Table of contents

1. Introduction to Biochemistry4h 34m
2. Water3h 23m
3. Amino Acids8h 10m
4. Protein Structure10h 4m
5. Protein Techniques14h 5m
6. Enzymes and Enzyme Kinetics13h 38m
7. Enzyme Inhibition and Regulation 8h 42m
8. Protein Function 9h 41m
9. Carbohydrates7h 49m
10. Lipids5h 49m
11. Biological Membranes and Transport 6h 37m
12. Biosignaling9h 45m
Review 1: Nucleic Acids, Lipids, & Membranes2h 47m
Review 2: Biosignaling, Glycolysis, Gluconeogenesis, & PP-Pathway3h 12m
Review 3: Pyruvate & Fatty Acid Oxidation, Citric Acid Cycle, & Glycogen Metabolism2h 26m
Review 4: Amino Acid Oxidation, Oxidative Phosphorylation, & Photophosphorylation1h 48m

6. Enzymes and Enzyme Kinetics

Kcat

Biochemistry

6. Enzymes and Enzyme Kinetics

Kcat

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Multiple Choice

Studies with mutated forms of an enzyme show that changing some active-site amino acids decrease the enzyme's turnover number (k_cat) but do not affect the K _m of the reaction. What is the best interpretation of these results?

The K_m of the enzyme for the substrate does not depend on amino acid side chains found in the active site.

The two terms, K_m and turnover number, are inversely proportional.

The transition state for this reaction is formed prior to the formation of the ES complex.

Amino acids involved in stabilizing transition-state complexes can be different than those affecting the ES-complex.

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Verified step by step guidance

Begin by understanding the terms involved: kcat (turnover number) and Km (Michaelis constant). kcat represents the number of substrate molecules converted to product per enzyme molecule per unit time when the enzyme is saturated with substrate. Km is the substrate concentration at which the reaction velocity is half of the maximum velocity.

Consider the role of active-site amino acids in enzyme function. These amino acids can be involved in substrate binding, transition state stabilization, or catalysis. Changes in these amino acids can affect different aspects of enzyme activity.

Analyze the effect of mutations on kcat and Km. The decrease in kcat suggests that the mutations affect the catalytic efficiency of the enzyme, possibly by altering the transition state stabilization or the catalytic mechanism.

Note that Km remains unchanged, indicating that the substrate binding affinity is not affected by the mutations. This suggests that the amino acids altered by the mutations are not involved in substrate binding but rather in the catalytic process.

Conclude that the amino acids involved in stabilizing the transition-state complexes can be different from those affecting the enzyme-substrate (ES) complex formation. This explains why kcat is affected while Km remains constant.