The Chemical Building Blocks of Life Chapter 3 Biochemistry • The study of the Chemistry of Life • 4 Classes of Biological Molecules 1.Carbohydrates 2.Nucleic Acids 3.Proteins 4.Lipids • The Classes are determined by the proportions of C, H, O in the molecule • We will distinguish the structures and functions of each in living cells 38 Biomolecules • Organic Molecules – Composed of Carbon and Hydrogen – Elements Nitrogen, Oxygen, Phosphate, Sulfur also included – These six elements compose 98.5% of body weight (Saladin, 5th ed.) • Some Inorganic molecules are incorporated as well – The Heme group in Hemoglobin contains Fe, for example – Trace elements 40 Biological Molecules Biological molecules are composed of: 1. A Central Carbon or Carbon Chain 2. Functional Groups 4 Organic Chemistry • The carbon chain backbone of a molecule or Carbon Skeleton CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH3 • Recall: Carbon makes 4 covalent bonds 41 Functional Groups • Functional Groups are specific combinations of bonded atoms attached to a Carbon Skeleton • The Functional Groups determine the chemistry of the molecule • Functional groups behave in chemically predictable ways 42 7 Biological Molecules • Biological molecules are typically Marcomolecules - Very large molecules with high molecular weights - DNA over a meter long • Macromolecules are Polymers assembled from smaller Monomers - Monomers - small, identical or similar subunits - Polymers - covalently bonded monomers 8 Monomers and Polymers • Proteins • Amino Acid monomers polymerize to form proteins • Nucleotides • Nucleotide monomers polymerize to form DNA and RNA Macromolecules • Carbohydrates • Simple sugar monomers polymerize to form • complex sugars Monosaccharides polymerize to form disaccharides, polysaccharides Polymerization • The joining monomers to form a polymer • Dehydration Synthesis - the chemical reaction for how living cells form polymers • A bond is formed between monomers and water is produced as a product of the reaction • As the name implies, water is lost during the reaction • Also known as Condensation 2-66 Dehydration Synthesis • A hydroxyl (-OH) group is removed from one monomer, and a hydrogen (H+) from another • A new bond is formed between the monomers • Water is released as a by-product Dehydration Synthesis • Monomers covalently bond together to form a polymer with the removal of a water molecule – A hydroxyl group is removed from one monomer and a hydrogen from the next Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Dimer Monomer 1 Monomer 2 O OH HO H+ + OH– H2O (a) Dehydration synthesis Figure 2.15a 2-67 Hydrolysis • The reaction for the separation of joined monomers • “Splitting with water” • Opposite of dehydration synthesis – a water molecule ionizes into –OH and H+ – the covalent bond linking one monomer to the other is broken – the –OH is added to one monomer – the H+ is added to the other Hydrolysis • Splitting a polymer (lysis) by the addition of a water molecule (hydro) – a covalent bond is broken • All digestion reactions consists of hydrolysis reactions Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Dimer Monomer 1 Monomer 2 OH O H2O HO H+ + OH– (b) Hydrolysis Figure 2.15b 2-68 Biological Molecules 15 1. Carbohydrates The Saccharides (Sugars) 2 1. Carbohydrates Carbohydrates • Sugars, Starches, Fibers • Names of carbohydrates often built from: – word root ‘sacchar-’ – the suffix ’-ose’ – both mean ‘sugar’ or ‘sweet’ • monosaccharide or glucose 2-69 1. Carbohydrates • Carbohydrates are composed of carbon backbones with Hydroxyl Groups and a Carboxyl Group – R-OH – R-COOH • The carbon backbone may be a in straight line or a closed ring of carbon atoms • Polar and therefore Hydrophilic Molecules 1. Carbohydrates 60 1. Carbohydrates • The Proportions of C, H, and O for Carbohydrates follow the General Formula: CnH2nOn – n = number of carbon atoms – for glucose, n = 6, so formula is C6H12O6 – 