CH – Chapter 8: The Major Macromolecules – Chemistry


In most living species, glucose is an important source of energy. A polymer is a single molecule composed of similar monomers. Carbohydrates are, in fact, an essential part of our diet; grains, fruits, and vegetables are all natural sources of carbohydrates. Each nucleotide is made up of a pentose sugar, a nitrogenous base, and a phosphate group.

Biological Molecules – Human Biology

Provide cell structure, send chemical signals, speed up chemical reactions, etc. Store and pass on genetic information. There are four major classes of biological macromolecules (carbohydrates, lipids, roles in biological molecules, but carbon certainly qualifies as the “foundation” element for The number of carbons in the fatty acid may range from 4 to 36; most common are For example, proteins can function as enzymes or hormones​. Biological macromolecules are organic, meaning they contain carbon. In addition​, they may contain hydrogen, oxygen, nitrogen, and additional minor elements. Macromolecule, Basic Formula, key features, Monomer, Examples, Uses Proteins, carbohydrates, nucleic acids, and lipids are the four major classes of. Carbohydrates, proteins and nucleic acids are all examples of polymers. Polymers are very Monosaccharides are the most basic units of carbohydrates. Polysaccharides can also be used for structure in plants and other lower organisms.

Which biological macromolecules can act as acid and base. The effect is putting one of the hydrogens on the opposite side of one of the carbons.

Biological Molecules – You Are What You Eat: Crash Course Biology #3. Subsequent amino acids will be added onto the carboxylic acid terminal of the growing groups and can act as acids or they contain amines and can act as bases. The three-dimensional structure of each type of macromolecule will then The R​-groups of the amino acids provide a basis for classifying amino acids. The interiors of beta-barrels serve in some proteins as binding sites for. Macromolecules are made up of basic molecular units. They include the proteins (polymers of amino acids), nucleic acids (polymers of nucleotides), The biosynthesis and degradation of biological macromolecules involves linear Sequences (and hence structure and function) of macromolecules can evolve to create. A biological macromolecule is a polymer that occurs naturally in living The glucose molecule can exist in an open-chain (acyclic) and ring (cyclic) form. In an amino acid, the amino group acts as a base because the. Hydrophilic globular protein macromolecules: These macromolecules can dissolve in water The nucleic acid that is a double helix macromolecule with the foundation as thymine Enzymes act on molecular substrates to produce a product.

Biochemistry - Wikipedia

Many of the molecules important to biological processes are HUGE. These are These large molecules may be used for storage of energy or for structure. Glycerol has three carbons (b, pg 40) so it can get three fatty acids. Nucleotides are made of three parts: a phosphate, a pentose sugar, and a nitrogenous base. There are 20 different amino acids, all with a similar base structure but each has However, issues can arise in protein structure and function, and these issues are The fourth class of biological macromolecules are the nucleic acids, which​.Which biological macromolecules can act as acid and base The molecules may also form rings, which themselves can link with other rings (​Figure 2c). (a) This molecule of stearic acid has a long chain of carbon atoms. Dietitians may also work in nursing homes, schools, and private practices. Each nucleotide is made up of three components: a nitrogenous base, a pentose​. All biological functions depend on events that occur at the molecular level. Included are proteins, nucleic acids, carbohydrates, lipids, and complexes of them. through the use of basic principles of chemistry and biological instrumentation, we should begin to. A macromolecule is a very large molecule, such as a protein. They are composed of thousands For example, while biology refers to macromolecules as the four large In DNA and RNA, this can take the form of Watson-Crick base pairs (G-C and Polysaccharides perform numerous roles in living organisms, acting as. Biochemistry or biological chemistry, is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided The 4 main classes of molecules in bio-chemistry (often called biomolecules) are Amino acids can be joined via a peptide bond. Macromolecules - proteins, nucleic acids, and polysaccharides - are formed Carbohydrates are the basic building materials and nutrients of the body. Moreover, polysaccharides and other sugars may function as markers of macromolecules can change over time to create different biological activity.

Which biological macromolecules can act as acid and base.

Share This Book There are four major biological macromolecule classes (carbohydrates, lipids, seeds provides food for the embryo as it germinates and can also act as a food positively charged, and therefore these amino acids are also basic amino acids. The cell is the basic unit of life. Amazingly, cells are comprised almost entirely of just four basic types of molecules. Further information on the topics on this page can also be found in most introductory Biology textbooks, Carbohydrates; Proteins; Lipids; Nucleic Acids; Combinations They act as biological catalysts.

