Chapter 6 - Enzymes

Question 1

List enzyme catalyzed reactions. (6)

Answer 1

Oxidoreductases, Transferases, Hydrolases, Lyases, Isomerases, Ligases

Question 2

What is oxidoreductases? Give examples.

Answer 2

Oxidations and reductions.
Ex: Dehydrogenases and oxidases

Question 3

What is Transferases? Give an example.

Answer 3

Transfer moieties or functional groups
Ex: Transaminases, Kinases, Glucose

Question 4

What is Hydrolases? Give examples.

Answer 4

Hydrolytic cleavage of covalent bonds using water.
Ex: Proteases, lipases, hydrolases

Question 5

What is Lyases? Give examples.

Answer 5

Cleavage covalent bonds, generating double bonds or DLB
Ex: Decarboxylases and X-lyases

Question 6

What is Isomerase? Give examples.

Answer 6

Structural changes within the molecule.
Ex: Racemases and isomerases (e.g. , D-alanine —> L-alanine)

Question 7

What is Ligases? Give examples.

Answer 7

The joining of 2 molecules.
Ex: DNA ligases and glutamine synthetase

Question 8

What are the different inhibitors of enzymes?

Answer 8

Competitive, non-competitive, and uncompetitive inhibitors.

Question 9

Describe competitive inhibitors.

Answer 9

Inhibitors compete with substrate to bind at active site, increasing the apparent 𝐾m because more substrate is need to reach half of 𝑉max. 𝑉max stays the same.

Question 10

Describe competitive inhibitors in a Lineweaver-Burk plot.

Answer 10

Competitive inhibition increases the slope (since 𝐾m increases), and the x-intercept shifts to zero, but same y-intercept.

Question 11

Describe Non-competitive inhibitors.

Answer 11

They bind to a different site on the enzyme, not affecting substrate binding (no change in 𝐾m) but decreasing 𝑉max because enzyme activity is reduced regardless of substrate concentration.

Question 12

Describe non-competitive inhibitors in a Lineweaver-Burk plot.

Answer 12

The slope increases and the y-intercept moves up (b/c 𝑉max decreases), x-intercept remains unchanged.

Question 13

Describe uncompetitive inhibitors.

Answer 13

Only bind to the enzyme-substrate complex, lowering both 𝐾m and Vmax.

Question 14

Describe Uncompetitive inhibitors in a Lineweaver-Burk plot.

Answer 14

Parallel lines where both the slope and intercepts shift proportionally, indicating simultaneous decreases in 𝐾 𝑚 K m and 𝑉max.

Question 15

What are the assumptions or hypothesis for Michaelis-Menten
equation? (5)

Answer 15

One-substrate enzyme catalyzed reaction.
Steady-state kinetics, [ES] does not change with time.
Rate-limiting step is the breakdown of ES to E+P.
Enzyme concentration is much smaller than substrate
concentrations.
Enzyme is not allosteric.