Biology: Chap. 5/6

Enzyme Functioning and Proteases

• Enzymes: Biological catalysts that speed up chemical reactions in cells by lowering the activation energy required for reactions.
• Protease: A specific type of enzyme that catalyzes the hydrolysis of proteins, breaking them down into amino acids.
  • Example: Hydrolysis of soy protein for flavor enhancement in food products (e.g., hydrolyzed soy protein).

Enzyme Action and Hydrolysis

• Proteins, when hydrolyzed, release individual amino acids, which often have stronger flavors compared to whole protein structures.
• Chemical Process of Hydrolysis:
  • Involves breaking peptide bonds using acids (e.g., hydrochloric acid) and heat to facilitate the reaction:
    \text{Protein} + \text{H}^+ \rightarrow \text{Amino Acids}

Importance of Molecular Motion

• Molecules in a solution (e.g., water) move randomly. To facilitate specific reactions, enzymes reduce randomness by providing a fixed environment (active site) where specific substrates can bind.
• Active Site: An area within the enzyme that is shaped specifically to bind to its substrate, facilitating the reaction without randomness in molecular motion.

Mechanism of Enzyme-Substrate Interaction

• Specificity:
  • Enzymes have an active site that matches a specific substrate based on shape.
  • Upon binding, the enzyme catalyzes a reaction that reduces the energy needed for the reaction to occur. This specificity eliminates random molecular interactions.

Regulation of Enzyme Activity

• Enzyme Inhibition: Cells can regulate enzyme activity by using inhibitors that affect enzyme function.
  • Competitive Inhibition: Inhibitor resembles the substrate and competes for the active site, preventing the substrate from binding.
  • Non-Competitive (Allosteric) Inhibition: Inhibitor binds to a site other than the active site (allosteric site), causing a change in enzyme shape and reducing its activity.

Real-World Examples of Enzyme Inhibition

• Medications like ibuprofen inhibit enzymes such as prostaglandin synthase to reduce inflammation and pain by blocking active sites.

Feedback Inhibition Mechanism

• A common regulatory mechanism where the end product of a reaction pathway inhibits an enzyme involved earlier in the pathway, preventing overproduction of that product.
• Example: If sufficient chemical D is produced in a metabolic pathway, it can inhibit the enzyme that catalyzes its own production, regulating the entire pathway.

Overview of Cellular Respiration

• Aerobic Respiration: Involves oxidation of glucose with oxygen to produce ATP, carbon dioxide, and water.
• Stages of Respiration:
  1. Glycolysis - Occurs in cytoplasm, splits glucose into pyruvate (net 2 ATP, 2 NADH).
  2. Pyruvate Oxidation - Converts pyruvate into acetate (produces NADH and CO2).
  3. Citric Acid Cycle (Krebs Cycle) - Fully oxidizes acetate to CO2 (produces ATP, NADH, FADH2).
  4. Oxidative Phosphorylation - Generates ATP using reducing power from NADH and FADH2 in the electron transport chain.

Glycolysis Details

• Stages:
  • Energy Investment Phase (requires ATP to split glucose).
  • Energy Payoff Phase (produces ATP and NADH from the oxidation of glyceraldehyde-3-phosphate to pyruvate).
• Net Gain: Overall, glycolysis yields 2 ATP and 2 NADH per glucose molecule.

Pyruvate Oxidation and Citric Acid Cycle

• Pyruvate Oxidation: Converts pyruvate to acetyl CoA, producing NADH and CO2.
• Citric Acid Cycle:
  • Takes place in mitochondrial matrix; completes glucose oxidation, producing ATP, NADH, and FADH2 while releasing CO2.
  • Each turn of the cycle yields 3 NADH, 1 FADH2, and 1 ATP.

Overall Metabolic Summary

• The energy from glucose is first converted into ATP, but the majority of the energy is stored in the reducing agents (NADH, FADH2). These coenzymes are crucial in transferring electrons for ATP production during oxidative phosphorylation.
• Significance of Coenzymes: Coenzymes facilitate enzymatic reactions and cannot be synthesized by the body alone; thus they must be obtained through the diet.

Key Terms

• NAD/NADH: Important electron carriers in cellular respiration. NAD is oxidized; NADH is reduced.
• FAD/FADH2: Similar to NAD, FAD is another carrier protein involved in oxidation-reduction reactions during cellular respiration.