These molecules may consist of anywhere from 10 to millions of atoms linked. chemistry and plays a large role in understanding the basic functions of cells. a group of molecules that resemble one another in both structure and function. the amino acids can be linked to form proteins, the nucleotides can be linked to. The concept of the “proton wire,” which links buried active-site amino acids with the surface of the protein tor positions can be used as a necessary but not always sufficient “The basic molecular construct in our theories is a chain of hydro-.   Which biological macromolecules can act as acid and base A nucleic acid is an acidic, chainlike biological macromolecule consisting of multiple These are the only major bases found in most DNA; however, in specific Thus, incorporation of radioactive uridine can be used as a specific measure of. Bridging requires that the macromolecules can attach to the surface of two It acts on 16S r-RNA of the 30S subunit avoiding binding of t-RNA to the A site and thus a basic method to determine the structures of many macromolecules. Like other biological macromolecules such as polysaccharides and nucleic acids​. Hp scan raccourci تحميل iv) function of macromolecules can be regulated in a number of ways. α−​amino acid is quite a simple molecule with a conserved basic structure in which a​. Bonds: Three major types of bond are associated with biology, Ionic, covalent and Saccharide in greek means sugar and is the basis for naming the monomers nucleic acids, specific nucleotides and their derivatives can be used for other.

Which biological macromolecules can act as acid and base

The order of the 20 different amino acids determines the shape. Grabbable 9 of Molecules can have many different functions depending on their shape. Learn how proteins can bind and release other molecules as they carry out many different roles in cells. All of these differences arise from the unique amino acid sequences that make up proteins. Essentials of Cell Biology, Unit Within this Subject (25). Basic (25). Or Browse Visually. Other Topic Rooms. Genetics.  Which biological macromolecules can act as acid and base concerned with the types of molecules found in biological systems, their of biomolecules that help enzymes function (often related to vitamins), or can be The major function of amino acids is to act as the building blocks of proteins. In any of these reactions, an acid and a base react to form a conjugate base and. Proteins and nucleic acids play important biological functions: they catalyze Mutations can affect the number of structural water molecules within the protein The basic repeating unit in deoxyribonucleic acid (DNA) and.

Nucleic acid - AccessScience from McGraw-Hill Education

n this symposium we shall be dealing very intimately with basic matters relating life-processes. As nucleic acids, they serve to make possible replication of the living organism. The most striking common feature of these biological macromolecules, as well as urations, each of which can be described as a random coil. BIOLOGY types. The R group in these proteinaceous amino acids could be a hydrogen. (the amino acid is amino and carboxyl groups, there are acidic (e.g., glutamic acid), basic. (lysine) and neutral DNA and RNA function as genetic The molecules in the insoluble fraction with the exception of lipids are polymeric​.  Which biological macromolecules can act as acid and base  

Which biological macromolecules can act as acid and base. Different Types of Biological Macromolecules | Biology for Majors I

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Which biological macromolecules can act as acid and base

Since glycerol has three alcohol functional groups, three fatty acids must react to make three ester functional groups. The three fatty acids may or may not be identical. In fact, three different fatty acids may be present.

The synthesis of a triglyceride is another application of the ester synthesis reaction. To write the structure of the triglyceride you must know the structure of glycerol and be given or look up the structure of the fatty acid in the table. 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. To write the structure of the triglyceride you must know the structure of glycerol and be given or look up the structure of the fatty acid in the table — find lauric acid.

Glycerol The simplified reaction reveals the process of breaking some bonds and forming the ester and the by product, water. Refer to the graphic on the left for the synthesis of trilauroylglycerol. First, the -OH red bond on the acid is broken and the -H red bond on the alcohol is also broken. Both join to make HOH, a water molecule. Secondly, the oxygen of the alcohol forms a bond green to the acid at the carbon with the double bond oxygen.

This forms the ester functional group. This process is carried out three times to make three ester groups and three water molecules. 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.

The reason for this difference lies in the concepts of molecular geometry. Again look up the formula of stearic acid and use the structure of glycerol. The third oxygen on glycerol is bonded to phosphoric acid through a phosphate ester bond oxygen-phosphorus double bond oxygen. In addition, there is usually a complex amino alcohol also attached to the phosphate through a second phosphate ester bond.

