"Molecular & Cellular Princ Med Enzymes as Biological Catalysts Patricia Kanepopp" GABY Flashcards Preview

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Flashcards in "Molecular & Cellular Princ Med Enzymes as Biological Catalysts Patricia Kanepopp" GABY Deck (37)
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1
Q

Why do we say that enzymes play a central role in biology?

A
  1. Carry out almost all chemistry required by living systems
  2. Permit a wide range of chemical reactions in a narrow set of conditions
  3. Allow rapid, efficient adjustments to environmental conditions
2
Q

Medical Aspects of Enzymology

A
  1. Diseases traceable to enzymatic defects
  2. Use of enzyme activities in diagnosis
  3. Drugs as enzyme inhibitors
  4. Therapeutic administration of enzymes
  5. Design of therapeutic enzymes and enzyme inhibitors
3
Q

General Characteristics of Enzymes

A
  1. Tremendous enhancement of reaction rate
  2. Reactions occur under relatively mild conditions
  3. Extreme specificity
  4. Capacity for regulation
4
Q

Why are enzyme kinetics important?

A

It serves as an important tool in understanding enzyme mechanism and manipulating enzyme function

5
Q

Before Vmax is achieved, the initial rate of an enzymatic reaction depends on ___

A

substrate concentration

6
Q

After Vmax is achieved, the initial rate of an enzymatic reaction does not depend on ___

A

substrate concentration

7
Q

What happens to the enzyme-substrate complex (ES) after it is formed?

A

It can either dissociate into E+S
OR
it can go on to form product
E+P

8
Q

Must an ES complex form for the reaction to take place?

A

YES

9
Q

At low substrate concentrations, ___ limits how much ES can form, so v is ___ on [S]

A

[S]; dependent

10
Q

At high substrate concentrations, ___ limits how much ES can form, so v is ___ of [S]

A

[E]; independent

11
Q

What do k1, k2 and k3 mean?

A

They are kinetic constants

k1 of the –> E+S=ES reaction

k2 of the –> ES=E+S reaction

k3 of the –> ES=E+P reaction

12
Q

Is it possible to determine the kinetic constants relative values?

A

Yes, by making some assumptions

13
Q

Michaelis-Menten equation

A

v=(Vmax)X[S]/([S] + Km)

Vmax = k3 [E]t 
Km = (k2 + k3)/k1
14
Q

Can Km and Vmax be determined experimentally?

A

You can estimate Km and Vmax from a v vs [S] plot, but they are more accurately determined from a linearized form of the Michaelis-Menten equation (Lineweaver-Burk plot)

15
Q

What does the Km mean?

A

Km = [S] at which v = 1/2 Vmax

16
Q

Km will always have units of ___

A

CONCENTRATION!

17
Q

The catalytic rate of an enzyme is MOST SENSITIVE to [S] when ___

A

[S] &laquo_space;Km

18
Q

Knowing the Km allows you to calculate what fraction of enzyme molecules are bound to substrate at any [S]

A

fES=(v/Vmax)= [S]/([S] + Km)

19
Q

When k2»k3, i.e. the substrate binds and dissociates many times before it goes onto form product…

A

Km is approximately the same as the dissociation constant (Kd) for the ES complex under these conditions

20
Q

Km is approximately equal to Kd when ___

A

k2»k3

*Km = k2/k1 = Kd for ES complex

21
Q

T or F: Enzymes with low vs. high Km are adapted to different physiological functions

A

True

Examples: hexokinase (low Km) & glucokinase (high Km)

22
Q

What does the Vmax mean?

A

Vmax = maximal velocity achievable for a specific concentration of enzyme

*Note: Vmax will have units of velocity

23
Q

What is kcat?

A

A constant that is independent of enzyme concentration

kcat = Vmax/ [E]t
*[E]t = total enzyme conc.
24
Q

What does kcat/Km allow?

A

Direct comparison of enzyme efficiencies

25
Q

Why does higher kcat/Km imply higher efficiency?

A

kcat–determines how quickly ES complex is used

Km–describes how much ES complex is available

26
Q

Why can we determine [E]t from reaction rate under Vmax conditions?

A

Because under Vmax conditions (enzyme saturated with substrate) v is directly proportional to the concentration of enzyme present

27
Q

Lineweaver-Burk plot equation

A

1/v = 1/Vmax + (Km/Vmax)(1/[S])

*slope=Km/Vmax

28
Q

Irreversible enzyme inhibitors

A

Bind very tightly to an enzyme and inactivate an essential functional group on the enzyme

29
Q

Reversible enzyme inhibitors

A

Bind reversibly to enzyme and give temporary inactivation while they are bound

30
Q

What types of reversible enzyme inhibitors are there?

A
  1. Competitive
  2. Non-competitive
  3. Uncompetitive
31
Q

Competitive Inhibitors

A
  • compete with substrate for binding to active site
  • inhibition can be overcome by increasing [S]
  • Km appears to increase in presence of inhibitor; Vmax does not change
32
Q

Noncompetitive Inhibitors

A
  • bind to a site on the enzyme other than the active site
  • inhibition cannot be overcome by increasing [S]
  • Vmax appears to decrease in the presence of inhibitor; Km does not change
33
Q

What does the Ki mean?

A
  1. It quantifies the strength with which an inhibitor binds to an enzyme
  2. It is the dissociation constant for the enzyme-inhibitor complex
34
Q

T or F: Higher Ki implies weaker inhibition

A

True

35
Q

A graph of 1/[S] (x axis) and 1/v (y axis) and several [I] (inhibitors) plotted, will intersect at the y axis if I is a ___ inhibitor

A

competitive

36
Q

A graph of 1/[S] (x axis) and 1/v (y axis) and several [I] (inhibitors) plotted, will intersect at the x axis if I is a ___ inhibitor

A

non-competitive

37
Q

T or F: Doubling enzyme (and thus Vmax) changes the Km

A

False

Gotcha ;-D

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