Chapter 5 Biological Macromolecules and Lipids PDF

Chapter 5 Biological Macromolecules and Lipids Lecture Presentations by Nicole Tunbridge and © 2021 Pearson Education...

Chapter 5 Biological Macromolecules and Lipids Lecture Presentations by Nicole Tunbridge and © 2021 Pearson Education Ltd. Kathleen Fitzpatrick The Molecules of Life ▪ All living things are made up of four classes of large biological molecules: carbohydrates, lipids, proteins, and nucleic acids ▪ Macromolecules are large molecules and are complex ▪ Large biological molecules have unique properties that arise from the orderly arrangement of their atoms © 2018 Pearson Education Ltd. Figure 5.1 © 2018 Pearson Education Ltd. Figure 5.1a © 2018 Pearson Education Ltd. Concept 5.1: Macromolecules are polymers, built from monomers ▪ A polymer is a long molecule consisting of many similar building blocks ▪ The repeating units that serve as building blocks are called monomers ▪ Carbohydrates, proteins, and nucleic acids are polymers © 2018 Pearson Education Ltd. The Synthesis and Breakdown of Polymers ▪ Enzymes are specialized macromolecules that speed up chemical reactions such as those that make or break down polymers ▪ A dehydration reaction occurs when two monomers bond together through the loss of a water molecule ▪ Polymers are disassembled to monomers by hydrolysis, a reaction that is essentially the reverse of the dehydration reaction © 2018 Pearson Education Ltd. Figure 5.2 (a) Dehydration reaction: synthesizing a polymer 1 2 3 Short polymer Unlinked monomer Dehydration removes a water molecule, forming a new bond. H2O 1 2 3 4 Longer polymer (b) Hydrolysis: breaking down a polymer 1 2 3 4 Hydrolysis adds a water H2O molecule, breaking a bond. 1 2 3 H © 2018 Pearson Education Ltd. The Diversity of Polymers ▪ A cell has thousands of different macromolecules ▪ Macromolecules vary among cells of an organism, vary more within a species, and vary even more between species ▪ A huge variety of polymers can be built from a small set of monomers © 2018 Pearson Education Ltd. Concept 5.2: Carbohydrates serve as fuel and building material ▪ Carbohydrates include sugars and the polymers of sugars ▪ The simplest carbohydrates are monosaccharides, or simple sugars ▪ Carbohydrate macromolecules are polysaccharides, polymers composed of many sugar building blocks © 2018 Pearson Education Ltd. Sugars ▪ Monosaccharides have molecular formulas that are usually multiples of CH2O ▪ Glucose (C6H12O6) is the most common monosaccharide ▪ Monosaccharides are classified by ▪ The location of the carbonyl group (as aldose or ketose) ▪ The number of carbons in the carbon skeleton © 2018 Pearson Education Ltd. Figure 5.3a Aldose Ketose (Aldehyde Sugar) (Ketone Sugar) Trioses: three-carbon sugars (C3H6O3) Glyceraldehyde Dihydroxyacetone © 2018 Pearson Education Ltd. Figure 5.3b Aldose Ketose (Aldehyde Sugar) (Ketone Sugar) Pentoses: five-carbon sugars (C5H10O5) Ribose Ribulose © 2018 Pearson Education Ltd. Figure 5.3c Aldose Ketose (Aldehyde Sugar) (Ketone Sugar) Hexoses: six-carbon sugars (C6H12O6) Glucose Galactose Fructose © 2018 Pearson Education Ltd. ▪ Though often drawn as linear skeletons, in aqueous solutions many sugars form rings ▪ Monosaccharides serve as a major fuel for cells and as raw material for building molecules © 2018 Pearson Education Ltd. Figure 5.4 (a) Linear and ring forms (b) Abbreviated ring structure © 2018 Pearson Education Ltd. ▪ A disaccharide is formed when a dehydration reaction joins two monosaccharides ▪ This covalent bond is called a glycosidic linkage © 2018 Pearson Education Ltd. Figure 5.5 (a) Dehydration reaction in the synthesis of maltose 1–4 glycosidic linkage H2O Glucose Glucose Maltose (b) Dehydration reaction in the synthesis of sucrose 1–2 glycosidic linkage H2O Glucose Fructose Sucrose © 2018 Pearson Education Ltd. Polysaccharides ▪ Polysaccharides, the polymers of sugars, have storage and structural roles ▪ The architecture and function of a polysaccharide are determined by its