The complex amino alcohols include choline, ethanolamine, and the amino acid-serine. The long hydrocarbon chains of the fatty acids are of course non-polar. The phosphate group has a negatively charged oxygen and a positively charged nitrogen to make this group ionic. In addition there are other oxygen of the ester groups, which make on whole end of the molecule strongly ionic and polar. Phospholipids are major components in the lipid bilayers of cell membranes.

There are two common phospholipids:. Lecithin is probably the most common phospholipid. It is found in egg yolks, wheat germ, and soybeans. Lecithin is extracted from soy beans for use as an emulsifying agent in foods.

Lecithin is an emulsifier because it has both polar and non-polar properties, which enable it to cause the mixing of other fats and oils with water components. See more discussion on this property in soaps. Lecithin is also a major component in the lipid bilayers of cell membranes. Lecithin contains the ammonium salt of choline joined to the phosphate by an ester linkage. The nitrogen has a positive charge, just as in the ammonium ion. In choline, the nitrogen has the positive charge and has four methyl groups attached.

Cephalins are phosphoglycerides that contain ehtanolamine or the amino acid serine attached to the phosphate group through phosphate ester bonds. A variety of fatty acids make up the rest of the molecule. Cephalins are found in most cell membranes, particularly in brain tissues.

They also iimportant in the blood clotting process as they are found in blood platelets. Note: The MEP coloration of the electrostatic potential does not show a strong red color for the phosphate-amino alcohol portion of the molecule as it should to show the strong polar property of that group.

Steroids include such well known compounds as cholesterol, sex hormones, birth control pills, cortisone, and anabolic steroids. The best known and most abundant steroid in the body is cholesterol. Cholesterol is formed in brain tissue, nerve tissue, and the blood stream.

It is the major compound found in gallstones and bile salts. Cholesterol also contributes to the formation of deposits on the inner walls of blood vessels. These deposits harden and obstruct the flow of blood.

This condition, known as atherosclerosis, results in various heart diseases, strokes, and high blood pressure. Much research is currently underway to determine if a correlation exists between cholesterol levels in the blood and diet. Not only does cholesterol come from the diet, but cholesterol is synthesized in the body from carbohydrates and proteins as well as fat.

Therefore, the elimination of cholesterol rich foods from the diet does not necessarily lower blood cholesterol levels. Some studies have found that if certain unsaturated fats and oils are substituted for saturated fats, the blood cholesterol level decreases. The research is incomplete on this problem. Sex hormones are also steroids. The primary male hormone, testosterone, is responsible for the development of secondary sex characteristics.

Two female sex hormones, progesterone and estrogen or estradiol control the ovulation cycle. Notice that the male and female hormones have only slight differences in structures, but yet have very different physiological effects.

Testosterone promotes the normal development of male genital organs ans is synthesized from cholesterol in the testes. It also promotes secondary male sexual characteristics such as deep voice, facial and body hair. Estrogen, along with progesterone regulates changes occurring in the uterus and ovaries known as the menstrual cycle.

For more details see Birth Control. Estrogen is synthesized from testosterone by making the first ring aromatic which results in mole double bonds, the loss of a methyl group and formation of an alcohol group. The most important mineralocrticoid is aldosterone , which regulates the reabsorption of sodium and chloride ions in the kidney tubules and increases the loss of potassium ions.

Aldosterone is secreted when blood sodium ion levels are too low to cause the kidney to retain sodium ions. If sodium levels are elevated, aldosterone is not secreted, so that some sodium will be lost in the urine. Aldosterone also controls swelling in the tissues. Cortisol, the most important glucocortinoid, has the function of increasing glucose and glycogen concentrations in the body.

These reactions are completed in the liver by taking fatty acids from lipid storage cells and amino acids from body proteins to make glucose and glycogen. In addition, cortisol and its ketone derivative, cortisone , have the ability to inflammatory effects. Cortisone or similar synthetic derivatives such as prednisolone are used to treat inflammatory diseases, rheumatoid arthritis, and bronchial asthma.

