Biochemistry Chapter on Cellular Respiration

Microbial Metabolism

• Microbial metabolism involves a series of enzymatically catalyzed chemical reactions.
• These reactions extract energy from organic compounds and store it in chemical form (ATP).

Oxidation-Reduction Reactions

• Oxidation: Removal of electrons.
• Reduction: Gain of electrons.
• Redox reaction: An oxidation reaction paired with a reduction reaction.
• In biological systems, electrons and protons are removed simultaneously, equivalent to a hydrogen atom.
• Biological oxidations are often dehydrogenations.

Carbohydrate Catabolism

• Breakdown of carbohydrates to release energy.
  • Glycolysis
  • Krebs cycle
  • Electron transport chain (system)

Glycolysis

• Oxidation of glucose to pyruvic acid produces ATP and NADH.

Cellular Respiration

• Oxidation of molecules liberates electrons to operate an electron transport chain.
• The final electron acceptor is inorganic and from outside the cell.
• ATP is generated by oxidative phosphorylation.

Aerobic Respiration

• Krebs cycle:
  • Pyruvic acid (from glycolysis) is oxidized and decarboxylation (loss of CO2) occurs.
  • The resulting two-carbon compound attaches to coenzyme A, forming acetyl CoA and NADH.
  • Oxidation of acetyl CoA produces NADH, FADH2, and ATP, and liberates CO2 as waste.

Carbohydrate Catabolism (Continued)

• Each NADH can be oxidized in the electron transport chain to produce 3 molecules of ATP.
• Each FADH2 can produce 2 molecules of ATP.

Anaerobic Respiration

• The final electron acceptor in the electron transport chain is not O2.
• Yields less energy than aerobic respiration.
  • Electron Acceptor: NO3-, SO42-, CO32-
  • Products: NO2, N2 + H2O; H2S + H2O; CH4 + H2O, respectively.

ATP Yield During Prokaryotic Aerobic Respiration

• Glycolysis: 2 ATP (substrate-level phosphorylation), 6 ATP (oxidative phosphorylation).
• Preparatory Step: 6 ATP (oxidative phosphorylation).
• Krebs Cycle: 2 GTP (equivalent of ATP; substrate-level phosphorylation), 18 ATP (oxidative phosphorylation), 4 ATP (oxidative phosphorylation).
• Total: 38 ATP

Fermentation

• Releases energy from the oxidation of organic molecules.
• Does not require oxygen.
• Does not use the Krebs cycle or ETC.
• Uses an organic molecule as the final electron acceptor.
• Produces only small amounts of ATP.

Types of Fermentation

• Lactic acid fermentation: Produces lactic acid.
  • Homolactic: Produces lactic acid only.
  • Heterolactic: Produces lactic acid and other compounds.
• Alcohol fermentation: Produces ethanol + CO2. Glucose is oxidized to pyruvic acid; pyruvic acid is converted to acetaldehyde and CO2; NADH reduces acetaldehyde to ethanol.

Lipid and Protein Catabolism

• Protein: Extracellular proteases → Amino acids → Deamination, decarboxylation, dehydrogenation, desulfurization → Organic acid → Krebs cycle.
• Lipid: Lipids (fats) → Lipase → Glycerol → Dihydroxyacetone phosphate, Glyceraldehyde 3-phosphate → Glycolysis → Pyruvic acid → Acetyl CoA → Krebs cycle.

Photosynthesis

• Light-dependent (light) reactions: Conversion of light energy into chemical energy (ATP and NADPH).
• Light-independent (dark) reactions: ATP and NADPH are used to reduce CO2 to sugar (carbon fixation) via the Calvin-Benson cycle.

Types of Photosynthesis

• Oxygenic: 6 CO2 + 12 H2O + Light energy → C6H12O6 + 6 H2O + 6 O2
• Anoxygenic: 6 CO2 + 12 H2S + Light energy → C6H12O6 + 6 H2O + 12 S

Photophosphorylation

• Two types: cyclic, non-cyclic.

Metabolic Diversity Among Organisms

• Phototrophs use light energy.
• Chlorophyll is oxidized.
• Photoautotrophs: Use energy in the Calvin-Benson cycle to fix CO2 to sugar.
  • Oxygenic: Produces O2.
  • Anoxygenic: Does not produce O2.
• Chemoautotrophs: Use inorganic compounds for energy.
• Chemoheterotrophs: Use organic compounds.

Biochemical Tests and Bacterial Identification

• Fermentation test: Detects bacteria capable of carbohydrate or protein catabolism, indicated by pH indicator color change.
• Oxidase test: Identifies bacteria with cytochrome oxidase using specific color reagent.

Test your knowledge on cellular respiration and fermentation processes in biochemistry. This quiz includes questions on electron transport chains, fermentation types, and the role of specific microorganisms. Perfect for students studying cellular metabolism.