Questions Test 2

Question 1

Km and K0.5 give what information?

Answer 1

• describes the turnover rate of an enzyme once a substrate molecules binds
• gives information about the affinity of a ligand or substrate for the protein in which it binds

Question 2

What is the “ping-pong” mechanism?

Answer 2

a substrate must bind and be released as product before the second substrate can bind to the enzyme

Question 3

It is more useful for biochemists to know the specific activity of an enzyme than the activity of the enzyme because:

Answer 3

specific activity is a measure of the purity of the enzyme preparation

Question 4

Reversible interactions are mediated by

Answer 4

ES, HB, VDW

Question 5

Enzymes DIFFER from other non-enzymatic catalysts in that they:

Answer 5

usually display specificity towards a single reactant

Question 6

4. Which of the following statements is TRUE about enzyme catalysts?

Answer 6

C) They lower the activation energy for the conversion of substrate to product, thus enzymes increase the rate at which substrate is converted into product.

Question 7

7. The enzyme carbonic anhydrase requires Zn2+ to catalyze formation of carbonic acid from H2O and CO2. Under conditions of zinc deficiency, when the enzyme lacks zinc, the enzyme would be referred to as the carbonic anhydrase:

Answer 7

A) apoenzyme

Question 8

10. Which of the following statements is FALSE about a plot of Vo versus [S] for an enzyme that follows Michaelis-Menten kinetics?

Answer 8

D) KM is the initial velocity at which [S] = 1/2 Vmax

Question 9

Which amino acids in chymotrypsin are found in the active site and are participants in substrate cleavage?

Answer 9

asp, his, ser

Question 10

What is the ratio [S] to Km when the velocity of the reaction 80% Vmax?

Answer 10

4

Question 11

For an enzyme that follows simple Michaelis-Menten kinetics, what is the value of Vmax if V0 is equal to 1 umol/min at 1/10 Km?

Answer 11

11 umol/min

Question 12

The Km is

Answer 12

equal to the substrate concentration when the reaction rate is half maximal

Question 13

(T/F) The substrate and allosteric effectors of ATCase in E.coli bind at different sites.

Answer 13

False

Question 14

(T/F) Concerning a concerted mechanism of allosteric regulation, all of the subunits are in either the T or the R state.

Answer 14

True

Question 15

The isozymes of human Lactate Dehydrogenase

Answer 15

function optimally under different oxygen conditions

Question 16

Which chain is considered the active chain of chymotrypsin?

Answer 16

149-245

C chain

Question 17

What must occur for chymotypsin to be active?

Answer 17

a salt bridge between N-term Ile16 (B) and Asp194 in C-chain