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Chapter 5

Chapter 5. Cell Respiration and Metabolism. 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.

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Chapter 5

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  1. Chapter 5 Cell Respiration and Metabolism

  2. 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.

  3. 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.

  4. 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.

  5. 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 Pi 2 pyruvic acid + 2 NADH and 2 ATP

  6. Glycolysis • Glycolysis is exergonic. • Energy released used to drive endergonic reaction: • ADP + Pi ATP • Glucose must be activated first before energy can be obtained. • ATP consumed at the beginning of glycolysis.

  7. Glycolysis • ATP ADP + Pi • Pi 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.

  8. 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.

  9. 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

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

  11. Glycogenesis: formation of glycogen from glucose. • Glycogenolysis: conversion of glycogen to glucose-6-phosphate. • Glucose-6-phosphate can be utilized through glycolysis.

  12. 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.

  13. 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.

  14. 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.

  15. Aerobic Respiration • Pyruvic acid enters interior of mitochondria. • Converted to acetyl CoA and 2 C02. • Acetyl CoA serves as substrate for mitochondrial enzymes.

  16. Acetyl CoA enters the Krebs Cycle.

  17. 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 FADH2 • NADH and FADH2 transport electrons to Electron Transport Cycle.

  18. 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.

  19. ETC Chain • Each cytochrome transfers electron pairs from NADH and FADH2 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.

  20. ETC Chain • Cytochrome a3 transfers electrons to O2 (final electron acceptor). • Oxidative phosphorylation occurs: • Energy derived is used to phosphorylate ADP to ATP.

  21. 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.

  22. 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+.

  23. 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 Pi ATP

  24. Coupling ETC to ATP • Oxygen functions as the last electron acceptor. • Oxidizes cytochrome a3. • Oxygen accepts 2 electrons. • O2 + 4 e- + 4 H+ 2 H20

  25. 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 FADH2 donates ((activates 2nd and 3rd proton pumps). • 26 ATP produced.

  26. Metabolism of Lipids • When more energy is taken in than consumed, glycolysis inhibited. • Glucose converted into glycogen and fat.

  27. Lipogenesis • Formation of fat. • Occurs mainly in adipose tissue and liver. • Acetic acid subunits from acetyl CoA converted into various lipids.

  28. Metabolism of Lipids • Lipolysis: • Breakdown of fat. • Triglycerides glycerol + fa • Free fatty acids (fa) serve as blood-borne energy carriers. lipase

  29. Beta-oxidation • Enzymes remove 2-carbon acetic acid molecules from acid end of fa. • Forms acetyl CoA. • Acetyl CoA enters Krebs Cycle.

  30. 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.

  31. Adequate amino acids are required for growth and repair. A new amino acid can be obtained by: • Transamination: • Amino group (NH2) transferred from one amino acid to form another.

  32. Process by which excess amino acids are eliminated. • Amine group from glutamic acid removed, forming ammonia and excreted as urea.

  33. Deamination • Energy conversion: amino acid is deaminated. • Ketoacid can enter the Krebs Cycle.

  34. Use of different energy sources.

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