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BIO NMDCAT

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Practice Questions

In a multistep enzyme mechanism, the overall reaction rate is determined by the step with the

A. Lowest activation energy
B. Highest activation energy
C. Greatest entropy change
D. Largest number of water molecules
nmdcat.online BIO NMDCAT
Jul 11, 2026

In glyceraldehyde 3 phosphate dehydrogenase, the catalytic cysteine is activated by a neighboring

A. Aspartate
B. Histidine
C. Zinc ion
D. Arginine
nmdcat.online BIO NMDCAT
Jul 11, 2026

Stabilization of a negatively charged tetrahedral intermediate is achieved by the

A. Hydrophobic pocket
B. Oxyanion hole
C. Zinc ion
D. Allosteric site
nmdcat.online BIO NMDCAT
Jul 11, 2026

Pepsin has an optimum pH of about 2 because

A. Its coenzyme works only at low pH
B. Catalytic residues require a specific protonation state
C. The substrate is active only at pH 2
D. Product inhibition occurs at higher pH
nmdcat.online BIO NMDCAT
Jul 11, 2026

Stereospecificity in enzyme action means the enzyme can

A. Change its own stereochemistry
B. Produce racemic products
C. Distinguish between optical isomers and act on only one
D. Convert every substrate into its optical isomer
nmdcat.online BIO NMDCAT
Jul 11, 2026

In aldolase, formation of a Schiff base between lysine and the substrate is an example of

A. Cofactor mediated catalysis
B. Covalent catalysis
C. Metal ion catalysis
D. General acid catalysis
nmdcat.online BIO NMDCAT
Jul 11, 2026

Vmax of an enzyme catalyzed reaction is reached when

A. The enzyme is denatured
B. Product concentration becomes zero
C. Further increase in substrate concentration fails to increase the reaction rate
D. Km becomes zero
nmdcat.online BIO NMDCAT
Jul 11, 2026

Observation of a burst phase of rapid product formation followed by a slower steady state phase suggests

A. Random sequential binding
B. Rate limiting formation of a covalent enzyme substrate intermediate
C. Rate limiting release of the first product
D. Slow activation of the free enzyme
nmdcat.online BIO NMDCAT
Jul 11, 2026

The active site of an enzyme is usually located in a deep cleft or pocket because it

A. Protects the enzyme from phosphorylation
B. Provides a large flat surface for adsorption
C. Sequesters the substrate from bulk solvent and creates a specialized environment
D. Allows simultaneous binding to DNA and proteins
nmdcat.online BIO NMDCAT
Jul 11, 2026

A Lineweaver Burk plot supporting a ping pong mechanism shows

A. Lines intersecting on the x axis
B. Parallel lines at varying substrate concentrations
C. A single straight line
D. A sigmoidal curve
nmdcat.online BIO NMDCAT
Jul 11, 2026

The active site of an enzyme is often described as a “microenvironment.” A key characteristic of this microenvironment is

A. A completely uniform charge distribution
B. A significantly lowered dielectric constant that enhances electrostatic interactions
C. A pH always equal to 7.0
D. An unlimited supply of free water molecules
nmdcat.online BIO NMDCAT
Jul 11, 2026

A Bi substrate reaction following a Sequential Ordered mechanism is characterized by

A. Random substrate binding
B. Both substrates bind before any product is released, in a compulsory order
C. Product leaves before all substrates bind
D. Reaction rate is independent of the second substrate
nmdcat.online BIO NMDCAT
Jul 11, 2026

An enzyme that catalyzes reactions without any non protein component relies solely on

A. Quaternary structure
B. Amino acid side chains arranged in the active site
C. Alpha helices
D. Signal peptide
nmdcat.online BIO NMDCAT
Jul 11, 2026

The x intercept of a Lineweaver Burk plot equals

A. -1/Vmax
B. -1/Km
C. Vmax/Km
D. Km/Vmax
nmdcat.online BIO NMDCAT
Jul 11, 2026

In lysozyme, Glu35 remains protonated because its microenvironment is

A. Highly hydrophilic
B. Hydrophobic and non polar
C. Rich in lysine residues
D. Completely neutral
nmdcat.online BIO NMDCAT
Jul 11, 2026

A ping pong mechanism refers to a kinetic sequence where

A. Substrate inhibits product
B. One product is released before all substrates bind
C. Cooperative binding occurs
D. Non competitive inhibition occurs
nmdcat.online BIO NMDCAT
Jul 11, 2026

Formation of a covalent enzyme substrate intermediate after the first product leaves is characteristic of

A. Sequential ordered mechanism
B. Sequential random mechanism
C. Ping pong double displacement mechanism
D. Concerted acid base mechanism
nmdcat.online BIO NMDCAT
Jul 11, 2026

During the mechanism of chymotrypsin, the “pong” step involves

A. Release of the unaltered second substrate
B. Binding of a water molecule and its nucleophilic attack on the acyl enzyme intermediate
C. Binding of an allosteric inhibitor
D. Auto degradation of the enzyme
nmdcat.online BIO NMDCAT
Jul 11, 2026

The catalytic efficiency of an enzyme is best described by the ratio

A. Kcat / Vmax
B. Km / Kcat
C. Kcat / Km
D. Vmax / Kcat
nmdcat.online BIO NMDCAT
Jul 11, 2026
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