2:1 ratio of hydrogen to oxygen 1. Carbohydrates • Names of carbohydrates: – Carbohydrates are classified for the number of carbon atoms in the carbon backbone • Pentose, Hexose – Many carbohydrates have common names • Glucose, Fructose, Sucrose, Lactose Carbohydrate Structure • Numbering the C’s • Carbohydrates are classified by the number of Carbon atoms they contain • For Example: Ribose is a pentose sugar because it contains 5 carbon atoms Glucose is a hexose sugar because it contains 6 carbon atoms • Many Carbohydrates have informal names that do not provide information about the molecule 5 Carbohydrate Structure • Numbering the Carbons • Numbering System allows the molecules to be described efficiently • The Carbons of Carbohydrates are numbered • For Example: • Describing locations of covalent bonds • Ribose vs 2’ Deoxy-ribose 6 Carbohydrates 24 Carbohydrates 25 Carbohydrate Structure Numbering the Carbons Ribose vs. 2 Deoxyribose • Ribose • 2’ Deoxyribose 7 1. Carbohydrates 1. Monosaccharides 2. Disaccharides 3. Polysaccharides 104 27 Carbohydrate Classification 1. Monosaccharides • Simple Sugars • Are not hydrolyzed into smaller carbohydrates 2. Disaccharides • On hydrolysis, are cleaved into two monosaccharides 3. Polysaccharides • Are Hydrolyzed to more than 10 monosaccharides 8 9 1. Monosaccharides a. Structure • There are over 200 different monosaccharides • Monosaccharides differ in the number of carbon atoms they contain in the C-C backbone (Ex. hexose vs. pentose) • Monosaccharides also differ in their STEREOCHEMISTRY – the 3 dimensional 10 shape of the molecule Monosaccharides differ in their Stereochemistry - 3D shape Pentose C5H10O5 Hexose C6H12O6 67 Monosaccharides are Isomers Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Isomers – molecules with the same chemical formula, but different structures • 3 important monosaccharides – glucose, galactose and fructose Glucose CH2OH H HO Galactose HO H • Same molecular formula - C6H12O6 – isomers O H H OH H H OH OH CH2OH O H OH H H OH H OH Fructose O HOCH2 H OH H HO OH H Figure 2.16 CH2OH 2-70 Carbohydrates 33 Carbohydrates 34 Chiral Molecules • Isomers that are mirror images of each other 35 1. Monosaccharides b. Functions • Energy Source - Are efficiently oxidized for energy - The C-H bonds are high in energy - The C-H bonds are oxidized • Most Important example: - Glucose in Cellular Respiration C6H12O6 + 6 O2 Glucose Oxygen 6 H2O + 6 CO2 + Energy Water Carbon Dioxide 13 2. Disaccharides a. Structure Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Sugar molecule composed of 2 monosaccharides Sucrose CH2OH O H H OH H H Lactose – sucrose - table sugar HO • glucose + fructose H • glucose + galactose – maltose - grain products • glucose + glucose H HO CH2OH OH OH CH2OH H H OH O H OH OH O OH H H H H – lactose - sugar in milk H O HO • 3 important disaccharides CH2OH O H H OH H O H CH2OH Maltose CH2OH CH2OH O H H OH H HO H OH H O H O H OH OH H H H Figure 2.17 OH 2-71 2. Disaccharides Polymerization • Monosaccharides are joined together into chains through a Dehydration Reaction • A dimer of two monosaccharides is formed • Water is lost in the polymerization reaction 16 Dehydration Synthesis Glucose + Fructose = Maltose + H2O Glucose + Glucose = Maltose + H2O 39 Dehydration Reaction •Carbon 1 on the left glucose exchanges its bond with the hydroxyl group for a bond with the oxygen of the hydroxyl group on carbon 4 of the glucose on the right (OH is released) •The oxygen of hydroxyl group of carbon 4 exchanges its bond with H for a bond with carbon 1 (H is released) 6 5 1 4 3 4 11 1 4 2 H2O • OH + H yields H2O 17 2. Disaccharides Hydrolysis Reaction • Chains of Carbohydrates are cleaved into smaller chains and monosaccharides through Hydrolysis Reactions • As the name implies, the complex carbohydrates are “cleaved by water” 18 2. Disaccharides Hydrolysis Reaction Maltose + H2O = Glucose + Glucose + H2O 19 3. Polysaccharides