Acids Note that as a group, the unsaturated fatty acids have lower melting points than the saturated fatty acids. Hydrogenation Reaction Unsaturated fatty acids may be converted to saturated fatty acids by the relatively simple hydrogenation reaction.
Figure 1: Hydrogenation of a oleic fatty acid Vegetable oils which have been partially hydrogenated, are now partially saturated so the melting point increases to the point where a solid is present at room temperature. Trans Fat A major health concern during the hydrogenation process is the production of trans fats. Prostaglandins were first discovered and isolated from human semen in the s by Ulf von Euler of Sweden. Thinking they had come from the prostate gland, he named them prostaglandins.
It has since been determined that they exist and are synthesized in virtually every cell of the body. Prostaglandins, are like hormones in that they act as chemical messengers, but do not move to other sites, but work right within the cells where they are synthesized. Introduction Prostaglandins are unsaturated carboxylic acids, consisting of of a 20 carbon skeleton that also contains a five member ring. Prostaglandin Structure Prostaglandins are unsaturated carboxylic acids, consisting of of a 20 carbon skeleton that also contains a five member ring and are based upon the fatty acid, arachidonic acid.
Functions of Prostaglandins There are a variety of physiological effects including: Activation of the inflammatory response, production of pain, and fever. When tissues are damaged, white blood cells flood to the site to try to minimize tissue destruction. Prostaglandins are produced as a result.
Blood clots form when a blood vessel is damaged. A type of prostaglandin called thromboxane stimulates constriction and clotting of platelets. Conversely, PGI2, is produced to have the opposite effect on the walls of blood vessels where clots should not be forming. Certain prostaglandins are involved with the induction of labor and other reproductive processes. PGE2 causes uterine contractions and has been used to induce labor.
Prostaglandins are involved in several other organs such as the gastrointestinal tract inhibit acid synthesis and increase secretion of protective mucus , increase blood flow in kidneys, and leukotriens promote constriction of bronchi associated with asthma. Effects of Aspirin and other Pain Killers When you see that prostaglandins induce inflammation, pain, and fever, what comes to mind but aspirin. Glycerides and waxes are lipids with have an ester as the major functional group and include: waxes, triglycerides, and phospholipids. Triglycerides are esters of fatty acids and a trifunctional alcohol — glycerol IUPAC name is 1,2,3-propantriol.
The properties of fats and oils follow the same general principles as already described for the fatty acids. The important properties to be considered are: melting points and degree of unsaturation from component fatty acids. Introduction Since glycerol has three alcohol functional groups, three fatty acids must react to make three ester functional groups.
The common fats and oils including fatty acid content are listed below. Synthesis of a Triglyceride Since glycerol, IUPAC name is 1,2,3-propantriol , has three alcohol functional groups, three fatty acids must react to make three ester functional groups. Structure of a Triglyceride As you can see from the graphic on the left, the actual molecular model of the triglyceride does not look at all like the line drawing.
Introduction The third oxygen on glycerol is bonded to phosphoric acid through a phosphate ester bond oxygen-phosphorus double bond oxygen. There are two common phospholipids: Lecithin contains the amino alcohol, choline. Cephalins contain the amino alcohols serine or ethanolamine. Lecithin Lecithin is probably the most common phospholipid. Cephalins Cephalins are phosphoglycerides that contain ehtanolamine or the amino acid serine attached to the phosphate group through phosphate ester bonds.
One major class of lipids is the steroids, which have structures totally different from the other classes of lipids. The main feature of steroids is the ring system of three cyclohexanes and one cyclopentane in a fused ring system as shown below. There are a variety of functional groups that may be attached. The main feature, as in all lipids, is the large number of carbon-hydrogens which make steroids non-polar. Introduction Steroids include such well known compounds as cholesterol, sex hormones, birth control pills, cortisone, and anabolic steroids. Cholesterol The best known and most abundant steroid in the body is cholesterol.
Structures of Sex Hormones Sex hormones are also steroids. Learning Objectives By the end of this section, you will be able to: Describe the ways in which carbon is critical to life Explain the impact of slight changes in amino acids on organisms Describe the four major types of biological molecules Understand the functions of the four major types of molecules. Evolution in Action The Evolutionary Significance of Cytochrome cCytochrome c is an important component of the molecular machinery that harvests energy from glucose.
It can also provide insulation. Phospholipids and steroids are important components of cell membranes. A change in gene sequence can lead to a different amino acid being added to a polypeptide chain instead of the normal one. This causes a change in protein structure and function. Because of this change, the disc-shaped red blood cells assume a crescent shape, which can result in serious health problems. OpenStax , Proteins. OpenStax CNX. OpenStax, Microbiology. Apply Get info Visit us. Disaccharides — contain two monosaccharides. Common Polysaccharides. Plants store glucose as the polysaccharide starch.
The major component in the rigid cell walls in plants is cellulose and is a linear polysaccharide polymer with many glucose monosaccharide units. This is the storage form of glucose in animals and humans which is analogous to the starch in plants. Quiz: Which acid short chain or fatty would most likely be soluble in water? What is the molecular geometry of all three carbons in glycerol look at model above? What is the molecular geometry of the carbon at the center of the ester group?
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