Lecture 6 DA Flashcards
What are two ways an enzyme can obtain energy neccessary for catalysis?
>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.
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?
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
What is the formula for v (rate of reaction)? Why is this so?
v=[ES]*k2
It measures breakdown of ES to E+P
What are the inherent assumptions of the michaelis menten equation ()? Why are they assumed?
-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.
What is the equilibrium assumption? What is the reality of the equilibrium, and is it significant?
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.
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?
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.
What equation is the lineweaver-burk plot represented by?
What do the x and y intercepts of the lineweaver burk plot represent? What is the gradient of the curve?
y intercept = 1/Vmax
x intercept = -1/km
Gradient = km/Vmax
What is a disadvantage of the lineweaver-burk plot?
It is dominated by points at low [S], and high 1/s.
What type of curves do allosteric enzymes produce?
Sigmoidal curves.
Do allosteric enzyme curves depend on the michaelis menten equation?
No, they depend on the Vo of [S].
What is the effect of competitive, uncompetitive and, non-competitive inhibition on Km and Vmax? What effect does substrate overload have on these inhibitions?
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.
What is the difference between competitive, non-competitve and, uncompetitive inhibition?
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.
What does a higher or smaller Km or Ki value represent regarding affinity?
The smaller the Km/Ki value, the tighter the binding, and so the higher the affinity.