a. Structure 1. Multiple Monosaccharides linked together b. Functions 1. Structural Molecules 2. Signaling Molecules 3. Energy Storage 20 3. Polysaccharides • 3 Important Polysaccharides: 1. Glucose 2. Starch 3. Cellulose 44 Glycogen • Glycogen: energy storage polysaccharide in animals – long, branching chains of glucose monomers – made by cells of liver, muscles, brain, uterus, and vagina – liver produces glycogen when glucose blood level is high, then breaks it down when needed to maintain blood glucose levels – muscles store glycogen for own energy needs – uterus uses glycogen to nourish embryo Glycogen Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CH2OH O O O O CH2OH O CH2OH O CH2 O (a) CH2OH O O CH2OH O O O O O (b) Figure 2.18 2-73 Glycogen 47 Glycogen Inclusions in a Liver Cell Stryer's Biochemistry Fig. 23-2 82 3. Polysaccharides • Starch: energy storage polysaccharide in plants – only significant digestible polysaccharide in the human diet • Cellulose: structural molecule of plant cell walls - fiber in our diet 3. Polysaccharides b. Function 1. Structural Molecules Cellulose - plant cell walls Chitin – Fungi cell walls Peptidoglycan - Bacterial cell walls 22 Carbohydrates 51 Carbohydrates 52 Carbohydrates 53 Carbohydrate Functions 1.Structural: • Conjugated carbohydrates – covalently bound to lipid or protein – glycolipids • external surface of cell membrane – glycoproteins • external surface of cell membrane • mucus of respiratory and digestive tracts – proteoglycans (mucopolysaccharides) • • • • gels that hold cells and tissues together forms gelatinous filler in umbilical cord and eye joint lubrication tough, rubbery texture of cartilage Glycoproteins on Cell Surface Viral Bioinformatics Resource Center athena.bioc.uvic.ca/.../copy9_of_sample/surface 24 3. Polysaccharides Function 2. Signaling Molecules • GLYCOPROTEINS – Carbohydrates bound to proteins – Example: Red Blood Cell Groups – Used by the Immune System to identify cells • Antigenic – Are detected by the immune system and can cause an immune response 23 3. Polysaccharides b. Functions 3.Energy Storage – Excess glucose stored as Glycogen – Hydrolyzed to Glucose as needed 2-74 2. Nucleic Acids • DNA = Deoxyribonucleic Acid • RNA = Ribonucleic Acid • Function to store, transport, and control hereditary information 149 2. Nucleic Acids • DNA (deoxyribonucleic acid) – constitutes genes • instructions for synthesizing all of the body’s proteins • transfers hereditary information from cell to cell and generation to generation • RNA (ribonucleic acid) – 3 types – – – – messenger RNA, ribosomal RNA, transfer RNA 70 to 10,000 nucleotides long carries out genetic instruction for synthesizing proteins assembles amino acids in the right order to produce proteins 2-110 2. Nucleic Acids • The Nucleic Acids are some of the largest organic compounds found in organisms • Nucleic Acids are composed of Carbon, Hydrogen, Oxygen, Nitrogen and Phosphorous atoms • Nucleic Acids are components of DNA and RNA – the molecules responsible for the storage, transport and regulation of hereditary information 4-2 2. Nucleic Acids • Nucleotides are the uilding blocks of bucleic acids (DNA and RNA) and ATP • 3 components of nucleotides 1. Nitrogenous base 2. Ribose Sugar (monosaccharide) 3. Phosphate groups 2-104 2. Nucleic Acids 62 The Nitrogenous Bases of Nucleotides • There are 5 different Nitrogenous Bases to choose from when building Nucleic Acids: 155 The Nitrogenous Bases of Nucleotides • DNA is composed of • RNA is composed of the Nitrogenous Bases: the Nitrogenous Thymine, Cytosine, Bases: Uracil, Adenine, and Cytosine, Adenine, Guanine and Guanine 156 Nitrogenous Bases of DNA Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Purines O • Purines - double ring NH2 C – Adenine (A) – Guanine (G) N C N C CH C HN C C H N NH NH C C N CH N NH2 Adenine (A) Guanine (G) Pyrimidines • Pyrimidines - single ring H C CH3 C HC C N N H – Cytosine (C) – Thymine (T) • DNA bases - ATCG • RNA bases - AUCG NH2 O C HC C NH N H O Cytosine (C) C O Thymine (T) O HN C O (b) C N H CH CH Uracil (U) Figure 4.1b 4-5 The Nitrogenous Bases 66 The Ribose Sugar of Nucleotides The Nucleotides of DNA • The name, Deoxyribonucleic Acid, tells us the structure of the ribose sugar in the Nucleotides of DNA The Nucleotides of RNA • The name, Ribonucleic acid, tells us the structure of the ribose sugar in the RNA Nucleotides • It lacks a hydroxyl group at C2 153 The Phosphate Group of Nucleotides • Both The Phosphate Group and the Nitrogenous Base attach to the central Ribose Sugar • The Phosphate Group Attaches at the 5’ Carbon of the Nucleotide • The Nitrogenous Base Attaches at the 1’ Carbon of the Nucleotide • The Phosphate Group is important in forming the “Backbone” of the Nucleic Acid Molecule 157 The Phosphate Group of Nucleotides 158 Polymerization of Nucleotides to Make Nucleic Acids (DNA and RNA) • Nucleotides are covalently bound together into long strands through a Dehydration Reaction • The Phosphate of one Nucleotide is bound to the Ribose Sugar of an adjacent nucleotide • These Phosphate-Ribose bonds form the backbones of the Nucleic Acid Molecules 159 The Backbone is formed by multiple C3C5 phospho-ribose linkages 160 The Backbone is formed by multiple C3C5 phospho-ribose linkages 161 DNA Molecular Structure • DNA is a long threadlike molecule with uniform diameter, but varied length Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Adenine NH2 N HC – total length of 2 meters – average DNA molecule 2 inches long • 46 DNA molecules in the nucleus of most human cells (Chromosomes) N H C C C N CH N O HO P O OH O CH2 H H OH Phosphate H H H Deoxyribose (a) Figure 4.1a 4-4 DNA Molecular Structure 74 DNA Double Helix Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Two DNA strands are united by hydrogen bonds to form the double-helix (b) T • DNA base pairing – – C G A – T with 2 hydrogen bonds C – G with 3 hydrogen bonds T • Law of Complementary Base Pairing – one strand determines base sequence of other – One strand serves as the template for the complementary strand G C A G C Hydrogen bond Sugar–phosphate backbone Sugar–phosphate backbone (c) Figure 4.2 partial 4-7 Complementary Base Pairing • To form the Double Stranded structure of DNA, two polynucleotide strands pair up through hydrogen bonds between specific Nitrogenous Bases: • In DNA, Adenine pairs with Thymine via 2 Hydrogen bonds • In DNA, Guanine pairs with Cytosine via 3 Hydrogen Bonds • In RNA, Adenine pairs with Uracil via 2 Hydrogen Bonds • A to T with two H-bonds, G to C with 3 H-bonds 163 Complementary Base Pairing 164 Fig. 3.16-1 Nucleic Acids 79 Nucleic Acids RNA • Contains ribose instead of deoxyribose • Contains uracil instead of thymine • Single polynucleotide strand • Functions: -Read the genetic information in DNA -Direct the synthesis of proteins 80 Fig. 3.16-2 Nucleic Acids Other nucleotides • ATP: adenosine triphosphate -primary energy currency of the cell • NAD+ and FAD: electron carriers for many cellular reactions 82 The Chemical Building Blocks of Life Chapter 3 Sec. 2 Proteins and Lipids 3. Proteins • Protein - a polymer of amino acids • Amino acids - the monomers of proteins • 20 Amino acids are used to construct proteins • Peptide Bonds form between adjacent amino acids 2-85 Protein Functions 1. Structure – keratin – tough structural protein • gives strength to hair, nails, and skin surface – collagen – durable protein contained in deeper layers of skin, bones, cartilage, and teeth 2. Communication – some hormones and other cell-to-cell signals – receptors to which signal molecules bind • ligand – any hormone or molecule that reversibly binds to a protein 3. Membrane Transport – channels in cell membranes that governs what passes through – carrier proteins – transports solute particles to other side of membrane 2-94 – turn nerve and muscle activity on and off Protein Functions 