Biochemistry Chapter 8 Section 4

Enzymes and Their Functions

• Enzymes are proteins that act as catalysts to increase the rates of chemical reactions.
• They lower the activation energy necessary for reactions, enabling them to proceed more quickly.
• Enzymes do not alter the free energy change of a reaction; they only influence reaction speed.

Activation Energy

• Activation energy (Ea or ΔG✳) is the minimum energy required to initiate a chemical reaction.
• Example: In cellular respiration, 2 ATP are needed to convert glucose into pyruvic acid.

Active Site and Substrate Specificity

• The active site is the part of the enzyme where the catalytic reaction occurs and is specifically shaped to fit its substrates.
• Enzyme-substrate specificity emphasizes that only certain substrates can bind to an enzyme's active site, reminiscent of a "lock and key" model.

Induced Fit Model

• This model suggests that initial interactions between an enzyme and substrate are weak, but these weak bonds induce conformational changes that enhance binding strength.

Factors Affecting Enzyme Activity

• Optimal conditions for enzyme activity include a pH of 6-8 and a temperature range of 30-40 °C.
• Enzyme activity can be influenced by the presence of cofactors, inhibitors, and denaturing conditions.

Cofactors and Coenzymes

• Cofactors are non-protein molecules that assist enzymes in catalysis, which can be permanently or reversibly bound.
• Coenzymes are specific types of organic cofactors, commonly derived from vitamins.

Inhibition Mechanisms

• Competitive inhibitors resemble substrates and compete for the enzyme's active site.
• Noncompetitive inhibitors bind elsewhere on the enzyme, changing its shape and hindering substrate binding or function.

Enzyme Regulation

• Allosteric regulation describes how binding of a molecule affects protein function at a different site, potentially acting as either an inhibitor or activator.
• Cells regulate enzyme activity through various methods including allosteric control, feedback inhibition, and enzyme synthesis regulation at the gene level.

Cooperativity

• Cooperativity occurs when substrate binding to one active site influences the binding of another substrate.
• Positive cooperativity enhances the affinity for subsequent substrate binding, while negative cooperativity decreases it.

Feedback Inhibition

• This cellular control mechanism inhibits an enzyme when its product accumulates to a certain level, maintaining balance within the metabolic pathway.
• Example: Dysregulation of feedback inhibition for insulin can lead to diabetes.

Conclusion

• By regulating enzyme activity effectively, cells can maintain control over metabolic processes, ensuring proper levels of reactants and products.