export_enzymes

Question 1

MM equation assumptions

Answer 1

1. Single enzyme
2. Single product
3. Steady state
4. Formation of product is rate limiting

Question 2

The initial rate of an enzymatic reaction is usually measured by determining the changing concentration of

Answer 2

Product

Question 3

Characteristic that defines rate of a spontaneous reaction

Answer 3

Difference in energy between the reactant(s) and the transition state

Question 4

Defines the position of a spont. reaction at equilibrium

Answer 4

Difference in energy between the product(s) and the reactant(s)

Question 5

An enzyme that is able to act as a general base catalyst of an enzyme-catalyzed reaction

Answer 5

Glutamate

Question 6

Units for Km

Answer 6

μM

Question 7

Units for Kcat/KM

Answer 7

μM*s-1

Question 8

Uncompetitive inhibitors

Answer 8

• Only bind to ES complex

* Uncompetitive inhibitor binds at a site that is different from active site

Question 9

Describe mixed mode inhibition

Answer 9

• Apparent Km increase, and Vmax decrease

* Equal affinity to bind with E or ES complex

Question 10

What happens to Kcat/Km in competitive enzyme inhibition

Answer 10

Decrease

Question 11

What is the best kinetic parameter to compare one enzyme’s utilization of two different substrates?

Answer 11

Kcat/Km

Question 12

Enzymes increase the rate of reaction by

Answer 12

Dictating the geometry of reactions

Question 13

When comparing a catalyzed and an uncatalyzed reaction, what changes

Answer 13

• ΔG

* Initial rate of rxn

Question 14

How do competitive, uncompetitive, and mixed mode inhibitors differ in their mode of action?

Answer 14

• Competitive : binds to enzyme at active site
• uncompetitive : binds to enzyme-substrate complex at other site
• mixed : bonds to enzyme or enzyme-substrate complex at other site

Question 15

Chymotrypsin belongs to a group of proteolytic enzymes called the “serine proteases,” many of which have an Asp, His, and Ser residue that are crucial to the catalytic mechanism. The serine hydroxyl functions as a nucleophile. What do the other two amino acids do to support this nucleophilic reaction?

Answer 15

• histidine functions as a general base, accepting a proton from the serine hydroxyl, thereby increasing serine’s reactivity as a nucleophile.
• The negatively charged Asp stabilizes the positive charge that develops on the His.

Question 16

Chymotrypsin cleaves on the C-side of amino acid residues with flat, nonpolar side chains. Trypsin cleaves on the C-side of arginine and lysine, while elastase cleaves on the C-side of glycine and alanine. What amino acids in the structure of the enzymes account for these differences?

Answer 16

Chymotrypsin has a deep hydrophobic pocket. The binding pocket in trypsin has an aspartate at the bottom, while elastase has bulky valine and threonine causing a shallow pocket.

Question 17

What kind of covalent intermediate is involved in the aldolase mechanism? What amino acid side chain is involved?

Answer 17

Imine (Schiff base) formed with lysine

Question 18

What metal ions are involved in the enolase mechanism and what role do they play?

Answer 18

Mg2+. Stabilize the enolate thus making the C-H more acidic.

Question 19

What is the standard way to compare enzyme efficiencies?

Answer 19

specificity constant – kcat/Km

Question 20

Carboxypeptidase A will not remove the C-terminal amino acid if it is Lysine or Arginine, while carboxypeptidase B will only remove terminal Lys or Arg. What amino acid would you expect to be present in the binding pocket of carboxypeptidase B?

Answer 20

Aspartate or glutamate

Question 21

Competitive, uncompetitive, and mixed mode inhibitors are all types of reversible inhibitor. What do irreversible inhibitors do?

Answer 21

Bind covalently with or destroy a functional group that is essential for the enzyme’s activity.

Question 22

Kcat/Km is a measure of

Answer 22

an enzymes catalytic efficiency, also called the specificity constant – best way to compare two different enzymes or two different substrates for the same enzyme

Question 23

Kcat is a general rate constant, also called the

Answer 23

turnover number , that describes the limiting rate in any enzyme catalyzed reaction at saturation