ch 5 exam review

Enzyme Components and Their Mechanisms of Action

Enzymes are biological catalysts that speed up chemical reactions without being consumed. Their components include:

1. Apoenzyme – The protein portion, inactive without a cofactor.

2. Cofactor – A non-protein component that assists the enzyme (e.g., metal ions like Mg²⁺, Zn²⁺).

3. Coenzyme – An organic cofactor (e.g., vitamins like NAD⁺, FAD, CoA).

4. Holoenzyme – The fully active enzyme (apoenzyme + cofactor/coenzyme).

Mechanism of Action:

• Substrate Binding – The substrate binds to the enzyme's active site, forming the enzyme-substrate complex.

• Induced Fit – The enzyme slightly changes shape for better substrate fit.

• Catalysis – The enzyme facilitates the reaction by lowering activation energy.

• Product Release – The reaction products are released, and the enzyme is free to catalyze again.

Factors Influencing Enzyme Activity

1. Temperature – Enzyme activity increases with temperature but denatures at extreme heat.

2. pH – Each enzyme has an optimal pH; too acidic or basic conditions can denature it.

3. Substrate Concentration – Higher substrate levels increase activity until saturation.

4. Inhibitors:

   • Competitive Inhibition – Inhibitors bind the active site, blocking the substrate.

   • Non-Competitive Inhibition – Inhibitors bind an allosteric site, altering enzyme shape.

5. Cofactors & Coenzymes – Some enzymes require these for activity.

6. Glycolysis and Other Pathways

   Glycolysis:

   • Occurs in: Cytoplasm

   • Main Steps:

     1. Glucose (C₆H₁₂O₆) → 2 Pyruvate

     2. Uses 2 ATP, produces 4 ATP (net gain: 2 ATP)

     3. Produces 2 NADH

   Pentose Phosphate Pathway (PPP):

   • Generates NADPH and ribose-5-phosphate (for nucleotide synthesis).

   • Important in anabolic reactions (e.g., fatty acid synthesis).

7. Entner-Doudoroff Pathway (EDP):

   • Alternative glycolytic pathway in bacteria.

   • Produces 1 ATP, 1 NADH, and 1 NADPH per glucose.

   • This pathway is particularly significant in organisms that utilize it for energy production in anaerobic conditions, allowing them to thrive in environments where traditional glycolysis may be less efficient.

Krebs Cycle (Citric Acid Cycle) & Its Significance

• Location: Mitochondrial matrix (eukaryotes), cytoplasm (prokaryotes).

• Purpose: Completes glucose oxidation to CO₂, generating high-energy carriers.

• Outputs per Acetyl-CoA:

  • 3 NADH

  • 1 FADH₂

  • 1 ATP (via GTP)

  • 2 CO₂

Significance: Provides electrons for oxidative phosphorylation (ATP production).

Lipid and Protein Catabolism

• Lipids: Broken down by lipases into glycerol and fatty acids.

  • Glycerol enters glycolysis.

  • Fatty acids undergo β-oxidation → Acetyl-CoA → Krebs cycle.

• Proteins: Broken down by proteases into amino acids.

  • Amino acids undergo deamination → Krebs cycle intermediates.

  Aerobic vs. Anaerobic Respiration vs. Fermentation

  Feature	Aerobic Respiration	Anaerobic Respiration	Fermentation
  Final Electron Acceptor	O₂	Non-O₂ molecule (e.g., nitrate, sulfate)	Organic molecule
  ATP Yield	~36-38 ATP	2-36 ATP	2 ATP
  End Products	CO₂, H₂O	CO₂, reduced compounds	Lactic acid or ethanol

Nutritional Classifications of Organisms

Examples:

• Plants → Photoautotrophs

• Some bacteria → Chemoautotrophs

• Humans → Chemoheterotrophs