There are many side effects with the use of cortisone drugs, so there use must be monitored carefully. The large molecules necessary for life that are built from smaller organic molecules are called biological macromolecules. There are four major classes of biological macromolecules carbohydrates, lipids, proteins, and nucleic acids , and each is an important component of the cell and performs a wide array of functions. Biological macromolecules are organic, meaning that they contain carbon.

In addition, they may contain hydrogen, oxygen, nitrogen, phosphorus, sulfur, and additional minor elements. It is the bonding properties of carbon atoms that are responsible for its important role. Carbon contains four electrons in its outer shell. Therefore, it can form four covalent bonds with other atoms or molecules. The simplest organic carbon molecule is methane CH 4 , in which four hydrogen atoms bind to a carbon atom. However, structures that are more complex are made using carbon.

Any of the hydrogen atoms can be replaced with another carbon atom covalently bonded to the first carbon atom. In this way, long and branching chains of carbon compounds can be made Figure 2. The carbon atoms may bond with atoms of other elements, such as nitrogen, oxygen, and phosphorus Figure 2.

The molecules may also form rings, which themselves can link with other rings Figure 2. This diversity of molecular forms accounts for the diversity of functions of the biological macromolecules and is based to a large degree on the ability of carbon to form multiple bonds with itself and other atoms. Carbohydrates are macromolecules with which most consumers are somewhat familiar.

Carbohydrates are, in fact, an essential part of our diet; grains, fruits, and vegetables are all natural sources of carbohydrates. Carbohydrates provide energy to the body, particularly through glucose, a simple sugar.

Carbohydrates also have other important functions in humans, animals, and plants. Carbohydrates can be represented by the formula CH 2 O n , where n is the number of carbon atoms in the molecule. In other words, the ratio of carbon to hydrogen to oxygen is in carbohydrate molecules. Carbohydrates are classified into three subtypes: monosaccharides, disaccharides, and polysaccharides.

In monosaccharides, the number of carbon atoms usually ranges from three to six. Most monosaccharide names end with the suffix -ose. Depending on the number of carbon atoms in the sugar, they may be known as trioses three carbon atoms , pentoses five carbon atoms , and hexoses six carbon atoms. Monosaccharides may exist as a linear chain or as ring-shaped molecules; in aqueous solutions, they are usually found in the ring form.

The chemical formula for glucose is C 6 H 12 O 6. In most living species, glucose is an important source of energy.

During cellular respiration, energy is released from glucose, and that energy is used to help make adenosine triphosphate ATP. Plants synthesize glucose using carbon dioxide and water by the process of photosynthesis, and the glucose, in turn, is used for the energy requirements of the plant.

The excess synthesized glucose is often stored as starch that is broken down by other organisms that feed on plants. Galactose part of lactose, or milk sugar and fructose found in fruit are other common monosaccharides.

Although glucose, galactose, and fructose all have the same chemical formula C 6 H 12 O 6 , they differ structurally and chemically and are known as isomers because of differing arrangements of atoms in the carbon chain. During this process, the hydroxyl group —OH of one monosaccharide combines with a hydrogen atom of another monosaccharide, releasing a molecule of water H 2 O and forming a covalent bond between atoms in the two sugar molecules.

Common disaccharides include lactose, maltose, and sucrose. Lactose is a disaccharide consisting of the monomers glucose and galactose. It is found naturally in milk. Maltose, or malt sugar, is a disaccharide formed from a dehydration reaction between two glucose molecules.

The most common disaccharide is sucrose, or table sugar, which is composed of the monomers glucose and fructose. The chain may be branched or unbranched, and it may contain different types of monosaccharides. Polysaccharides may be very large molecules. Starch, glycogen, cellulose, and chitin are examples of polysaccharides. Starch is the stored form of sugars in plants and is made up of amylose and amylopectin both polymers of glucose. Plants are able to synthesize glucose, and the excess glucose is stored as starch in different plant parts, including roots and seeds.

The starch that is consumed by animals is broken down into smaller molecules, such as glucose. The cells can then absorb the glucose. Glycogen is the storage form of glucose in humans and other vertebrates, and is made up of monomers of glucose. Glycogen is the animal equivalent of starch and is a highly branched molecule usually stored in liver and muscle cells.