sugar monomers and the positions of its glycosidic linkages © 2018 Pearson Education Ltd. Storage Polysaccharides ▪ Starch, a storage polysaccharide of plants, consists of glucose monomers ▪ Plants store surplus starch as granules within chloroplasts and other plastids ▪ The simplest form of starch is amylose © 2018 Pearson Education Ltd. Figure 5.6 Storage structures (plastids) containing starch granules Amylose (unbranched) in a potato tuber cell Glucose Amylopectin monomer (somewhat branched) 50 µm (a) Starch Muscle tissue Glycogen granules Glycogen (extensively stored in muscle branched) tissue Cell 1 µm wall (b) Glycogen Plant cell, surrounded Cellulose microfibrils Cellulose molecule by cell wall in a plant cell wall (unbranched) 10 µm Hydrogen bonds Microfibril 0.5 µm (c) Cellulose © 2018 Pearson Education Ltd. Figure 5.6a Storage structures (plastids) Amylose Glucose containing starch granules (unbranched) monomer in a potato tuber cell Amylopectin (somewhat branched) 50 µm (a) Starch © 2018 Pearson Education Ltd. Figure 5.6aa Storage structures (plastids) containing starch granules in a potato tuber cell 50 µm © 2018 Pearson Education Ltd. Figure 5.6b Glycogen granules Glycogen stored in muscle (extensively branched) tissue 1 µm (b) Glycogen © 2018 Pearson Education Ltd. Figure 5.6d Cell wall Plant cell, surrounded 10 µm by cell wall © 2018 Pearson Education Ltd. Animation: Polysaccharides © 2018 Pearson Education Ltd. ▪ Glycogen is a storage polysaccharide in animals ▪ Glycogen is stored mainly in liver and muscle cells ▪ Hydrolysis of glycogen in these cells releases glucose when the demand for sugar increases © 2018 Pearson Education Ltd. Structural Polysaccharides ▪ The polysaccharide cellulose is a major component of the tough wall of plant cells ▪ Like starch, cellulose is a polymer of glucose, but the glycosidic linkages differ ▪ The difference is based on two ring forms for glucose: alpha (α) and beta (β) © 2018 Pearson Education Ltd. Figure 5.7a α Glucose β Glucose (a) α and β glucose ring structures © 2018 Pearson Education Ltd. Figure 5.7b (b) Starch: 1–4 linkage of α glucose monomers (c) Cellulose: 1–4 linkage of β glucose monomers © 2018 Pearson Education Ltd. ▪ Starch (α configuration) is largely helical ▪ Cellulose molecules (β configuration) are straight and unbranched ▪ Some hydroxyl groups on the monomers of cellulose can hydrogen-bond with hydroxyls of parallel cellulose molecules © 2018 Pearson Education Ltd. ▪ Enzymes that digest starch by hydrolyzing α linkages can’t hydrolyze β linkages in cellulose ▪ The cellulose in human food passes through the digestive tract as “insoluble fiber” ▪ Some microbes use enzymes to digest cellulose ▪ Many herbivores, from cows to termites, have symbiotic relationships with these microbes © 2018 Pearson Education Ltd. ▪ Chitin, another structural polysaccharide, is found in the exoskeleton of arthropods ▪ Chitin also provides structural support for the cell walls of many fungi © 2018 Pearson Education Ltd. Figure 5.8 The structure of the chitin monomer Chitin, embedded in proteins, forms the exoskeleton of arthropods. © 2018 Pearson Education Ltd. Concept 5.3: Lipids are a diverse group of hydrophobic molecules ▪ Lipids are the one class of large biological molecules that does not include true polymers ▪ The unifying feature of lipids is that they mix poorly, if at all, with water ▪ Lipids consist mostly of hydrocarbon regions ▪ The most biologically important lipids are fats, phospholipids, and steroids © 2018 Pearson Education Ltd. Fats ▪ Fats are constructed from two types of smaller molecules: glycerol and fatty acids ▪ Glycerol is a three-carbon alcohol with a hydroxyl group attached to each carbon ▪ A fatty acid consists of a carboxyl group attached to a long carbon skeleton © 2018 Pearson Education Ltd. Figure 5.9a H H 2O Fatty acid (in this case, palmitic acid) Glycerol (a) One of three dehydration reactions in the synthesis of a fat © 2018 Pearson Education Ltd. Figure 5.9b Ester linkage (b) Fat