Chapter 5 Cell Respiration and Metabolism

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Metabolism All reactions that involve energy transformations. Divided into 2 Categories: Catabolic: Release energy. Breakdown larger molecules into smaller molecules. Anabolic: Require input of energy. Synthesis of large energy-storage molecules.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Aerobic Cell Respiration Oxidation-reduction reactions: Break down of molecules for energy. Electrons are transferred to intermediate carriers, then to the final electron acceptor: oxygen. Oxygen is obtained from the blood.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycolysis Breakdown of glucose for energy in the cytoplasm. Glucose is converted to 2 molecules of pyruvic acid (pyruvate). Each pyruvic acid contains: 3 carbons 3 oxygens 4 hydrogens 4 hydrogens are removed from intermediates.

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Glycolysis Each pair of H + reduces a molecule of NAD. Produces: 2 molecules of NADH and 2 unbound H + 2 ATP Glycolysis Pathway: Glucose + 2 NAD + 2 ADP + 2 P i 2 pyruvic acid + 2 NADH and 2 ATP

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycolysis Glycolysis is exergonic. Energy released used to drive endergonic reaction: ADP + P i ATP Glucose must be activated first before energy can be obtained. ATP consumed at the beginning of glycolysis.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycolysis ATP ADP + P i P i is not released but added to intermediate molecules (phosphorylation). Phosphorylation of glucose, traps the glucose inside the cell. Net gain of 2 ATP and 2 NADH.

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Glycolysis

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lactic Acid Pathway Anaerobic respiration: Oxygen is not used in the process. NADH + H + + pyruvic acid lactic acid and NAD. Produce 2 ATP/ glucose molecule.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lactic Acid Pathway Some tissues adapted to anaerobic metabolism: Skeletal muscle: normal daily occurrence. RBCs do not contain mitochondria and only use lactic acid pathway. Cardiac muscle: ischemia

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Glycogenesis and Glycogenolysis Increase glucose intracellularly, would increase osmotic pressure. Must store carbohydrates in form of glycogen.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycogenesis: formation of glycogen from glucose. Glycogenolysis: conversion of glycogen to glucose-6- phosphate. Glucose-6-phosphate can be utilized through glycolysis.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Glycogenesis and Glycogenolysis Glucose-6-phosphate cannot leak out of the cell. Skeletal muscles generate glucose-6- phosphate for own glycolytic needs. Liver contains the enzyme glucose-6- phosphatase that can remove the phosphate group and produce free glucose.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cori Cycle Lactic acid produced by anaerobic respiration delivered to the liver. LDH converts lactic acid to pyruvic acid. Pyruvic acid converted to glucose-6- phosphate: Intermediate for glycogen. Converted to free glucose. Gluconeogenesis: conversion to non- carbohydrate molecules through pyruvic acid to glucose.

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Aerobic Respiration Aerobic respiration of glucose, pyruvic acid is formed by glycolysis, then converted into acetyl coenzyme A (acetyl CoA). Energy is released in oxidative reactions, and is captured as ATP.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Aerobic Respiration Pyruvic acid enters interior of mitochondria. Converted to acetyl CoA and 2 C0 2. Acetyl CoA serves as substrate for mitochondrial enzymes.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Acetyl CoA enters the Krebs Cycle.

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Krebs Cycle Acetyl CoA combines with oxaloacetic acid to form citric acid. Citric acid enters the Krebs Cycle. Produces oxaloacetic acid to continue the pathway. 1 GTP, 3 NADH, and 1 FADH 2 NADH and FADH 2 transport electrons to Electron Transport Cycle.

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Electron Transport Cristae of inner mitochondrial membrane contain molecules that serve as electron transport system. Electron transport chain consists of FMN, coenzyme Q, and cytochromes.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ETC Chain Each cytochrome transfers electron pairs from NADH and FADH 2 to next cytochrome. Oxidized NAD and FAD are regenerated and shuttle electrons from the Krebs Cycle to the ETC. Cytochrome receives a pair of electrons. Iron reduced, then oxidized as electrons are transferred.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ETC Chain Cytochrome a 3 transfers electrons to O 2 (final electron acceptor). Oxidative phosphorylation occurs: Energy derived is used to phosphorylate ADP to ATP.

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Coupling ETC to ATP Chemiosmotic theory: ETC powered by transport of electrons, pumps H + from mitochondria matrix into space between inner and outer mitochondrial membranes.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Coupling ETC to ATP Proton pumps: NADH-coenzyme Q reductase complex: Transports 4 H + for every pair of electrons. Cytochrome C reductase complex: Transports 4 H +. Cytochrome C oxidase complex: Transports 2 H +.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Coupling ETC to ATP Higher [H + ] in inter-membrane space. Respiratory assemblies: Permit the passage of H +. Phosphorylation is coupled to oxidation, when H + diffuse through the respiratory assemblies: ADP and P i ATP

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Coupling ETC to ATP Oxygen functions as the last electron acceptor. Oxidizes cytochrome a 3. Oxygen accepts 2 electrons. O e H + 2 H 2 0

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ATP Produced Direct phosphorylation: Glycolysis: 2 ATP Oxidative phosphorylation: 2.5 ATP produced for pair of electrons each NADH donates. 1.5 ATP produced for each pair of electrons FADH 2 donates ((activates 2 nd and 3 rd proton pumps). 26 ATP produced.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Metabolism of Lipids When more energy is taken in than consumed, glycolysis inhibited. Glucose converted into glycogen and fat.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lipogenesis Formation of fat. Occurs mainly in adipose tissue and liver. Acetic acid subunits from acetyl CoA converted into various lipids.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Metabolism of Lipids Lipolysis: Breakdown of fat. Triglycerides glycerol + fa Free fatty acids (fa) serve as blood- borne energy carriers. lipase

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Beta-oxidation Enzymes remove 2-carbon acetic acid molecules from acid end of fa. Forms acetyl CoA. Acetyl CoA enters Krebs Cycle.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Metabolism of Proteins Nitrogen is ingested primarily as protein. Excess nitrogen must be excreted. Nitrogen balance: Amount of nitrogen ingested minus amount excreted. + N balance: Amount of nitrogen ingested more than amount excreted. - N balance: Amount of nitrogen excreted greater than ingested.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Adequate amino acids are required for growth and repair. A new amino acid can be obtained by: Transamination: Amino group (NH 2 ) transferred from one amino acid to form another.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Process by which excess amino acids are eliminated. Amine group from glutamic acid removed, forming ammonia and excreted as urea.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Deamination Energy conversion: amino acid is deaminated. Ketoacid can enter the Krebs Cycle.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Use of different energy sources.