Lecture 6 DA Flashcards Preview

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Flashcards in Lecture 6 DA Deck (14)
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1
Q

What are two ways an enzyme can obtain energy neccessary for catalysis?

A

>Binding energy - The binding of the substrate to the enzyme can give sufficient energy.

>Can also use entropy by positioning molecules together precisely, such as hydrolysis reactions positioning water molecules precisely.

2
Q

What kind of curve does an enzyme reaction rate curve have, and what dominates the linear phase? What dominates the non-linear phase, and what kind of curve does it represent? Which reactions represent each phase?

A

The curve as a whole is hyperbolic. The early linear phase is dominated by the reaction E+S=ES, a second order reaction. As it gets closer to Vmax, it becomes a logarithmic curve, and is dominated by the first order reaction ES(=EP)=E+P

3
Q

What is the formula for v (rate of reaction)? Why is this so?

A

v=[ES]*k2

It measures breakdown of ES to E+P

4
Q

What are the inherent assumptions of the michaelis menten equation ()? Why are they assumed?

A

-That [S] is far far greater than [E]. >Important as the equation relies on free [S], and not [ES] as well. Given [E] is so small, [ES] and its effect is negligible. -That [P] is effectively 0. >P may not have enough time to accumulate in experiments, and given its similarity to S, may inhibit the enzyme. May also shift the equilibrium. -That [E] and [S] are in equilibrium, called the equilibrium assumption. In reality, it is below the equilibrium, k2, but this is assumed to be negligible.

5
Q

What is the equilibrium assumption? What is the reality of the equilibrium, and is it significant?

A

The equilibrium is the assumption that [E] and [S] are in equilibrium. In reailty, the equilibrium is below k2, but is not significant and assumed to be negligible.

6
Q

What isoenzyme of hexokinase does the brain, and why? Whats different about the enzyme that it uses this isoform instead? What is normally used in the liver?

A

The brain uses the isoform hexokinase I, which is important for periods of low glucose levels, which is its sole source of energy (aside from ketone bodies). This isoform has a much higher affinity for glucose versus liver isoforms, so it receives enough glucose despite the shortage. The liver uses the isoform glucokinase, also called hexokinase IV.

7
Q

What equation is the lineweaver-burk plot represented by?

A
8
Q

What do the x and y intercepts of the lineweaver burk plot represent? What is the gradient of the curve?

A

y intercept = 1/Vmax

x intercept = -1/km

Gradient = km/Vmax

9
Q

What is a disadvantage of the lineweaver-burk plot?

A

It is dominated by points at low [S], and high 1/s.

10
Q

What type of curves do allosteric enzymes produce?

A

Sigmoidal curves.

11
Q

Do allosteric enzyme curves depend on the michaelis menten equation?

A

No, they depend on the Vo of [S].

12
Q

What is the effect of competitive, uncompetitive and, non-competitive inhibition on Km and Vmax? What effect does substrate overload have on these inhibitions?

A

Competitive inhibition

  • Km increases, Vmax is unaffected
  • Substrate overload can overturn inhibition effects.

Uncompetitive inhibition

  • Reduces Vmax, reduces Km.
  • Substrate overload doesn’t overcome inhibition effects.

Non-competitive inhibition

-Reduces Vmax, Km is unaffected.

13
Q

What is the difference between competitive, non-competitve and, uncompetitive inhibition?

A

Competitive -Binds to the active site of the enzyme. Uncompetitive -Binds only to the ES complex. Non-competitive -Binds allosterically to the enzyme to reduce activity.

14
Q

What does a higher or smaller Km or Ki value represent regarding affinity?

A

The smaller the Km/Ki value, the tighter the binding, and so the higher the affinity.