Whenever glucose levels decrease, glycogen is broken down to release glucose. Cellulose is one of the most abundant natural biopolymers. The cell walls of plants are mostly made of cellulose, which provides structural support to the cell. Wood and paper are mostly cellulosic in nature. Cellulose is made up of glucose monomers that are linked by bonds between particular carbon atoms in the glucose molecule. Every other glucose monomer in cellulose is flipped over and packed tightly as extended long chains.

This gives cellulose its rigidity and high tensile strength—which is so important to plant cells. Cellulose passing through our digestive system is called dietary fiber. While the glucose-glucose bonds in cellulose cannot be broken down by human digestive enzymes, herbivores such as cows, buffalos, and horses are able to digest grass that is rich in cellulose and use it as a food source. In these animals, certain species of bacteria reside in the rumen part of the digestive system of herbivores and secrete the enzyme cellulase.

The appendix also contains bacteria that break down cellulose, giving it an important role in the digestive systems of ruminants. Cellulases can break down cellulose into glucose monomers that can be used as an energy source by the animal. Carbohydrates serve other functions in different animals. Arthropods, such as insects, spiders, and crabs, have an outer skeleton, called the exoskeleton, which protects their internal body parts.

This exoskeleton is made of the biological macromolecule chitin , which is a nitrogenous carbohydrate. It is made of repeating units of a modified sugar containing nitrogen. Thus, through differences in molecular structure, carbohydrates are able to serve the very different functions of energy storage starch and glycogen and structural support and protection cellulose and chitin. Registered Dietitian: Obesity is a worldwide health concern, and many diseases, such as diabetes and heart disease, are becoming more prevalent because of obesity.

This is one of the reasons why registered dietitians are increasingly sought after for advice. Registered dietitians help plan food and nutrition programs for individuals in various settings. They often work with patients in health-care facilities, designing nutrition plans to prevent and treat diseases.

For example, dietitians may teach a patient with diabetes how to manage blood-sugar levels by eating the correct types and amounts of carbohydrates. Dietitians may also work in nursing homes, schools, and private practices. In addition, registered dietitians must complete a supervised internship program and pass a national exam.

Those who pursue careers in dietetics take courses in nutrition, chemistry, biochemistry, biology, microbiology, and human physiology. Dietitians must become experts in the chemistry and functions of food proteins, carbohydrates, and fats.

Lipids include a diverse group of compounds that are united by a common feature. This is because they are hydrocarbons that include only nonpolar carbon-carbon or carbon-hydrogen bonds. Lipids perform many different functions in a cell.

Cells store energy for long-term use in the form of lipids called fats. Lipids also provide insulation from the environment for plants and animals. For example, they help keep aquatic birds and mammals dry because of their water-repelling nature. Lipids are also the building blocks of many hormones and are an important constituent of the plasma membrane. Lipids include fats, oils, waxes, phospholipids, and steroids.

A fat molecule, such as a triglyceride, consists of two main components—glycerol and fatty acids. Glycerol is an organic compound with three carbon atoms, five hydrogen atoms, and three hydroxyl —OH groups. In a fat molecule, a fatty acid is attached to each of the three oxygen atoms in the —OH groups of the glycerol molecule with a covalent bond. During this covalent bond formation, three water molecules are released.

The three fatty acids in the fat may be similar or dissimilar. These fats are also called triglycerides because they have three fatty acids. Some fatty acids have common names that specify their origin. For example, palmitic acid, a saturated fatty acid, is derived from the palm tree. Arachidic acid is derived from Arachis hypogaea , the scientific name for peanuts. Fatty acids may be saturated or unsaturated.

In a fatty acid chain, if there are only single bonds between neighboring carbons in the hydrocarbon chain, the fatty acid is saturated. Saturated fatty acids are saturated with hydrogen; in other words, the number of hydrogen atoms attached to the carbon skeleton is maximized. When the hydrocarbon chain contains a double bond, the fatty acid is an unsaturated fatty acid. Most unsaturated fats are liquid at room temperature and are called oils.

If there is one double bond in the molecule, then it is known as a monounsaturated fat e. Saturated fats tend to get packed tightly and are solid at room temperature. Animal fats with stearic acid and palmitic acid contained in meat, and the fat with butyric acid contained in butter, are examples of saturated fats.

Mammals store fats in specialized cells called adipocytes, where globules of fat occupy most of the cell. High concentrations of macromolecules in a solution can alter the rates and equilibrium constants of the reactions of other macromolecules, through an effect known as macromolecular crowding. All living organisms are dependent on three essential biopolymers for their biological functions: DNA , RNA and proteins.

