Enzymes and Metabolism

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1 PowerPoint Lecture Slides prepared by Vince Austin, University of Kentucky Enzymes and Metabolism Human Anatomy & Physiology, Sixth Edition Elaine N. Marieb 1

2 Protein Macromolecules composed of combinations of 20 types of amino acids bound together with peptide bonds Figure

3 Structural Levels of Proteins Primary amino acid sequence - lys-arg-met Secondary alpha helices or beta pleated sheets (see video) 3

4 Structural Levels of Proteins Figure 2.17a-c 4

5 Structural Levels of Proteins Tertiary superimposed folding of secondary structures Quaternary polypeptide chains linked together in a specific manner PLAY Chemistry of Life: Proteins: Tertiary Structure PLAY Chemistry of Life: Proteins: Quaternary Structure 5

6 Structural Levels of Proteins Figure 2.17d, e 6

7 Fibrous and Globular Proteins Fibrous proteins Extended and strandlike proteins Examples: keratin, elastin, collagen, and certain contractile fibers Globular proteins Compact, spherical proteins with tertiary and quaternary structures Examples: antibodies, hormones, and enzymes 7

8 Protein Denaturation Reversible unfolding of proteins due to drops in ph and/ or increased temperature Figure 2.18a 8

9 Protein Denaturation Irreversibly denatured proteins cannot refold and are formed by extreme ph or temperature changes Figure 2.18b 9

10 Characteristics of Enzymes Most are globular proteins that act as biological catalysts Holoenzymes consist of an apoenzyme (protein) and a cofactor (usually an ion ex Mg, Mb) Enzymes are chemically specific, bind to specific substrates Frequently named for the type of reaction they catalyze Enzyme names usually end in -ase Lower activation energy - catalysts, speed up reactions 10

11 Characteristics of Enzymes Figure

12 Mechanism of Enzyme Action Enzyme binds with substrate Product is formed at a lower activation energy Product is released PLAY How Enzymes Work 12

13 Mechanism of Enzyme Action Active site Amino acids 1 Enzyme (E) Substrates (s) H 2 0 Enzyme-substrate complex (E S) Free enzyme (E) 2 3 Peptide bond Internal rearrangements leading to catalysis Dipeptide product (P) Figure

14 Metabolism Metabolism all chemical reactions necessary to maintain life Cellular respiration food fuels are broken down within cells and some of the energy is captured to produce ATP Anabolic reactions synthesis of larger molecules from smaller ones Catabolic reactions hydrolysis of complex structures into simpler ones 14

15 Stages of Metabolism Energy-containing nutrients are processed in three major stages Digestion breakdown of food; nutrients are transported to tissues Anabolism and formation of catabolic intermediates where nutrients are: Built into lipids, proteins, and glycogen Broken down by catabolic pathways to pyruvic acid and acetyl CoA Oxidative breakdown nutrients are catabolized to carbon dioxide, water, and ATP 15

16 Stages of Metabolism Figure

17 Oxidation-Reduction (Redox) Reactions Oxidation occurs via the gain of oxygen or the loss of hydrogen Whenever one substance is oxidized, another substance is reduced Oxidized substances lose energy Reduced substances gain energy Coenzymes act as hydrogen (or electron) acceptors (electron carriers) Two important coenzymes are nicotinamide adenine dinucleotide (NAD + ) and flavin adenine dinucleotide (FAD) 17

18 Mechanisms of ATP Synthesis: Substrate-Level Phosphorylation High-energy phosphate groups are transferred directly from phosphorylated substrates to ADP ATP is synthesized via substrate-level phosphorylation in glycolysis and the Krebs cycle Figure 24.4a 18

19 Mechanisms of ATP Synthesis: Oxidative Phosphorylation Is carried out by the electron transport proteins in the cristae of the mitochondria Nutrient energy is used to pump hydrogen ions into the intermembrane space A steep diffusion gradient across the membrane results When hydrogen ions flow back across the membrane through ATP synthase, energy is captured and attaches phosphate groups to ADP (to make ATP) 19

20 Mechanisms of ATP Synthesis: Uses the chemiosmotic process whereby the movement of substances across a membrane is coupled to chemical reactions 20

