Ch6 Adaptive Quiz: Enzymes 6.3-6.4 Flashcards
What does the y intercept on a Lineweaver-Burk plot represent?
1/Vmax
Which enzyme catalyzes polyamine synthesis in trypanosomes, the parasite that causes African sleeping sickness?
ornithine decarboxylase
In drug development, enzyme inhibition studies play a very important role since drugs are often used to target specific enzymes, as illustrated in the example of lovastatin. An important consideration when assessing drug potential is the drug’s affinity for the selected target. (The higher the affinity, the better the candidate.) The KI is often used in studies to measure the affinity of drug candidates toward their target. Based on your understanding of KI, which drug would be the BEST candidate for further development?
Drug B: KI = 2.5 × 10−6 mM
What is clavulanic acid’s mechanism of action?
β-Lactamase’s Ser residue forms a covalent adduct with the drug’s β-lactam ring to irreversibly acylate the enzyme and inactivate it.
Does enolase require a cofactor or a coenzyme?
cofactor; Mg2+
The rate limiting step of an enzyme-catalyzed reaction:
has a rate constant equal to kcat.
Which statement is false regarding the burst phase of chymotrypsin catalysis?
The acylation step produces one molecule of acetic acid.
Does ornithine decarboxylase, the catalytic enzyme responsible for trypanosome polyamine synthesis, require a cofactor or a coenzyme?
coenzyme
At a substrate concentration that is much greater than the Km for the reaction, which statement is true (assuming the enzyme obeys Michaelis-Menten kinetics)?
The reaction velocity is equal to Vmax.
In deriving the Michaelis-Menten equation for enzyme kinetics, what is the steady-state assumption?
[ES] is constant.
Carboxypeptidase A, which has a Zn2+ ion cofactor in its active site, breaks down protein during metabolism. To which major subclass of proteases does carboxypeptidase A belong?
metalloprotease
When a substrate and enzyme are mixed, what happens during the pre–steady state?
The concentration of the enzyme-substrate complex increases until it reaches a constant level.
Which chemical structure is a common biochemical nucleophile?
imidazole
Which three amino acids form the catalytic triad in chymotrypsin?
Ser, Asp, His
Chymotrypsin:
uses the oxygen of a serine side chain as a nucleophile.
What is the steady state?
the reaction period where [ES] is constant
How is the Michaelis constant, Km, defined?
the substrate concentration at which V0 is half-maximal
Which enzyme has the highest catalytic efficiency?
Enzyme A: Km = 2.5 μM; Vmax = 100 mM/min
If Vmax is 100.0 μM/min using an enzyme concentration of 0.1 μM, what is kcat for the reaction?
1,000 min−1.
k cat= V max/[E]