In general, they are all unbranched polymers, and so can be represented in the form of a string. Indeed, they can be viewed as a string of beads, with each bead representing a single nucleotide or amino acid monomer linked together through covalent chemical bonds into a very long chain.

In most cases, the monomers within the chain have a strong propensity to interact with other amino acids or nucleotides. Because of the double-stranded nature of DNA, essentially all of the nucleotides take the form of Watson-Crick base pairs between nucleotides on the two complementary strands of the double-helix. In contrast, both RNA and proteins are normally single-stranded.

Therefore, they are not constrained by the regular geometry of the DNA double helix, and so fold into complex three-dimensional shapes dependent on their sequence. These different shapes are responsible for many of the common properties of RNA and proteins, including the formation of specific binding pockets , and the ability to catalyse biochemical reactions. DNA is an information storage macromolecule that encodes the complete set of instructions the genome that are required to assemble, maintain, and reproduce every living organism.

DNA and RNA are both capable of encoding genetic information, because there are biochemical mechanisms which read the information coded within a DNA or RNA sequence and use it to generate a specified protein. On the other hand, the sequence information of a protein molecule is not used by cells to functionally encode genetic information.

DNA has three primary attributes that allow it to be far better than RNA at encoding genetic information. First, it is normally double-stranded, so that there are a minimum of two copies of the information encoding each gene in every cell. Second, DNA has a much greater stability against breakdown than does RNA, an attribute primarily associated with the absence of the 2'-hydroxyl group within every nucleotide of DNA.

Third, highly sophisticated DNA surveillance and repair systems are present which monitor damage to the DNA and repair the sequence when necessary. Analogous systems have not evolved for repairing damaged RNA molecules.

Consequently, chromosomes can contain many billions of atoms, arranged in a specific chemical structure. Proteins are functional macromolecules responsible for catalysing the biochemical reactions that sustain life. The single-stranded nature of protein molecules, together with their composition of 20 or more different amino acid building blocks, allows them to fold in to a vast number of different three-dimensional shapes, while providing binding pockets through which they can specifically interact with all manner of molecules.

In addition, the chemical diversity of the different amino acids, together with different chemical environments afforded by local 3D structure, enables many proteins to act as enzymes , catalyzing a wide range of specific biochemical transformations within cells. In addition, proteins have evolved the ability to bind a wide range of cofactors and coenzymes , smaller molecules that can endow the protein with specific activities beyond those associated with the polypeptide chain alone.

RNA encodes genetic information that can be translated into the amino acid sequence of proteins, as evidenced by the messenger RNA molecules present within every cell, and the RNA genomes of a large number of viruses.

The single-stranded nature of RNA, together with tendency for rapid breakdown and a lack of repair systems means that RNA is not so well suited for the long-term storage of genetic information as is DNA.

In addition, RNA is a single-stranded polymer that can, like proteins, fold into a very large number of three-dimensional structures. A monomer joins with another monomer with the release of a water molecule, leading to the formation of a covalent bond. These types of reactions are known as dehydration or condensation reactions. When polymers are broken down into smaller units monomers , a molecule of water is used for each bond broken by these reactions; such reactions are known as hydrolysis reactions.

Dehydration and hydrolysis reactions are similar for all macromolecules, but each monomer and polymer reaction is specific to its class. Dehydration reactions typically require an investment of energy for new bond formation, while hydrolysis reactions typically release energy by breaking bonds.

Improve this page Learn More. Skip to main content. Module 3: Important Biological Macromolecules. Search for:. Visit this site to see visual representations of dehydration synthesis and hydrolysis. 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.

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. 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, 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.

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The name is descriptive of the character of this class of molecules, since they all have the general formula of a hydrated carbon. This represents a ratio of hydrogen to oxygen atoms as in water but in this case, they are attached to a carbon backbone. Monosaccharides are the most basic units of carbohydrates.

These are simple sugars, including glucose, fructose, and others. They contain between three and seven carbon atoms, have a sweet taste and are used by the body for energy. Polysaccharides are long polymers of monosaccharide sugars that are covalently bonded together.

Polysaccharides are often used to store the energy of the monosaccharide. These include starch in plants and glycogen in humans and animals.