4. Catalysis – enzymes 5. Recognition and Protection – immune recognition – antibodies – clotting proteins 6. Movement – motor proteins - molecules with the ability to change shape repeatedly 7. Cell adhesion – proteins bind cells together – immune cells to bind to cancer cells – keeps tissues from falling apart 2-95 Amino Acid Structure •A Central carbon with 4 attachments: 1.amino group (NH2) 2.carboxyl group (COOH) 3.radical group (R group) 4.hydrogen • Properties of amino acid determined by -R group Amino Acid Structure • By definition, all amino acids have the amine and carboxyl groups in common • Amino differ in the side chains • Different side chains give amino acids different chemical properties (for example, some amino acids are hydrophobic, some are hydrophilic) Page 46 Representative Amino Acids Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Some nonpolar amino acids Some polar amino acids Methionine H Cysteine H H N N C H CH2 CH2 S C H CH3 O OH O Tyrosine H SH H H C OH Arginine N H N CH2 OH H C O CH2 C C H H C NH2+ (CH2)3 O C NH2 C OH NH Figure 2.23a OH (a) • Note: they differ only in the R group 2-86 Proteins The structure of the R group dictates the chemical properties of the amino acid. Amino acids can be classified as: 1. nonpolar 2. polar 3. charged 4. aromatic 5. special functions (acidic, basic) 91 Fig. 3.20 Fig. 3.20-1 Fig. 3.20-2 Fig. 3.20-3 Fig. 3.20-4 Fig. 3.20-5 Peptides • Peptide – any molecule composed of two or more amino acids joined by peptide bonds • Peptide Bond – joins the amino group of one amino acid to the carboxyl group of the next – formed by dehydration synthesis • Peptides named for the number of amino acids – – – – dipeptides have 2 oligopeptides have fewer than 10 to 15 polypeptides have more than 15 proteins have more than 50 2-87 Amino Acid Polymerization 99 The Formation of a Peptide Bond Dehydration Reaction: The loss of water The Peptide Bond • Amino acids are joined together into polypeptide chains through a DEHYDRATION REACTION • Similarly, Polypeptide chains are cleaved apart through a HYDROLYSIS REACTION Hydrolysis Reaction Hydrolysis Reaction: The Bond is Cleaved with water H2O Find the Peptide Bond Peptide Bond Terminal Animo Group Side Chain Carboxyl Group Peptide Bond Amino Group Side Chain Protein Structure and Shape • Protein properties and functions depend on Protein Conformation • Conformation – unique three dimensional shape of protein crucial to function • Because of unique conformations, proteins are very specific to their functions • Protein conformation depends on the environment 2-89 Protein Structure and Shape • Four Level of Protein Structure 1.Primary structure 2.Secondary structure 3.Tertiary structure 4.Quaternary structure 2-89 Protein Structure and Shape 1. Primary structure – protein’s sequence amino acid – encoded in the genes 2-89 Fig. 3.22-1 Protein Structure and Shape 2. Secondary structure – coiled or folded shape held together by hydrogen bonds – hydrogen bonds between slightly negative C=O and slightly positive N-H groups • Two secondary structure motifs: – Alpha Helix – springlike shape – Beta Helix – pleated, ribbonlike shape 2-89 Fig. 3.21a Fig. 3.22-2 Fig. 3.22-3 Protein Structure and Shape 3. Tertiary structure – further bending and folding of proteins into globular and fibrous shapes – further folding due to Hydrogen bonding or other R group interactions within the chain, hydrophobic/hydrophilic interactions • globular proteins –compact tertiary structure well suited for proteins embedded in cell membrane and proteins that must move about freely in body fluid • fibrous proteins – slender filaments better suited for roles as in muscle contraction and strengthening the skin 2-89 Fig. 3.21a Fig. 3.21b Fig. 3.21c Fig. 3.21d Fig. 3.21e Fig. 3.22-4 Protein Structure and Shape 3. Tertiary structure • Tertiary Structure of polypeptides forms Domains • Domains are 3D functional regions of a polypeptide strung together