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BIO NMDCAT

1785 questions found

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Practice Questions

Ribonuclease A provides a classic example of general acid base catalysis using

A. Two aspartates
B. Two tyrosines
C. Two histidines
D. Two cysteines
nmdcat.online BIO NMDCAT
Jul 11, 2026

The concept of electrostatic catalysis involves active site residues

A. Forming transient covalent bonds
B. Using charged side chains to stabilize charge in the transition state
C. Creating a completely non polar environment
D. Mechanically unfolding the substrate
nmdcat.online BIO NMDCAT
Jul 11, 2026

An enzyme fully saturated with substrate is operating at Vmax. At this stage, the rate limiting step is most likely

A. Initial substrate binding
B. Diffusion of enzyme and substrate
C. Chemical conversion of substrate into product
D. Product release
nmdcat.online BIO NMDCAT
Jul 11, 2026

The involvement of an enzyme in a reaction means the reaction pathway will have

A. More intermediate steps with lower activation energy barriers
B. Fewer intermediate steps
C. A single step without a transition state
D. Higher activation energy
nmdcat.online BIO NMDCAT
Jul 11, 2026

During catalysis by hexokinase, glucose binding causes enzyme lobes to close around the substrate. This supports the

A. Lock and key model
B. Allosteric regulation
C. Induced fit model
D. Covalent catalysis
nmdcat.online BIO NMDCAT
Jul 11, 2026

The specific region where substrate binds and catalysis occurs is the

A. Allosteric site
B. Active site
C. Coenzyme binding domain
D. Signal sequence
nmdcat.online BIO NMDCAT
Jul 11, 2026

An amino acid residue acting as a proton donor performs the role of

A. Nucleophilic catalyst
B. Metal ion cofactor
C. General acid catalyst
D. Allosteric modulator
nmdcat.online BIO NMDCAT
Jul 11, 2026

Amino acid residues that directly participate in bond making and bond breaking are called

A. Structural residues
B. Catalytic residues
C. Binding residues
D. Regulatory residues
nmdcat.online BIO NMDCAT
Jul 11, 2026

The reaction mechanism of lysozyme involves the distortion of a sugar ring into a strained “sofa” conformation. This illustrates the catalytic strategy of

A. Providing a macroenvironment that neutralizes all charges on the substrate
B. Using covalent catalysis to form a stable enzyme substrate intermediate
C. Preferentially binding and stabilizing the transition state of the reaction
D. Lowering the pH of the bulk solution to non specifically hydrolyze the substrate
nmdcat.online BIO NMDCAT
Jul 11, 2026

The mechanism by which the active site of an enzyme lowers the activation energy does NOT include

A. Providing a microenvironment different from the bulk aqueous solution
B. Orienting the substrates precisely for a reaction
C. Increasing the local concentration of substrates
D. Permanently increasing the average kinetic energy of the substrate population
nmdcat.online BIO NMDCAT
Jul 11, 2026

In the catalytic mechanism of serine proteases, the role of the histidine residue in the catalytic triad is to function as a

A. Strong nucleophile
B. Binding site for hydrophobic side chains
C. General base catalyst
D. Metal chelating ligand
nmdcat.online BIO NMDCAT
Jul 11, 2026

The formation of a transient acyl enzyme intermediate during chymotrypsin catalysis is an example of

A. Acid base catalysis
B. Electrostatic catalysis
C. Covalent catalysis
D. Metal ion catalysis
nmdcat.online BIO NMDCAT
Jul 11, 2026

The proximity effect in enzyme catalysis refers to the enzyme’s ability to

A. Attract substrates from distant cells
B. Bind substrates close together and in the correct orientation
C. Generate a new substrate molecule
D. Increase proximity to regulatory molecules
nmdcat.online BIO NMDCAT
Jul 11, 2026

The mechanism of enzyme action fundamentally depends on the enzyme’s ability to

A. Increase the kinetic energy of all molecules in the reaction mixture
B. Provide a surface with a specific shape and chemical groups for the substrate
C. Alter the standard free energy change to make the reaction exergonic
D. Combine permanently with the product to shift the equilibrium forward
nmdcat.online BIO NMDCAT
Jul 11, 2026

The binding of a substrate to an enzyme’s active site is predominantly mediated by

A. Strong, irreversible covalent bonds
B. Weak, non covalent interactions that allow transient and reversible binding
C. Permanent dipole moments
D. Hydrophobic forces excluding all water
nmdcat.online BIO NMDCAT
Jul 11, 2026

The lock and key model, proposed by Emil Fischer, describes enzyme substrate interaction as

A. A flexible active site
B. A rigid, pre shaped active site complementary to the substrate
C. Random collision followed by substrate change
D. Substrate changes enzyme primary structure
nmdcat.online BIO NMDCAT
Jul 11, 2026

A key limitation of the lock and key model is its inability to explain

A. High substrate specificity
B. Dependence of reaction rate on substrate concentration
C. Ability of the enzyme to stabilize the transition state
D. Formation of enzyme substrate complex
nmdcat.online BIO NMDCAT
Jul 11, 2026

The induced fit model proposed by Daniel Koshland suggests that the active site

A. Is permanently complementary to the product
B. Undergoes conformational change upon substrate binding
C. Is always rigid
D. Is located on a separate regulatory subunit
nmdcat.online BIO NMDCAT
Jul 11, 2026

Regarding the chemical nature of an enzyme, the most accurate statement is that

A. All enzymes are simple proteins
B. The catalytic activity of some enzymes is inherent in their RNA component
C. Enzymes are exclusively multimeric proteins
D. The catalytic site of any enzyme requires a specific lipid prosthetic group

The discovery of ribozymes (RNA catalysts) disproved the long-held belief that all enzymes are proteins.

nmdcat.online BIO NMDCAT
Jul 11, 2026
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