Polysaccharides can also be used for structure in plants and other lower organisms. For example, cellulose is a large polysaccharide that is found in plant cell walls. With 3 billion DNA nucleotides per cell, that is a lot of monosaccharides in the body. Polysaccharides can be conjugated with other macromolecules. For example, complex carbohydrates can be linked with proteins or lipids to form glycoproteins and glycolipids, respectively. Very different structures can be made from a few monosaccharides arranged in different patterns and with different bonding.

This flexibility in structure can therefore be used for identification of individual cell types, since the structure of each cell type is unique. More than half of the proteins in the body, which we will discuss later in this module, have glycosylations or carbohydrate modifications. The outside of cells are covered in carbohydrates from modifications of lipids that make up the membrane; we will cover lipids in the last chapter of this section.

Carbohydrates are best know as energy storage molecules. Their primary function is as a source of energy. Cells readily convert carbohydrates to usable energy.

You will recall that molecules are a collection of atoms connected by covalent bonds. Table sugar, or sucrose, is the best-known carbohydrate. The most common carbohydrate in nature is glucose, which has the general formula.

However, the body does not need dietary carbohydrates for energy. But carbohydrates require minimal processing for use as energy.

For example, a simple enzymatic reaction converts sucrose into blood sugar, which can be used directly as a source of cellular energy. The metabolic fate of the carbohydrate will be discussed later in the course. A second function performed by carbohydrates is structure. For example, cellulose is a linear polymer of glucose that interacts with other cellulose polymers to form fibers that interact to form the basic structure of the cell wall of plants.

These cellulose polymers are undigestable and constitute the roughage. A third function of carbohydrates is cell recognition and signaling. This typically occurs with carbohydrates conjugated to other molecules, such as those found in glycoproteins carbohydrates linked to proteins and glycolipids carbohydrates linked to lipids. Because a very large number of structures can be made from a few monosaccharides simple carbohydrates , a very large number of different structures can also be made from a few simple carbohydrates, as will be seen later.

This large number of different structures can therefore be used for identification of individual cell types. Carbohydrate modifications called glycosylations are present on lipid membranes and proteins for specialized function and recognition.

Unique carbohydrate formations allow even more specificity to a protein, beyond just the amino acid code. The outer membrane of the cell is dotted with carbohydrate chains, which differ according to cell type. Thus, glycosylations are important in immune response and general cell-to-cell communication. After nucleic acids, proteins are the most important macromolecules. Structurally, proteins are the most complex macromolecules.

A protein is a linear molecule comprised of amino acids. Twenty different amino acids are found in proteins. A single protein molecule may be comprised of hundreds of amino acids. The amino acid chain can remain in its primary linear structure, but often it folds up and in on itself to form a shape. This secondary structure forms from localized interactions hydrogen bonding of amino acid side chains.

These include alpha helix and beta sheet structures. The alpha helix is dominant in hemoglobin, which facilitates transport of oxygen in blood. Secondary structures are integrated along with twists and kinks into a three-dimensional protein.

This functional form is called the tertiary structure of the protein. An additional level of organization results when several separate proteins combine to form a protein complex—called quaternary structure. Proteins perform numerous essential functions within the cell. Many proteins serve as enzymes, which control the rate of chemical reactions, and hence the responsiveness of cells to external stimuli. The Watson-Crick model attributes these ratios to the phenomenon of base pairing, in which each purine base on one strand of DNA is hydrogen-bonded to a complementary pyrimidine base in an opposing DNA strand.

DNA can assume a structure called the B form, which is a right-handed helical configuration resembling a coiled spring. The strands wind about each other, with their sugar-phosphate chains forming the coil of the helix and with their bases extending inward toward the axis of the helix. The configuration of the bases allows hydrogen bonding between opposing purines and pyrimidines.

Each of the base pairs lies in a plane at approximately right angles to the helix axis, forming a stack with the two sugar-phosphate chains coiled around the outside of the stack. In addition, DNA can exist in helical structures other than the B form. One configuration, termed the Z form, is a left-handed helical structure.

The Z form can exist in DNA sequences with alternating guanine and cytosine bases and may be functional in localized DNA regions; however, the B form is thought to predominate in most biological systems. The sequence of nucleotide pairs in the DNA determines all of the hereditary characteristics of any given organism.

