Exam 2 Lecture 13 Enzyme Kinetics

Question 1

A linear kinetic trend describes:

Answer 1

“Wishful thinking” as v = k[S]

Question 2

A hyperbolic kinetic trend describes:

Answer 2

Michaelis-Menton Model

Question 3

A sigmoidal kinetic trend describes:

Answer 3

Cooperative binding

Question 4

Was is the equation for irreversible rxn and what does it allude to?

Answer 4

v = k[S]^n

Alludes to reaction rate as n indicates reaction order ie how many things have to come together to make product

Question 5

1S—>P describes:

Answer 5

First order kinetics: v = k[S]^1

Question 6

2S—>P or Sa + Sb —> P describes:

Answer 6

2nd order kinetics: v = k[S]^2 or k[Sa][Sb]

Question 7

S—>P describes:

Answer 7

Zero order kinetics: v = k[S]^0 = k
Is a unimolecular rxn because an internal change. No breaking of bonds or do not an enzyme (uncatatalyzed) or enzyme is saturated ie all active sites are full

(Irreversible rxn)

Question 8

S —>k1—>P; and the reverse from P to S (k-1)

Answer 8

REVERSIBLE rxn

Substrate is being both used and created

v = k1[S]^n - k-1[P]^m

Question 9

At EQUILIBRIUM by definition, the forward rate equals

Answer 9

The reverse rate

v= k1[S] - k-1[P] = 0

k1[S] = k-1[P]

Question 10

For a reversible rxn at equilibrium, we now can redefine our 2 equilibrium constants which are:

Answer 10

K(A) = association constant; making product k1/k-1

K(D) = dissociation constant; unmake product 1/K(A)

Question 11

T/F: catalysis is not a 1st order rxn?

Answer 11

True

Question 12

MM enzymes follow _ order kinetics

Answer 12

1st order kinetics

Question 13

Km

Name and definition

Answer 13

Michaelis Constant
[S] where rxn rate is half maximal or half of the active sites are full
Related to the affinity of the enzyme for the substrate

Question 14

Vmax

Name and definition

Answer 14

Maximum velocity

Maximum rate possible for a given concentration of enzyme

Question 15

Kcat

Name and definition

Answer 15

Turnover number
How fast ES complex proceed to E + P
Number of substrate molecules converted per active site per time (first order rate constant sec-1)

Question 16

Ks

Name and definition

Answer 16

N/A

A dissociation constant for substrate binding

Question 17

Kcat/Km

Name and definition

Answer 17

Specificity constant

Measure of enzyme performance by predicting the fate of E*S (ability to convert substrate to product)

Question 18

Laboratory condition:

[S] is much less than Km:

Answer 18

At very low substrate concentration :
Vo = (Vmax/Km)*[S]; that is, the reaction is first order with the rate directly proportional to the substrate concentration.

Question 19

Laboratory condition:

[S] is much greater than Km:

Answer 19

At high substrate concentration, when [S] is much greater than Km, Vo = Vmax;

that is, the rate is maximal. The reaction is zero order, independent of substrate concentration.

Question 20

Laboratory condition:

[S] = Km

Answer 20

When [S] = Km, then Vo = Vmax/2

Thus, Km is equal to the substrate concentration at which the reaction rate is half its maximal value.

Question 21

What is the specificity constant?

Answer 21

(Kcat/Km)

Question 22

A good enzyme would have:

Answer 22

Kcat much greater than k-1 and
Kcat/Km = k1

good enzyme will take enzyme substrate complex and go to product

Question 23

A poor enzyme would have?

Answer 23

Kcat much less than k-1 and
Kcat/Km = 1/Km

bad enzyme we are falling apart and going back to substrate

Question 24

Multiple binding site enzymes CAN follow Michaelis-Menten kinetics as long as they are __

Answer 24

NONCOOPERATIVE

• cooperative enzyme = sigmoidal shape bc active sites are not equivalent; they’re not independent
• If each active site is independent of its neighbor, we get hyperbolic curve we expect of MM enzyme (kinetics) noncooperative

Question 25

Inhibitors can be either:

Answer 25

Irreversible (tightly bound to the enzyme) or reversible (rapid dissociation of the enzyme-inhibitor comples)

Question 26

Reversible inhibitors use what type of interaction to bind?

Answer 26

Noncovalent interactions

Question 27

Reversible inhibitors result in one of the following types of inhibition:

1. Competitive
2. Noncompetitive
3. Uncompetitive

Which are allosteric inhibitors?

Answer 27

Noncompetitive and uncompetitive

Question 28

Competitive inhibition:

Vmax is _
Km is _

Answer 28

Vmax is CONSTANT
Km is VARIABLE

no effect on Vmax but increase Km. Diminishes the rate of catalysis by reducing the proportion of enzyme molecules bound to substrate; takes longer to get to Vmax

Question 29

Noncompetitive inhibition:

Vmax is _
Km is _

Answer 29

Vmax is VARIABLE
Km is CONSTANT

Km is unaltered and Vmax is decreased. Inhibitor and substrate can bind simultaneously to an enzyme at different binding sites; inhibitor lowers the conc of functional enzyme as it can bind to free enzyme or the enzyme-substrate complex

Question 30

Uncompetitive inhibition:

Vmax is _
Km is _

Answer 30

Vmax is VARIABLE
Km is VARIABLE

Vmax and Km are reduced by equivalent amounts. Inhibitor binds only to the enzyme-substrate complex. The enzyme-substrate-inhibitor complex does not form any product

Question 31

Irreversible inhibitors _ enzymes

Answer 31

Inactivate enzymes

Question 32

Group-specific irreversible enzyme:

What it does:

Answer 32

Target a specific amino acid

Question 33

Group-specific irreversible enzyme:

Specificity for active site:

Answer 33

Low

Question 34

Group-specific irreversible enzyme:

Textbook example:

Answer 34

DIPF targets Serines

Question 35

Substrate Analogs irreversible enzyme:

What it does?

Answer 35

Substrate mimic, modifies enzyme

Question 36

Substrate Analogs irreversible enzyme:

Specificity for active site?

Answer 36

High

Question 37

Substrate Analogs irreversible enzyme:

Textbook example?

Answer 37

TPCK looks like Phe to chymotrypsin

Question 38

Suicide inhibitors irreversible inhibitor:

What it does?

Answer 38

Modified a substrate so is unable to form products

Question 39

Suicide inhibitors irreversible inhibitor:

Specificity for active site?

Answer 39

Very high

Question 40

Suicide inhibitors irreversible inhibitor:

Textbook example?

Answer 40

N,N-Dimethylpropargylamine inactivates FAD

Question 41

Km that is low (small number)

Answer 41

Reaches Vmax at a lower [S]; tight binding

Question 42

Km that is high (large number)

Answer 42

Reaches Vmax at a higher [S]; lower affinity ie higher [S] required to reach 1/2 Vmax

Question 43

Km=

Answer 43

(k-1 +k2)/k1