Biochemistry: Chapter 6
Which statement is false regarding the initial velocity of an enzymatic reaction?
(correct) A.) Initial velocity increases linearly with substrate concentrations when substrate concentrations are high. B.) Only 2-3% of the substrate converts to product during initial velocity. C.) Substrate concentration is considered constant at the very beginning of the reaction. D.) Initial velocity is a function of the substrate concentration.
Which statement is false regarding activation energy, ΔG′°?
(correct) A.) Raising the temperature of a reaction lowers the activation energy. B.) Increasing the pressure provides energy to overcome the reaction activation energy. C.) Adding an enzyme to the reaction lowers the activation energy. D.) A higher activation energy corresponds to a slower reaction.
Which answer choice specifies the correct order of events in the mechanism of action of HIV protease?
1. Attack of the carbonyl carbon by water. 2. Formation of a tetrahedral intermediate. 3. Protonation of the amino acid leaving group.
What does the y intercept on a Lineweaver-Burk plot represent?
1/Vmax
At a substrate concentration of 5 mM, what is the velocity of an enzymatic reaction using a Lineweaver-Burk plot with a slope of 0.02 min and a y intercept of 0.04 min/mM?
23 mM/min
Succinyl-CoA transferase catalyzes a reaction that has a Keq of 0.040. What is the standard free-energy change for this reaction?
7.98 kJ/mol
Which statement is false regarding chymotrypsin's mechanism of action as a protease?
A.) Low pH causes His57 protonation, effectively preventing proton extraction from Ser195. (correct) B.) His57 protonates the acetyl leaving group, allowing the acetic acid product to dissociate from the enzyme. C.)Hydrogen bonding between His57, Ser195, and Asp102 forms a catalytic triad. D.) The side chain of a peptide substrate fits into a hydrophobic pocket to situate the peptide bond for cleavage.
Which statement is false regarding coenzymes?
A.) Most coenzymes require organic nutrient precursors ingested in small amounts from the diet. B.) Coenzymes are transient carriers of special functional groups. (correct) C.) Riboflavin is a coenzyme. D.) Vitamin B1 is the precursor of thiamine pyrophosphate. E.) Pyridoxal phosphate transfers amino groups.
Which statement is false regarding allosteric enzyme kinetics?
A.) Plots of V0 versus [S] produce sigmoid saturation curves. B.) The symbol [S]0.5 is equal to K0.5. C.) When the substrate concentration is high, the kinetics curve saturates. (correct) D.) The substrate concentration at half-maximal velocity is the Km value.
Which pairing correctly matches the enzyme class with the type of reaction it catalyzes?
A.) lyase: formation of C—C, C—S, C—O, and C—N bonds by condensation reactions B.) ligase: cleavage of C—C, C—O, C—N, or other bonds by elimination, leaving double bonds C.) hydrolase: group transfer (correct) D.) oxidoreductase: transfer of electrons
Hepatic glucose 6-phosphatase, the enzyme responsible for releasing glucose into the blood, has a pH optimum of about 7.8. Normal hepatocyte pH is about 7.2. What happens to this phosphatase activity in a patient diagnosed with acidosis due to chronic alcohol use?
Activity will decrease due to the decrease in pH
What is the current theory behind the substrate-enzyme interaction in the enzyme's active site?
The active site is complementary to the transition state.
Which statement is false about β lactam antibiotics?
They are reversible inhibitors.
Which statement is false regarding covalent modification for enzyme regulation?
Zymogenation is a type of covalent regulatory modification.
In deriving the Michaelis-Menten equation for enzyme kinetics, what is the steady-state assumption?
[ES] is constant
Which antibiotic(s) do drug-resistant bacteria inactivate?
all known β-lactam antibiotics
What is a coenzyme?
an organic or metalloorganic group, often derived from a vitamin, that is essential for enzyme function
Which component of the ATCase reaction brings about the conformational change from the inactive T state to the active R state?
aspartate and carbamoyl phosphate
Which enzyme mechanism involves a nucleophilic attack on the substrate from an enzyme component?
covalent catalysis
Which cellular component is a common coenzyme?
flavin adenine dinucleotide
What causes hexokinase to conformationally change into its catalytically active form?
glucose and the Mg · ATP complex binding to the enzyme
ATCase catalyzes the conversion of carbamoyl phosphate and aspartate into N-carbamoylaspartate, a precursor in pyrimidine biosynthesis. What roles do ATP and CTP play in this reaction?
heterotropic modulators
When oxygen binds to hemoglobin, the protein's conformation changes to make additional oxygen binding sites available. What role does oxygen play in this interaction?
homotropic modulator
If the free-energy change for a reaction decreases due to changes in the conditions, what happens to the equilibrium constant?
it increases
Which coenzyme is NOT paired with its correct dietary precursor?
niacin → nicotinamide adenine dinucleotide vitamin B1 → thiamine pyrophosphate (correct) vitamin B6 → tetrahydrofolate pantothenic acid → coenzyme A riboflavin → flavin adenine dinucleotide
Which coenzyme is NOT paired with its correct dietary precursor?
pantothenic acid → coenzyme A vitamin B1 → thiamine pyrophosphate niacin → nicotinamide adenine dinucleotide vitamin B9 → tetrahydrofolate (correct) vitamin B12 → flavin adenine dinucleotide
An apoenzyme:
requires a cofactor for its activity.
How is the Michaelis constant, Km, defined?
the substrate concentration at which V0 is half-maximal
Which coenzyme is NOT paired with its correct dietary precursor?
vitamin B7 → coenzyme A