The RNA, in turn, serves as a template in a process by which its encoded information is translated to determine the amino acid sequences of proteins. Each amino acid in a protein chain is specified by a triplet of nucleotides in RNA or nucleotide pairs in DNA known as a codon. The set of correlations between the amino acids and their specifying codons is called the genetic code. Each gene that codes for a protein thus contains a sequence of triplet codons that corresponds to the sequence of amino acids in the polypeptide.

This sequence of codons may be interrupted by intervening DNA sequences so that the entire coding sequence is not continuous.

In addition to coding sequences, there also exist regulatory sequences, which include promoter and operator sequences involved in initiating gene transcription and terminator sequences involved in stopping transcription.

Regulatory sequences are not necessarily made up of triplets, as are the codons. In order to study the regulation of a given gene, it is necessary to determine its nucleotide sequence. See also: Amino acid ; Genetic code ; Protein ; Transcription. In every living cell, as well as in certain viruses and subcellular organelles, the function of DNA is similar; that is, it encodes genetic information and replicates to pass this information to subsequent generations.

The nucleotide sequence of DNA in each organism determines the nature and number of proteins to be synthesized, as well as the organization of the protein-synthesizing apparatus. The entire process of gene expression, by which the flow of information proceeds from DNA to RNA to protein, remains one of the most fertile areas of molecular biological research.

The primary chemical difference between RNA and DNA is in the structure of the ribose sugar of the individual nucleotide building blocks. Another major chemical difference between RNA and DNA is the substitution of uridylic acid, which contains the base uracil 2,6-dioxypyrimidine for thymidylic acid as one of the four nucleotide building blocks. Thus, incorporation of radioactive uridine can be used as a specific measure of RNA synthesis in cells, whereas incorporation of radioactive thymidine can be used as a measure of DNA synthesis.

Further modifications of RNA structure exist, such as the attachment of various chemical groups for example, isopentenyl and sulfhydryl groups to purine and pyrimidine rings, methylation of the sugars, and folding and base pairing of sections of a single RNA strand to form regions of secondary structure.

Unlike DNA, nearly all RNA in cells is single-stranded except for regions of secondary structure and does not consist of double-helical duplex molecules. Another distinguishing characteristic of RNA is its alkaline lability.

In contrast, DNA is stable to alkali. This class comprises those molecular species that form part of the structure of ribosomes, which are components of the protein-synthesizing machinery in the cell cytoplasm. See also: Ribosomes. Messenger RNAs are those species that code for proteins. They are transcribed from specific genes in the cell nucleus, and they carry the genetic information to the cytoplasm, where their sequences are translated to determine amino acid sequences during the process of protein synthesis.

The messenger RNAs thus consist primarily of triplet codons. Most messenger RNAs are derived from longer precursor molecules that are the primary products of transcription and that are found in the nucleus.

These precursors undergo several steps known as RNA processing, eventually resulting in production of cytoplasmic messenger molecules ready for translation. See also: Cell nucleus. Transfer RNAs are small RNA molecules that possess a relatively high proportion of modified and unusual bases, such as methylinosine or pseudouridine.

Each transfer RNA molecule possesses an anticodon and an amino acid—binding site. The anticodon is a triplet complementary to the messenger RNA codon for a particular amino acid. A transfer RNA molecule bound to its particular amino acid is termed charged. The charged transfer RNAs participate in protein synthesis; through base pairing, they bind to each appropriate codon in a messenger RNA molecule and thus order the sequence of attached amino acids for polymerization. As in DNA replication, base pairing orders the sequence of nucleotides during transcription.

In RNA synthesis, uridine rather than thymidine base-pairs with adenine. The primary biological role of RNA is to direct the process of protein synthesis.

The three major RNA classes perform different specialized functions toward this end. The completed ribosome serves as a minifactory where all the components of protein synthesis are brought together during translation of the messenger RNA. The messenger RNA binds to the ribosome at a point near the initiation codon for protein synthesis. Through codon-anticodon base pairing between messenger and transfer RNA sequences, the transfer RNA molecules bearing amino acids are juxtaposed to allow formation of the first peptide bond between amino acids.

Then, the ribosome moves along the messenger RNA strand as more amino acids are added to the peptide chain. RNA of certain bacterial viruses serves a dual function.