molecule (triacylglycerol) © 2018 Pearson Education Ltd. ▪ Fats separate from water because water molecules hydrogen-bond to each other and exclude the fats ▪ In a fat, three fatty acids are joined to glycerol by an ester linkage, creating a triacylglycerol, or triglyceride ▪ The fatty acids in a fat can be all the same or of two or three different kinds © 2018 Pearson Education Ltd. ▪ Fatty acids vary in length (number of carbons) and in the number and locations of double bonds ▪ Saturated fatty acids have the maximum number of hydrogen atoms possible and no double bonds ▪ Unsaturated fatty acids have one or more double bonds © 2018 Pearson Education Ltd. Figure 5.10a (a) Saturated fat Structural formula of a saturated fat molecule Space-filling model of stearic acid, a saturated fatty acid © 2018 Pearson Education Ltd. Figure 5.10b (b) Unsaturated fat Structural formula of an unsaturated fat molecule Space-filling model of oleic acid, an unsaturated fatty acid Cis double bond causes bending. © 2018 Pearson Education Ltd. ▪ Fats made from saturated fatty acids are called saturated fats and are solid at room temperature ▪ Most animal fats are saturated ▪ Fats made from unsaturated fatty acids are called unsaturated fats or oils and are liquid at room temperature ▪ Plant fats and fish fats are usually unsaturated © 2018 Pearson Education Ltd. ▪ A diet rich in saturated fats may contribute to cardiovascular disease through plaque deposits ▪ Hydrogenation is the process of converting unsaturated fats to saturated fats by adding hydrogen ▪ Hydrogenating vegetable oils also creates unsaturated fats with trans double bonds ▪ These trans fats may contribute more than saturated fats to cardiovascular disease © 2018 Pearson Education Ltd. ▪ The major function of fats is energy storage ▪ Humans and other mammals store their long-term food reserves in adipose cells ▪ Adipose tissue also cushions vital organs and insulates the body © 2018 Pearson Education Ltd. Phospholipids ▪ In a phospholipid, two fatty acids and a phosphate group are attached to glycerol ▪ The two fatty acid tails are hydrophobic, but the phosphate group and its attachments form a hydrophilic head © 2018 Pearson Education Ltd. Figure 5.11a Choline Hydrophilic head Phosphate Glycerol Fatty acids Hydrophobic tails Kink due to cis double bond (a) Structural formula (b) Space-filling model © 2018 Pearson Education Ltd. Figure 5.11b Hydrophilic head Hydrophobic tails (c) Phospholipid symbol (d) Phospholipid bilayer © 2018 Pearson Education Ltd. ▪ When phospholipids are added to water, they self-assemble into double-layered sheets called bilayers ▪ At the surface of a cell, phospholipids are also arranged in a bilayer, with the hydrophobic tails pointing toward the interior ▪ The phospholipid bilayer forms a boundary between the cell and its external environment © 2018 Pearson Education Ltd. Steroids ▪ Steroids are lipids characterized by a carbon skeleton consisting of four fused rings ▪ Cholesterol, a type of steroid, is a component in animal cell membranes and a precursor from which other steroids are synthesized ▪ A high level of cholesterol in the blood may contribute to cardiovascular disease © 2018 Pearson Education Ltd. Figure 5.12 © 2018 Pearson Education Ltd. Concept 5.4: Proteins include a diversity of structures, resulting in a wide range of functions ▪ Proteins account for more than 50% of the dry mass of most cells ▪ Some proteins speed up chemical reactions ▪ Other protein functions include defense, storage, transport, cellular communication, movement, and structural support © 2018 Pearson Education Ltd. Figure 5.13a Enzymatic proteins Defensive proteins Function: Selective acceleration of Function: Protection against disease chemical reactions Example: Antibodies inactivate and help Example: Digestive enzymes catalyze the destroy viruses and bacteria. hydrolysis of bonds in food molecules. Antibodies Enzyme Virus Bacterium Storage proteins Transport proteins Function: Storage of amino acids Function: Transport of substances Examples: Casein, the protein of milk, is Examples: Hemoglobin, the iron-containing the major source of amino acids for baby protein of vertebrate blood, transports mammals. Plants have storage proteins in oxygen from the lungs to other parts of the their seeds. Ovalbumin is the protein of body. Other proteins transport molecules egg white, used as an amino acid source across membranes, as shown here. for the developing embryo. Transport protein Ovalbumin Amino acids for embryo Cell membrane © 2018 Pearson Education Ltd. Figure 5.13b Hormonal proteins Receptor proteins Function: Coordination of an organism’s Function: Response of cell to chemical activities stimuli Example: Insulin, a hormone secreted by Example: Receptors built into the the pancreas, causes other tissues to take membrane of a nerve cell detect signaling up glucose, thus regulating blood sugar molecules released by other nerve cells. concentration. Receptor protein High Insulin Normal Signaling blood sugar secreted blood sugar molecules Contractile and motor proteins Structural proteins Function: Movement Function: Support Examples: Motor proteins are responsible Examples: Keratin is the protein of hair, for the undulations of cilia and flagella. horns, feathers, and other skin appendages. Actin and myosin proteins are responsible Insects and spiders use silk fibers to make for the contraction of muscles. their cocoons and webs, respectively. Collagen and elastin proteins provide a fibrous framework in animal connective Actin Myosin tissues. Collagen Muscle 30 µm tissue Connective 60 µm tissue © 2018 Pearson Education Ltd. ▪ Enzymes are proteins that act as catalysts to speed up chemical reactions ▪ Enzymes can perform their functions repeatedly, functioning as workhorses that carry out the processes of life © 2018 Pearson Education Ltd. ▪ Proteins are all constructed from the same set of 20 amino acids ▪ Polypeptides are unbranched polymers built from these amino acids ▪ A protein is a biologically functional molecule that consists of one or more polypeptides © 2018 Pearson Education Ltd. Amino Acid Monomers ▪ Amino acids are organic molecules with amino and carboxyl groups ▪ Amino acids differ in their properties due to differing side chains, called R groups © 2018 Pearson Education Ltd. Figure 5.UN01 Side chain (R group) α carbon Amino Carboxyl group group © 2018 Pearson Education Ltd. Figure 5.14 Nonpolar side chains; hydrophobic Side chain (R group) Glycine Alanine Valine Leucine Isoleucine (Gly or G) (Ala or A) (Val or V) (Leu or L) (Ile or I) Methionine Phenylalanine Tryptophan Proline (Met or M) (Phe or F) (Trp or W) (Pro or P) Polar side chains; hydrophilic Serine Threonine Cysteine Tyrosine Asparagine Glutamine (Ser or S) (Thr or T) (Cys or C) (Tyr or Y) (Asn or N) (Gln or Q) Electrically charged side chains; hydrophilic Basic (positively charged) Acidic (negatively charged) Aspartic acid Glutamic acid Lysine Arginine Histidine (Asp or D) (Glu or E) (Lys or K) (Arg or R) (His or H) © 2018 Pearson Education Ltd. Polypeptides (Amino Acid Polymers) ▪ Amino acids are linked by covalent bonds called peptide bonds ▪ A polypeptide is a polymer of amino acids ▪ Polypeptides range in length from a few to more than 1,000 monomers ▪ Each polypeptide has a unique linear sequence of amino acids, with a carboxyl end (C-terminus) and an amino end (N-terminus) © 2018 Pearson Education Ltd. Figure 5.15a Peptide bond H2O © 2018 Pearson Education Ltd. Figure 5.15b Side chains (R groups) Back- bone Peptide Amino end Carboxyl end bond (N-terminus) (C-terminus) © 2018 Pearson Education Ltd. Protein Structure and Function ▪ The specific activities of proteins result from their intricate three-dimensional architecture ▪ A functional protein consists of one or more polypeptides precisely twisted, folded, and coiled into a unique shape © 2018 Pearson Education Ltd. Figure 5.16 Structural Models Target molecule (on bacterial cell surface) bound to lysozyme Space-filling model Ribbon model