on the polypeptide chain 2-89 Fig. 3.23 Protein Structure and Shape • Quaternary structure – associations of two or more separate polypeptide chains – the chains are not covalently bonded 2-89 Fig. 3.22 Conjugated Proteins • Proteins that contain a non-amino acid moiety called a prosthetic group • Hemoglobin contains four complex iron containing rings called a heme moieties Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 2.24 (4) Beta chain Alpha chain Association of two or more polypeptide chains with each other Heme groups Alpha chain Quaternary structure Beta chain 2-92 Structure of Proteins Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Amino acids Primary structure Peptide bonds Tertiary structure Sequence of amino acids joined by peptide bonds Folding and coiling due to interactions among R groups and between R groups and surrounding water C C Alpha helix Beta sheet C C C C C C Chain 1 Alpha helix or beta sheet formed by hydrogen bonding C C Secondary structure Beta chain C C Chain 2 Alpha chain Heme groups Alpha chain Quaternary structure Association of two or more polypeptide chains with each other Beta chain Figure 2.24 2-90 Proteins • Protein folding is aided by Chaperone Proteins • Endoplasmic Reticulum, Golgi Appartus Fig. 3.24 127 Protein Denaturation • A change in the shape of a protein, usually causing loss of function • Caused by changes in the protein’s environment - pH - temperature - concentration • Protein ‘unfolding’ - looses layers of structure as conditions deviate - Quaternary Tertiary Secondary Primary 2-91 Protein Denaturation 129 Protein ‘Renaturation’ • Protein conformation can be restored if conditions are returned to normal Secondary Tertiary Quaternary • Conformation cannot be restored if primary structure is lost • Because protein function depends on conformation, proteins work best in their specific environments 2-91 Fig. 3.26 Protein ‘Renaturation’ Enzymes • Enzymes - special class of proteins that functions as biological catalysts – facilitate chemical reactions • The Rules to be an Enzyme 1. It is a protein molecule that speeds up a chemical reaction 2. Enzymes are not changed during the reaction 3. Enzymes can be re-used many times 2-96 Enzymes • Enzymes - proteins that function as biological catalysts – facilitate chemical reactions – regulate chemical reactions – permit reactions to occur rapidly at normal body temperature • The Rules to be an Enzyme 1. It is a protein molecule that speeds up a chemical reaction 2. Enzymes are not changed during the reaction 3. Enzymes can be re-used many times • Naming Convention – named for enzyme substrate with -ase as the suffix • amylase enzyme digests amylose (a starch) 2-96 Enzyme Structure • Substrate - substance an enzyme acts upon • Active Site - area of an enzyme where the chemical activity takes place – The active site is specifically shaped to bind to a certain substrate – The active site is usually a cleft or indented area of a protein – The active site is lined with various R groups that provide the chemical activity 143 How Enzymes Work: • Enzymes Lower the Activation Energy energy needed to get reaction started – enzymes facilitate molecular interaction • Enzymes lower the Activation Energy by: 1. Bringing the chemically active portions (functional groups, for example) of Substrates together 2. Destabilizing Substrates, making them more prone to break or form bonds 3. Decreasing Entropy – Enzymes hold substrates in place, increasing the chance that chemical reactions will occur Enzymes and Activation Energy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Free energy content Activation energy Activation energy Net energy released by reaction Energy level of reactants Net energy released by reaction Energy level of products Time (a) Reaction occurring without a catalyst Time (b) Reaction occurring with a catalyst Figure 2.26a, b 2-97 Enzyme Structure and Action • Enzyme/Substrate Complex: E+S ES