21 Mechanisms of ATP Synthesis: Figure 24.4b 21

22 Carbohydrate Metabolism Since all carbohydrates are transformed into glucose, it is essentially glucose metabolism Oxidation of glucose is shown by the overall reaction: C 6 H 12 O 6 + 6O 2 6H 2 O + 6CO ATP + heat Glucose is catabolized in three pathways Glycolysis Krebs cycle The electron transport chain and oxidative phosphorylation 22

23 Carbohydrate Catabolism Figure

24 Glycolysis A three-phase pathway in which: Glucose is oxidized into pyruvic acid NAD + is reduced to NADH + H + ATP is synthesized by substrate-level phosphorylation Pyruvic acid: Moves on to the Krebs cycle in an aerobic pathway Is reduced to lactic acid in an anaerobic environment 24

25 Glycolysis Text 10 Step process 6C molecules are broken into 2 3C molecules 2 NADH s generated 2 ATP spent, 4ATP generated: net 2ATP Figure

26 Krebs Cycle Figure

27 Glycolysis: Phase 3 The final products are: Two pyruvic acid molecules Two NADH + H + molecules (reduced NAD + ) A net gain of two ATP molecules 27

28 Krebs Cycle: Preparatory (Intermediate) Step Occurs in the mitochondrial matrix and is fueled by pyruvic acid and fatty acids pyruvic acid has to be transferred to mitochondrion, takes energy (ATP) 28

29 Krebs Cycle: Preparatory Step Pyruvic acid is converted to acetyl CoA in three main steps: Decarboxylation Carbon is removed from pyruvic acid Carbon dioxide is released 29

30 Krebs Cycle: Preparatory Step Oxidation Hydrogen atoms are removed from pyruvic acid NAD + is reduced to NADH + H + Formation of acetyl CoA the resulting acetic acid is combined with coenzyme A, a sulfur-containing coenzyme, to form acetyl CoA 30

31 Krebs Cycle (Citric Acid cycle) OAA Figure

32 Krebs Cycle An eight-step cycle in which each acetic acid is decarboxylated and oxidized, generating: Three molecules of NADH + H + One molecule of FADH 2 Two molecules of CO 2 One molecule of ATP For each molecule of glucose entering glycolysis, two molecules of acetyl CoA enter the Krebs cycle; 2 cycles per glucose molecule PLAY Krebs Cycle 32

33 Krebs Cycle Figure

34 Mechanism of Oxidative Phosphorylation Proton pumps oxygen is the final electron acceptor Figure

35 Electron Transport Chain Food (glucose) is oxidized and the released hydrogens with electrons: Are transported by coenzymes NADH and FADH 2 Enter a chain of proteinsat the end of chain combine with molecular oxygen to form water Release energy The energy released is harnessed to make a H+ gradient which allows attachment of inorganic phosphate groups (P i ) to ADP, making ATP by oxidative phosphorylation 35

36 Mechanism of Oxidative Phosphorylation The hydrogens delivered to the chain are split into protons (H + ) and electrons The protons are pumped across the inner mitochondrial membrane by: NADH dehydrogenase (FMN, Fe-S) Cytochrome b-c 1 Cytochrome oxidase (a-a 3 ) The electrons are shuttled from one acceptor to the next 36

37 Mechanism of Oxidative Phosphorylation Electrons are delivered to oxygen, forming oxygen ions Oxygen ions attract H + to form water H + pumped to the intermembrane space: Diffuses back to the matrix via ATP synthase Releases energy to make ATP PLAY InterActive Physiology : Muscular System: Muscle Metabolism 37

38 Mechanism of Oxidative Phosphorylation Figure

39 Electronic Energy Gradient The transfer of energy from NADH + H + and FADH 2 to oxygen releases large amounts of energy This energy is released in a stepwise manner through the electron transport chain 39

40 Electronic Energy Gradient The electrochemical proton gradient across the inner membrane: Creates a ph gradient Generates a voltage gradient These gradients cause H + to flow back into the matrix via ATP synthase PLAY Electron Transport 40

41 Electronic Energy Gradient Figure

Ch. 9 Cell Respiration. Title: Oct 15 3:24 PM (1 of 53)

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