chapter 13 section 6

Question 1

What is the lock-and-key hypothesis?

Answer 1

Emil Fischer proposed that enzymes are like locks and substrates like keys, explaining the specificity of enzyme-substrate interactions.

Question 2

Are enzymes rigid like locks?

Answer 2

No; enzymes are not rigid templates—they can undergo conformational changes.

Question 3

What is the induced-fit hypothesis?

Answer 3

roposed by Daniel Koshland, it states that substrate binding causes a conformational change in the enzyme, improving the fit between enzyme and substrate.

Question 4

How does induced fit affect the substrate?

Answer 4

The substrate also changes shape to better match the enzyme, making recognition a dynamic, interactive process.

Question 5

What two factors ultimately determine substrate specificity in the induced-fit model?

Answer 5

1) Weak binding of the substrate to the enzyme, and (2) the rate of the substrate-induced conformational change

Question 6

How does induced fit explain the high catalytic power of enzymes?

Answer 6

Substrate binding positions catalytic residues precisely via conformational changes, enabling efficient catalysis.

Question 7

How does the induced-fit model relate to the transition state?

Answer 7

The enzyme-substrate complex induces the substrate to adopt a shape resembling the transition state, favoring catalysis

Question 8

What defines a poor substrate in the context of induced fit?

Answer 8

A poor substrate is one that fails to effectively induce the enzyme into the catalytically active, transition-state–mimicking conformation.

Question 9

What happens to the enzyme in the absence of substrate?

Answer 9

The enzyme reverts to a more stable, different conformation since the active, transition-state–favoring structure is relatively unstable without substrate.

Question 10

Why does hexokinase phosphorylate hexoses but not smaller molecules like glycerol or water?

Answer 10

Smaller molecules do not induce the conformational change needed for hexokinase to reach its fully active catalytic state.

Question 11

How does substrate binding activate hexokinase?

Answer 11

Binding induces a conformational change that brings the two protein domains together

Question 12

Could water act as a phosphoryl acceptor for hexokinase? Why or why not?

Answer 12

No, even though water can access the active site, it does not trigger the conformational change required for catalysis.

Question 13

Where is the hexose-binding site located in hexokinase?

Answer 13

Between two protein domains; substrate binding causes these domains to close, forming the active site.