EP E+P 1. The Enzyme and the Substrate come together (E+S) 2. The Enzyme/Substrate Complex is formed (ES) 3. The Enzyme’s Substrate is changed to the Enzyme’s Product in the active site of the enzyme (EP) 4. The Enzyme and Product Separate (E+P) 5. The Enzyme is free to bind to another Substrate Enzyme Structure and Action • Substrate approaches active site on enzyme molecule • Substrate binds to active site forming enzyme-substrate complex – highly specific fit –’lock and key’ • enzyme-substrate specificity • Enzyme breaks covalent bonds between monomers in substrate • adding H+ and OH- from water – Hydrolysis • Reaction products released – glucose and fructose • Enzyme remains unchanged and is ready to repeat the process 2-98 Enzymatic Reaction Steps Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sucrose (substrate) 1 Enzyme and substrate O Active site Sucrase (enzyme) 2 Enzyme–substrate complex O Glucose 3 Enzyme and reaction products Fructose Figure 2.27 2-99 Enzymatic Action • Reusability of enzymes – enzymes are not consumed by the reactions • Astonishing speed – one enzyme molecule can consume millions of substrate molecules per minute • Factors that change enzyme shape – pH and temperature – alters or destroys the ability of the enzyme to bind to substrate – enzymes vary in optimum pH • salivary amylase works best at pH 7.0 • pepsin works best at pH 2.0 – temperature optimum for human enzymes – body temperature (37 degrees C) 2-100 The Allosteric Site • The allosteric site is another binding area of the enzyme • The allosteric site binds a substance other than the substrate • Binding at the allosteric site can induce a change in the shape of the protein and affect the active site • *Noncompetitive inhibitors bind to allosteric sites Conformational Change • The change in the shape of the protein induced by binding at an allosteric site is known as a CONFORMATIONAL CHANGE 29 Protein Specificity • The Quaternary Shape of a Protein gives the Active Site Specificity • • • • Specific Receptors Specific Antigens Specific Antibodies Specific Substrates • Specificity is important for enzyme action and function Protein Specificity • Lock and Key Hypothesis: • The Substrates of Protein Active Sites fit like a key fits into a lock • Induced Fit Hypothesis: • The Active Site of a Protein changes shape as a it binds to its substrate to create a very specific fit Conformational Change Example: Hemoglobin • Hemoglobin is the protein in Red Blood Cells that carries Oxygen • One molecule of Hemoglobin has four active sites – each active site can bind to one molecule of oxygen • Hemoglobin undergoes conformational changes at each of its oxygen binding sites as molecules of oxygen bind Hemoglobin Conformational Change Example: Hemoglobin • As each oxygen binding site binds a molecule of oxygen, a conformational change is induced to the rest of the oxygen binding sites • With the binding of every O2, the other O2 binding sites have a weaker attraction for O2 • How is this important physiologically? Cofactors and Coenzymes • Cofactors – about 2/3rds of human enzymes require a nonprotein cofactor – inorganic partners (iron, copper, zinc, magnesium and calcium ions) – some bind to enzyme and induces a change in its shape, which activates the active site – essential to function • Coenzymes – organic cofactors derived from water-soluble vitamins (niacin, riboflavin) – they accept electrons from an enzyme in one metabolic 2-101 pathway and transfer them to an enzyme in another Coenzyme NAD+ Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Aerobic respiration Glycolysis Pyruvic acid Glucose ADP + Pi e– NAD+ e– ATP Pyruvic acid CO2 + H2O Figure 2.28 • NAD+ transports electrons from one metabolic pathway to another 2-102 Metabolic Pathways • Chain of reactions, with each step usually catalyzed by a different enzyme • ABCD • A is initial reactant, B+C are intermediates and D is the end product • Regulation of