Test 3 Flashcards
(41 cards)
How does a catalyst increase the rate of reaction?
it allows reacting molecules to more easily form the transition state
Which of the following amino acids would be most likely found in the active site of an enzyme that uses acid-base catalysis
Histidine
In an enzyme mechanism that generates a negative energy charge in the transition state, which of the following would be most effective to have in the active site of the enzyme?
Transition metal cation
If the Asp of the chymotrypsin active site was mutated to another amino acid, which of the following would be considered an invisible mutation in that it is least likely to impact the function of the enzyme?
Asp –> Glu
During the first half of the chymotrypsin mechanism where the acyl-enzyme intermediate is formed, what role does His play?
general base then general acid
When the transition state is formed, what is the specific interaction observed between Asp and His that helps stabilize the transition state?
low-barrier hydrogen bond
A plot of velocity versus substrate concentration for a simple enzyme-catalyzed reaction produces a _______. This indicates that at some point, the enzyme is _____.
Hyperbolic curve; saturated with substrate
How is the enzyme-catalyzed reaction affected by the addition of more enzyme?
Velocity will increase
Which of the following must be true if the steady state assumption is to be used?
d[ES]/dt = 0
An extremely efficient enzyme has a _____ Km and a _____ Kcat.
small; large
Enzyme studies were conducted for tryosinase enzyme in the presence and absence of the inhibitor dodecyl gallate, as illustrated in the plots below. What is the value of the Km in the ABSENCE inhibitor?
For Lineweaver plot, Km is calculated from the x-intercept. Hence Km = 1mM
An inhibitor of aldehyde dehydrogenase was designed. The Michaelis-Menten plot of the enzyme activity without and with two different concentrations of inhibitor is below. What is the Km and Vmax values for each of the assay samples based off the Michaelis-Menten plot?
VMax doesn’t change, Km is 1/2 of Vmax on the line
A positive deltaG means what for spontaneity?
Unfavorable; unspontaneous
A negative deltaG means what for spontaneity?
Spontaneous reaction
What is glyceraldehyde-3-phosphate dehydrogenase doing in this reaction? (Glycolysis)
Catalyzing the reaction
If this reaction was carried out at 25C, what would be the equilibrium constant for the reaction be? Remember -DeltaG = RT ln K, R =8.315 J/mol X K
Change the delta G to JOULES instead of KJ; so -6300 J/mol = 8.315 J/mol (298K) lnK
Solving for K: Keq = 0.078
What are coupled reactions? Illustrate with an example.
Whenever a thermodynamically UNFAVORABLE reaction (deltaG Positive) is paired with favorable reaction (deltaG negative) or in other words spontaneous reaction drives the overall non-spontaneous one. Example Hexokinase reaction.
Which of the following represents the net products of glycolysis from ONE molecule of glucose?
2 pyruvate, 2 NADH, 2 ATP
With a deltaG of -16.7 kJ/mol, the reaction catalyzed by hexokinase is considered to be
Metabolically irreversible
Which of the following enzymes requires ATP as a substrate?
phosphofructokinase
What enzyme catalyzes the major regulatory step of glycolysis?
phosphofructokinase
Which of the following is a potent activator of phosphofructokinase in mammals?
fructose-2,6-biphosphate
The enzyme responsible for the synthesis of fructose-2,6-biphosphate is ____.
phosphofructokinase-2
Triose phosphate isomerase catalyzes a reaction that is most similar to _____.
phosphoglucose isomerase