Wire-frame model (blue) Simplified Diagrams Insulin-producing cell in pancreas Enzyme Insulin A transparent A solid shape is shape shows the used when A simple shape is used A protein can be overall shape of structural details here to represent a represented simply the molecule are not needed. generic enzyme. as a dot. and some internal details. © 2018 Pearson Education Ltd. ▪ The sequence of amino acids determines a protein’s three-dimensional structure ▪ A protein’s structure determines how it works ▪ The function of a protein usually depends on its ability to recognize and bind to some other molecule © 2018 Pearson Education Ltd. Figure 5.17 Antibody protein Protein from flu virus © 2018 Pearson Education Ltd. Four Levels of Protein Structure ▪ The primary structure of a protein is its unique sequence of amino acids ▪ Secondary structure, found in most proteins, consists of coils and folds in the polypeptide chain ▪ Tertiary structure is determined by interactions among various side chains (R groups) ▪ Quaternary structure results when a protein consists of multiple polypeptide chains © 2018 Pearson Education Ltd. Figure 5.18a Primary Structure Amino acids 1 5 10 Amino end 30 25 20 15 35 40 45 50 Primary structure of transthyretin 55 70 65 60 75 80 85 90 95 115 110 105 100 120 125 Carboxyl end © 2018 Pearson Education Ltd. Figure 5.18aa Primary Structure Amino acids 1 5 10 Amino end 30 25 20 15 © 2018 Pearson Education Ltd. Figure 5.18ba Secondary Structure α helix Hydrogen bond β strand Hydrogen bond β pleated sheet © 2018 Pearson Education Ltd. Figure 5.18bb Tertiary Structure α helix β pleated sheet Transthyretin polypeptide © 2018 Pearson Education Ltd. Figure 5.18bc Quaternary Structure Single polypeptide subunit Transthyretin protein © 2018 Pearson Education Ltd. Figure 5.18c © 2018 Pearson Education Ltd. Figure 5.18d Hydrogen bond Hydrophobic interactions and van der Waals interactions Disulfide bridge Ionic bond Polypeptide backbone © 2018 Pearson Education Ltd. Figure 5.18e Collagen © 2018 Pearson Education Ltd. Figure 5.18f Heme Iron β subunit α subunit α subunit β subunit Hemoglobin © 2018 Pearson Education Ltd. ▪ The primary structure of a protein is its sequence of amino acids ▪ Primary structure is like the order of letters in a long word ▪ Primary structure is determined by inherited genetic information © 2018 Pearson Education Ltd. ▪ The coils and folds of secondary structure result from hydrogen bonds between repeating constituents of the polypeptide backbone ▪ Typical secondary structures are a coil called an α helix and a folded structure called a β pleated sheet © 2018 Pearson Education Ltd. ▪ Tertiary structure, the overall shape of a polypeptide, results from interactions between R groups, rather than interactions between backbone constituents ▪ These interactions include hydrogen bonds, ionic bonds, hydrophobic interactions, and van der Waals interactions ▪ Strong covalent bonds called disulfide bridges may reinforce the protein’s structure © 2018 Pearson Education Ltd. Animation: Tertiary Protein Structure © 2018 Pearson Education Ltd. ▪ Quaternary structure results when two or more polypeptide chains form one macromolecule ▪ Collagen is a fibrous protein consisting of three polypeptides coiled like a rope ▪ Hemoglobin is a globular protein consisting of four polypeptides: two α and two β subunits © 2018 Pearson Education Ltd. Animation: Quaternary Protein Structure © 2018 Pearson Education Ltd. Sickle-Cell Disease: A Change in Primary Structure ▪ A slight change in primary structure can affect a protein’s structure and ability to function ▪ Sickle-cell disease, an inherited blood disorder, results from a single amino acid substitution in the protein hemoglobin ▪ The abnormal hemoglobin molecules cause the red blood cells to aggregate into chains and to deform into a sickle shape © 2018 Pearson Education Ltd. Figure 5.19 Primary Secondary Quaternary Red Blood Cell and Tertiary Function Structure Structure Shape Structures 1 Normal β Normal Proteins do not associate subunit hemoglobin with one another; each 2 β carries oxygen. 