Biochem Test 2
B
A heterotropic activator will have what effect on a sigmoidal kinetic plot (v vs. [S])? A) The curve will shift to the right. B) The curve will shift to the left. C) The curve will become more sigmoidal. (The first half will be decreased and the second half increased.) D) The curve will become hyperbolic.
peptide
A proteolytic enzyme cleaves _____ bonds.
It will increase 20 fold
A reaction has an equilibrium constant, Keq, of 50. When performed in the presence of an appropriate enzyme, the forward rate constant is increased 20-fold. What will happen to the reverse rate constant?
1. Tells how much substrate will saturate E 2. The stability (the rate dissociation of ES complex divided by the rate of formation of the ES complex) of the ES complex
According to the Briggs and Haldane view of enzyme kinetics in 1925, what two things does the Km tell you about an enzyme reaction?
A
Catalysis by an enzyme can occur if which of the following happens? A) The activation energy is decreased in the presence of the enzyme. B) The activation energy is increased in the presence of the enzyme. C) The free energy of the product is higher than the free energy of the substrate in the presence of the enzyme. D) The ΔG of the reaction in the absence of the enzyme minus the ΔG of the reaction in the presence of the enzyme is less than zero.
No
Do enzymes affect Keq?
No
Do enzymes make unfavorable reactions favorable?
substrate specificity
In 1890 Emil Fischer introduced the idea of a 'lock and key' to describe what?
ES complex to explain the hyperbolic rate curve of enzymes.
In 1902, Brown and Henri expanded Fischer's 'lock and key' to invoke what kind of complex? What was their evidence?
B
In a double-reciprocal or Lineweaver-Burk plot, the KM is found from A) y-intercept = -1/KM. B) x-intercept = -1/KM. C) slope = KM. D) y-intercept = -Vmax/KM. E) x-intercept = -Vmax/KM.
D
In a system at equilibrium: A) there is no net change in the concentrations of the products and reactants. B) ΔG is zero. C) ΔG‡ is zero. D) there is no net change in the concentrations of the products and reactants and ΔG is zero.
C
On what basis are enzymes and proteins with allosteric properties different from those without allosteric properties? A) on the basis of having more than one subunit B) on the basis of having different responses to non-substrate molecules such as inhibitors C) on the basis of their different dependence on substrate concentration D) on the basis of having more than one substrate-binding site
induced fit
The alteration of enzyme structure on binding of a substrate to an active site is referred to as
A
The effects of molecules other than substrate on allosteric enzymes are called A) heterotropic effects. B) homotropic effects. C) allosteric effects. D) competitive effects.
D
The study of the rates of enzyme-catalyzed reactions: A) is called enzyme kinetics. B) can involve determining how fast the substrate disappears as it is converted to product. C) can involve following the appearance of product formed over time. D) All of the above
D
The ΔG° is the standard free-energy change when the concentration of each reactant is: A) equal to the concentration of all other reactants. B) equal to 1mM. C) equal to 1M. D) equal to both the concentration of all other reactants and 1M.
C
To obtain k2, the turnover number of an enzyme, one must A) divide Vmax by 2. B) divide v by Vmax. C) divide Vmax by the total enzyme concentration. D) divide Vmax by kcat.
A
Vmax, the maximum velocity, of an enzyme-catalyzed reaction is A) the rate observed when all enzyme active sites are saturated with substrate. B) independent of the amount of enzyme present. C) the rate observed at the highest substrate concentration that can be experimentally obtained. D) the initial rate observed at very low substrate concentrations.
It means that at the beginning it is first order with respect to substrate but after all of the enzymes are taken it becomes zero order.
What does the rectangular hyperbola mean for a rate curve?
The fastest rate that the enzyme can turnover (make product)
What is Vmax according to Michaelis and Menten's treatment?
Inactive precursors of enzymes -activated by specific proteolysis
What is a zymogen?
An enzyme mechanism is a chemical model describing how an enzyme reduces activation energy.
What is an enzyme mechanism?
The rate constant of the rate-limiting step (the moles of substrate converted per second)
What is kcat ?
The time for a single catalytic event
What is kcat's inverse?
Second order reactions that can appear to be first order reactions (reaction velocity is directly related to the concentration of the reactant)
What is meant by 'pseudo-first order'?
Pseudo-first order
What is the order of the reaction relative to [E]?
Linear
What is the shape of the curve if [S] is sat'd and [E] is varied?
The order of enzymatic reactions: the forward rate constant dependence on [S]
What is unique about the order of enzyme reactions?
Rate is limited by the stability of the transition state relative to the reactants.
What limits the rate of an uncatalyzed reaction?
it must be negative
What must be true of the free-energy change, ΔG, for a reaction to be spontaneous?
Zero order because the reactant is high so the reaction does not depend on reactant concentration.
What order is an enzyme reaction at high [S]? What does that mean?
They thought it was the dissociation constant
What was M&M's mistake with Km?
A
When k-1 > k2 (that is, when the rate constant for dissociation of the enzyme substrate complex is greater than the rate constant for conversion to product), the KM is most analogous to A) the Kd. B) the Ka. C) the kcat. D) 1/kcat.
B
Which of the following is TRUE regarding a Michaelis-Menten kinetics graph? A) The x-axis is "time." B) The x-axis is "substrate concentration." C) The y-axis is "product concentration." D) Both the first and third answers are true.
A
Which of the following is true of a holoenzyme but not an apoenzyme? A) contains a cofactor B) is catalytically inactive C) contains a denatured active site D) contains more than one active site
D
Which of the following statements is TRUE of carbonic anhydrase? A) It catalyzes a reaction involving water. B) It catalyzes a reaction involving CO2. C) It is a very fast enzyme. D) All of the above
B
Which of the following statements is true regarding the role an enzyme plays in catalysis? A) An enzyme increases the equilibrium constant. B) An enzyme decreases the activation energy. C) An enzyme increases the energy of the transition state so that it breaks down more rapidly. D) An enzyme increases the rate of the forward reaction.
Because we are only looking at the initial rates (v0)
Why can we ignore the reverse reaction when we are determining the rate constants for enzymes?
