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Chapter 4

Chapter 4. Cellular Metabolism. About this Chapter. Energy for synthesis and movement Energy transformation Enzymes and how they speed reactions Metabolic pathways ATP its formation and uses in metabolism Synthesis of biologically important molecules. Energy (E) Transfer Overview.

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Chapter 4

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  1. Chapter 4 Cellular Metabolism

  2. About this Chapter • Energy for synthesis and movement • Energy transformation • Enzymes and how they speed reactions • Metabolic pathways • ATP its formation and uses in metabolism • Synthesis of biologically important molecules

  3. Energy (E) Transfer Overview • Energy does work • Kinetic energy • Potential energy • Energy conversion

  4. Energy (E) Transfer Overview Figure 4-1: Energy transfer in the environment

  5. Chemosynthesis versus Photosynthesis Chemosynthesis • 6CO2 + 6H2S → C6H12O6 + 6S Needs heat added such as from hydrothermal vents in the deep ocean Photosynthesis • 2n CO2 + 2n H2O + photons → 2(CH2O)n + 2n O2 Occurs in Two Stages Stage 1: Light energy used to form ATP and NADPH Stage 2: Uses ATP and NADPH to reduce CO2

  6. Energy and Chemical Reactions Figure 4-5: Energy transfer and storage in biological reactions

  7. Formation of ATP from Carbs, Proteins and Fat • Enzymes of metabolic pathways are able to capture the energy contained in carbohydrates, proteins and fatty acids in small portions and store it in form of internal high energy compounds such as ATP, drastically reducing the amount of energy lost as heat.

  8. Adenosine Triphosphate (ATP) • Source of immediately usable energy for the cell • Adenine-containing RNA nucleotide with three phosphate groups

  9. Adenosine Triphosphate (ATP) Figure 2.22

  10. How ATP Drives Cellular Work Figure 2.23

  11. Protein • Macromolecules composed of combinations of 20 types of amino acids bound together with peptide bonds Figure 2.16

  12. Structural Levels of Proteins • Primary – amino acid sequence • Secondary – alpha helices or beta pleated sheets

  13. Structural Levels of Proteins Figure 2.17a-c

  14. Structural Levels of Proteins • Tertiary – superimposed folding of secondary structures • Quaternary – polypeptide chains linked together in a specific manner

  15. Structural Levels of Proteins Figure 2.17d, e

  16. 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

  17. Protein Synthesis Figure 4-34: Summary of transcription and translation

  18. Post – Translational protein modificaiton Figure 4-35: Post-translational modification and the secretory pathway

  19. Post – Translational protein modificaiton • Folding, cleavage, additions: glyco- lipo- proteins

  20. Characteristics of Enzymes • Most are globular proteins that act as biological catalysts • Holoenzymes consist of an apoenzyme (protein) and a cofactor (usually an ion) • Enzymes are chemically specific • Frequently named for the type of reaction they catalyze • Enzyme names usually end in -ase • Lower activation energy

  21. Characteristics of Enzymes Figure 2.19

  22. Enzymes speed biochemical reactions Figure 4-8: Two models of enzyme binding sites

  23. Mechanism of Enzyme Action • Enzyme binds with substrate • Product is formed at a lower activation energy • Product is released

  24. Enzymes speed biochemical reactions • Lower activation E • Specific • May require Cofactors or Coenzymes • Modulators • Acidity • Temperature • Competitive inhibitors • Allosteric • Concentrations

  25. Cofactors and Enzyme Activity • Cofactors are inorganic substrates. Some cofactors are required to produce a chemical reaction between the enzyme and the substrate, while others merely increase the rate of catalysis. Cofactors are sometimes attach to the enzyme, much like a prosthetic limb. Others are loosely bound to the enzyme.

  26. Coenzymes and Enzyme Activity • Unlike the inorganic cofactors, coenzymes are organic molecules. Certain enzymes need coenzymes to bind to the substrate and cause a reaction. Since the coenzymes are changed by the chemical reaction, these are considered to be secondary substrates of the reaction. Though enzymes are specific to the substrate, coenzymes are not specific to the enzymes they assist. Some chemical reactions within the cells of the body do require a cofactor or a coenzyme to work properly, while others do not. The body is unable to manufacture these products, so the way to get the vitamins necessary to produce cofactors and coenzymes is to eat a healthy, balanced diet full of all the vitamins necessary for bodily functions.

  27. Protein Denaturation • Reversible unfolding of proteins due to drops in pH and/or increased temperature Figure 2.18a

  28. Protein Denaturation • Irreversibly denatured proteins cannot refold and are formed by extreme pH or temperature changes Figure 2.18b

  29. Law of Mass Action • Defined: • Equlibrium • Reversible Figure 4-17: Law of mass action

  30. Types of Enzymatic Reactions • Oxidation–reduction • Hydrolysis–dehydration • Addition–subtraction exchange • Ligation

  31. Cell Metabolism • Pathways • Intermediates • Catabolic - energy • Anabolic - synthesis Figure 4-18b: A group of metabolic pathways resembles a road map

  32. Control of Metabolic Pathways • Feedback inhibition Figure 4-19: Feedback inhibition

  33. ATP Production • Glycolysis • Pyruvate • Anaerobic respiration • Lactate production • 2 ATPs produced Figure 4-21: Overview of aerobic pathways for ATP Production

  34. Pyruvate Metabolism • Aerobic respiration • In mitochondria • Acetyl CoA and CO2 • Citric Acid Cycle or Kreb’s Cycle or TCA Cycle • Energy Produced from 1 Acetyl CoA • 1 ATP • 3 NADH • 1 FADH2 • Waste–2 CO2s

  35. Pyruvate Metabolism Figure 4-23: Pyruvate metabolism

  36. Electron Transport • High energy electrons • Energy transfer • ATP synthesized from ADP • H2O is a byproduct- In a typical individual this amounts to approximately 400 ml/day

  37. Electron Transport Figure 4-25: The electron transport system and ATP synthesis

  38. Biomolecules Catabolized to make ATP • Complex Carbohydrates • Glycogen catabolism • Liver storage • Muscle storage • Glucose produced Figure 4-26: Glycogen catabolism

  39. Protein Catabolism • Deaminated • Conversion • Glucose • Acetyl CoA

  40. Protein Catabolism Figure 4-27: Protein catabolism and deamination

  41. Lipid Catabolism • Higher energy content • Triglycerides to glycerol • Glycerol • Fatty acids • Ketone bodies - liver

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