3 Normal 4 α 5 6 7 5 µm β α 1 Sickle-cell β Sickle-cell Proteins aggregate into a subunit hemoglobin fiber; capacity to 2 carry oxygen 3 Sickle-cell β is reduced. 4 5 α 6 7 5 µm β α © 2018 Pearson Education Ltd. Figure 5.19a Secondary Primary Quaternary and Tertiary Function Structure Structure Structures 1 Normal β Normal Proteins do not associate subunit hemoglobin with one another; each 2 carries oxygen. 3 β Normal 4 α 5 6 7 β α © 2018 Pearson Education Ltd. Figure 5.19b Secondary Primary Quaternary and Tertiary Function Structure Structure Structures Sickle-cell β Sickle-cell Proteins aggregate into a 1 subunit hemoglobin fiber; capacity to 2 carry oxygen 3 β Sickle-cell is reduced. 4 α 5 6 7 β α © 2018 Pearson Education Ltd. What Determines Protein Structure? ▪ In addition to primary structure, physical and chemical conditions can affect structure ▪ Alterations in pH, salt concentration, temperature, or other environmental factors can cause a protein to unravel ▪ This loss of a protein’s native structure is called denaturation ▪ A denatured protein is biologically inactive © 2018 Pearson Education Ltd. Figure 5.20 Normal protein Denatured protein © 2018 Pearson Education Ltd. Protein Folding in the Cell ▪ It is hard to predict a protein’s structure from its primary structure ▪ Most proteins probably go through several stages on their way to a stable structure ▪ Diseases such as Alzheimer’s, Parkinson’s, and mad cow disease are associated with misfolded proteins © 2018 Pearson Education Ltd. ▪ Scientists use X-ray crystallography to determine a protein’s structure ▪ Another method is nuclear magnetic resonance (NMR) spectroscopy, which does not require protein crystallization ▪ Bioinformatics is another approach to prediction of protein structure from amino acid sequences © 2018 Pearson Education Ltd. Figure 5.21 Technique Diffracted X-rays X-ray source X-ray beam Crystal Digital X-ray diffraction detector pattern Results © 2018 Pearson Education Ltd. Concept 5.5: Nucleic acids store, transmit, and help express hereditary information ▪ The amino acid sequence of a polypeptide is programmed by a unit of inheritance called a gene ▪ Genes consist of DNA, a nucleic acid made of monomers called nucleotides © 2018 Pearson Education Ltd. The Roles of Nucleic Acids ▪ There are two types of nucleic acids ▪ Deoxyribonucleic acid (DNA) ▪ Ribonucleic acid (RNA) ▪ DNA provides directions for its own replication ▪ DNA directs synthesis of messenger RNA (mRNA) and, through mRNA, controls protein synthesis ▪ This process is called gene expression © 2018 Pearson Education Ltd. Figure 5.22_3 DNA 1 Synthesis of mRNA mRNA NUCLEUS CYTOPLASM mRNA 2 Movement of mRNA into cytoplasm Ribosome 3 Synthesis of protein Amino Polypeptide acids © 2018 Pearson Education Ltd. ▪ Each gene along a DNA molecule directs synthesis of a messenger RNA (mRNA) ▪ The mRNA molecule interacts with the cell’s protein- synthesizing machinery to direct production of a polypeptide ▪ The flow of genetic information can be summarized as DNA → RNA → protein © 2018 Pearson Education Ltd. The Components of Nucleic Acids ▪ Nucleic acids are polymers called polynucleotides ▪ Each polynucleotide is made of monomers called nucleotides ▪ Each nucleotide consists of a nitrogenous base, a pentose sugar, and one or more phosphate groups ▪ The portion of a nucleotide without the phosphate group is called a nucleoside © 2018 Pearson Education Ltd. ▪ Nucleoside = nitrogenous base + sugar ▪ There are two families of nitrogenous bases ▪ Pyrimidines (cytosine, thymine, and uracil) have a single six-membered ring ▪ Purines (adenine and guanine) have a six-membered ring fused to a five-membered ring ▪ In DNA, the sugar is deoxyribose; in RNA, the sugar is ribose ▪ Nucleotide = nucleoside + phosphate group © 2018 Pearson Education Ltd. Figure 5.23 NITROGENOUS BASES Pyrimidines Sugar-phosphate backbone 5′ end (on blue background) Cytosine (C) Thymine