metabolic pathways – activation or deactivation of the enzymes – cells can turn on or off pathways when end products are needed and shut them down when the end products are not needed 2-103 4. Lipids • Lipid molecules are composed of Carbon, Hydrogen, and Oxygen atoms • The proportion of oxygen is much lower in lipids than it is in carbohydrates • A high proportion of nonpolar C – H bonds causes the molecule to be hydrophobic • Lipids are insoluble in water 29 Lipids • Two main categories of lipids 1. Fats (Triglycerides) 2. Phospholipids 134 152 1. Triglycerides • Molecule for energy storage – store twice as much energy as carbohydrates • Animal fats are are solid at room temperature - Adipose tissue, waxes • Plant fats (oils) are liquid at room temperature 153 1. Triglycerides • Composed of 2 Parts: a. Glycerol Molecule b. Three Fatty Acids (tri) • 3 fatty acids covalently bonded to a glycerol molecule – each bond formed by dehydration synthesis – broken down by hydrolysis 2-78 a. Glycerol • Glycerol is a 3 carbon molecule with 3 hydroxyl groups • One, two, or three fatty acids can bind at the locations of the Hydroxyl Groups to form a lipid 95 b. Fatty Acids • Chain of 4 to 24 carbon atoms – carboxyl (acid) group on one end, methyl group on the other and hydrogen bonded along the side H H H H H H H H H H H H H H H C C C C C C C C C C C C C C C H H H H H H H H H H H H H H H O C H HO Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 2.19 2-77 Fatty Acids • Classes of Fatty Acids a. Saturated - carbon atoms saturated with hydrogen b. Unsaturated - contains C=C bonds without hydrogen c. Polyunsaturated – contains many C=C bonds Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. O HO C H H H H H H H H H H H H H H H C C C C C C C C C C C C C C C H H H H H H H H H H H H H H H Palmitic acid (saturated) CH3(CH2)14COOH Figure 2.19 H 2-77 Fatty Acids a. Saturated Fatty Acids - carbon backbone saturated with hydrogen - Contains C-C Single Bonds only Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. O HO C H H H H H H H H H H H H H H H C C C C C C C C C C C C C C C H H H H H H H H H H H H H H H Palmitic acid (saturated) CH3(CH2)14COOH Figure 2.19 H 2-77 Saturation A Saturated Fatty Acid 89 Fatty Acids b.Unsaturated Fatty Acids - contains C=C bonds, therefore fewer hydrogens c.Polyunsaturated - contains many C=C bonds Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. O HO C H H H H H C C C C C C H H H H H H H H H C C C H H C H H H H H C C C C C H H H H H Figure 2.19 H 2-77 Saturation • An Unsaturated Fatty Acid 90 Examples of Fatty Acids 87 Saturation • The Saturation or Unsaturation of the Fatty Acids affects the properties of the lipid • Unsaturations put “kinks” in the fatty acids • Kinks in the fatty acids prevent them from stacking together, making them less stable solids • Unsaturated Fats are usually liquids at room temperature – plant fats (oils) 92 Saturation • Saturated fats are not kinked • They stack together making the lipid more stable solids • Saturated Fats are usually solid at room temperature – animal fats and waxes 93 Saturation • Saturated Fatty Acids • Unsaturated Fatty Acids 94 Triglyceride Synthesis Glycerol + 3 Fatty Acids A Triglyceride + 3H2O A Dehydration Rxn. 96 Saturated Fats 167 Unsaturated Fats 168 2. Phospholipids • Similar to triglycerides except that one fatty acid is replaced by a phosphate group Phospholipids • Phospholipids are Amphiphilic molecules – fatty acid “tails” are hydrophobic – phosphate “head” is hydrophilic Polar Head Group Nonpolar Hydrocarbon Tail 101 Phospholipids • Because of Hydrophobic/ Hydrophilic Interactions, phospholipids spontaneously form micelles or lipid bilayers in water • These structures cluster the hydrophobic tail regions of the phospholipid toward the inside and leave the hydrophilic head regions exposed to the water environment. • Lipid bilayers are the basis of biological membranes 171 Micelle 172 Phospholipid Bilayer 173