Ch. 5 Enzyme Structure and Function Quiz

Enzyme Structure and Function

• Apoenzyme: The protein portion of an enzyme.
• Cofactor: Non-protein component necessary for enzyme activity, often ions like Mg²⁺ or Ca²⁺.
• Holoenzyme: Combination of an apoenzyme and its cofactor, representing the functional form.
• Inhibitors: Substances that reduce enzyme activity, can be competitive or non-competitive.

Factors Influencing Enzyme Activity

• Temperature: High temperatures increase activity until denaturation occurs; low temperatures slow down the reaction.
• pH: Extreme pH levels can denature enzymes, significantly affecting activity.
• Substrate Concentration: High substrate concentration leads to maximum enzyme catalysis, termed saturation.

Types of Inhibitors

• Competitive Inhibitors: Compete with substrate for the active site, preventing formation of the enzyme-substrate complex.
• Non-Competitive Inhibitors: Bind to allosteric sites on the enzyme, changing its activity without competing at the active site.

Metabolism Overview

• Metabolism includes catabolism (breaking down molecules) and anabolism (building molecules).
• Involves enzymes, redox reactions (oxidation-reduction), and the production of energy carriers: ATP, NADH, and FADH₂.
• Crucial processes include aerobic respiration and fermentation.

Oxidation-Reduction Reactions

• Oxidation: Loss of electrons that releases energy.
• Reduction: Gain of electrons.
• Redox Reaction: Pairing of oxidation and reduction processes essential in metabolic pathways.

ATP: The Energy Currency

• ATP (Adenosine Triphosphate): Acts as an energy shuttle; energy is released when the terminal phosphate bond is broken.
• ATP Hydrolysis Reaction: ATP + H₂O → ADP + Pi + energy.
• Structure includes ribose, adenine, and three phosphate groups.
• ATP drives endergonic reactions through the transfer of phosphate groups.

Phosphorylation of ADP

• Converts ADP to ATP using energy input through:
  • Substrate-level phosphorylation: Direct enzymatic transfer of a phosphate group.
  • Oxidative phosphorylation: Energy from the electron transport chain.
  • Photophosphorylation: Light energy incorporated into ATP.

Hydrogen Transport Molecules

• NAD⁺ / NADH: NADH is the reduced form, generated by adding hydrogen to NAD⁺.
• FAD / FADH₂: Similar role as NADH, functioning as electron carriers in metabolic reactions.
• Both are essential for transporting electrons during respiration.

Aerobic Respiration Stages

• Glycolysis: Breakdown of glucose into 2 pyruvate, yielding 2 ATP and 2 NADH; occurs in cytoplasm.
• Preparatory Reaction (Pyruvate Oxidation): Converts pyruvate into acetyl-CoA, producing 2 NADH.
• Citric Acid Cycle (Krebs Cycle): Breaks down acetyl-CoA, generating 2 ATP, 6 NADH, and 2 FADH₂; cyclical process.
• Electron Transport Chain (ETC): Utilizes NADH and FADH₂ to create a proton gradient, leading to ATP production (32 ATP per glucose molecule).

Mitochondrial Function

• Oxygen acts as the final electron acceptor in the ETC, producing water and maintaining the gradient for ATP synthesis.
• ATP Synthase: Enzyme that harnesses the proton gradient to synthesize ATP through phosphorylation.

Overall Yield of Aerobic Respiration

• Total ATP generated from one glucose molecule is approximately 36 to 38 ATP, depending on transport efficiency across mitochondrial membranes.
• Intermediate metabolites from carbohydrates, lipids, and proteins can enter aerobic respiration at various stages.