Uracil 5′C (T, in DNA) (U, in RNA) Purines 3′C Nucleoside Nitrogenous base Adenine (A) Guanine (G) 5′C SUGARS 1′C Phosphate 3′C 5′C group Sugar (pentose) 3′C (b) Nucleotide monomer in a polynucleotide Deoxyribose Ribose 3′ end (in DNA) (in RNA) (a) Polynucleotide, or nucleic acid (c) Nucleoside components © 2018 Pearson Education Ltd. Figure 5.23a Sugar-phosphate backbone 5′ end (on blue background) 5′C 3′C Nucleoside Nitrogenous base 5′C 1′C Phosphate 3′C 5′C group Sugar (pentose) 3′C (b) Nucleotide monomer 3′ end in a polynucleotide (a) Polynucleotide, or nucleic acid © 2018 Pearson Education Ltd. Figure 5.23b NITROGENOUS BASES Pyrimidines Cytosine (C) Thymine Uracil (T, in DNA) (U, in RNA) Purines Adenine (A) Guanine (G) (c) Nucleoside components © 2018 Pearson Education Ltd. Figure 5.23c SUGARS Deoxyribose Ribose (in DNA) (in RNA) (c) Nucleoside components © 2018 Pearson Education Ltd. Nucleotide Polymers ▪ Nucleotides are linked together by a phosphodiester linkage to build a polynucleotide ▪ A phosphodiester linkage consists of a phosphate group that links the sugars of two nucleotides ▪ These links create a backbone of sugar-phosphate units with nitrogenous bases as appendages ▪ The sequence of bases along a DNA or mRNA polymer is unique for each gene © 2018 Pearson Education Ltd. The Structures of DNA and RNA Molecules ▪ DNA molecules have two polynucleotides spiraling around an imaginary axis, forming a double helix ▪ The backbones run in opposite 5′ → 3′ directions from each other, an arrangement referred to as antiparallel ▪ One DNA molecule includes many genes © 2018 Pearson Education Ltd. ▪ Only certain bases in DNA pair up and form hydrogen bonds: adenine (A) always with thymine (T), and guanine (G) always with cytosine (C) ▪ This is called complementary base pairing ▪ This feature of DNA structure makes it possible to generate two identical copies of each DNA molecule in a cell preparing to divide © 2018 Pearson Education Ltd. ▪ RNA, in contrast to DNA, is single-stranded ▪ Complementary pairing can also occur between two RNA molecules or between parts of the same molecule ▪ In RNA, thymine is replaced by uracil (U), so A and U pair ▪ While DNA always exists as a double helix, RNA molecules are more variable in form © 2018 Pearson Education Ltd. Figure 5.24 5′ 3′ Sugar-phosphate backbones Hydrogen bonds T A Base pair joined G by hydrogen bonding C C G A T C G G G C U C A T A 3′ 5′ Base pair joined by hydrogen bonding (a) DNA (b) Transfer RNA © 2018 Pearson Education Ltd. Concept 5.6: Genomics and proteomics have transformed biological inquiry and applications ▪ Once the structure of DNA and its relationship to amino acid sequence was understood, biologists sought to “decode” genes by learning their base sequences ▪ The first chemical techniques for DNA sequencing were developed in the 1970s and refined over the next 20 years © 2018 Pearson Education Ltd. ▪ It is enlightening to sequence the full complement of DNA in an organism’s genome ▪ The rapid development of faster and less expensive methods of sequencing was a side effect of the Human Genome Project ▪ Many genomes have been sequenced, generating large sets of data © 2018 Pearson Education Ltd. Figure 5.25 © 2018 Pearson Education Ltd. ▪ Bioinformatics uses computer software and other computational tools to deal with the data resulting from sequencing many genomes ▪ Analyzing large sets of genes or even comparing whole genomes of different species is called genomics ▪ A similar analysis of large sets of proteins including their sequences is called proteomics © 2018 Pearson Education Ltd. DNA and Proteins as Tape Measures of Evolution ▪ Sequences of genes and their protein products document the hereditary background of an organism ▪ Linear sequences of DNA molecules are passed from parents to offspring ▪ We can extend the concept of “molecular genealogy” to relationships between species ▪ Molecular biology has added a new measure to the toolkit of evolutionary biology © 2018 Pearson Education Ltd.