Question 1

Which of the following best describes the difference between the primary and secondary structure of a protein?

Accepted Answer

Primary structure refers to the sequence of amino acids, while secondary structure refers to local folding patterns such as $$\alpha-$$helices and $$\beta-$$sheets stabilized by hydrogen bonds.

Question 2

Which of the following interactions is NOT primarily responsible for stabilizing the tertiary structure of a protein?

Accepted Answer

Peptide bonds

Question 3

A Ramachandran plot is used to:

Accepted Answer

Visualize the allowed values of $$\phi$$ and $$\psi$$ dihedral angles in a polypeptide backbone.

Question 4

Which statement best explains why molecular chaperones are necessary for some proteins to fold correctly?

Accepted Answer

They prevent aggregation and misfolding by stabilizing unfolded or partially folded proteins.

Question 5

Which of the following conditions is most likely to cause protein denaturation?

Accepted Answer

Extreme pH changes

Question 6

Which technique would be most appropriate to determine the atomic-resolution 3D structure of a small, soluble protein?

Accepted Answer

X-ray crystallography

Question 7

The Bohr effect describes how:

Accepted Answer

A decrease in pH or an increase in $$\mathrm{CO}_2$$ concentration reduces hemoglobin's affinity for oxygen, facilitating oxygen release in tissues.

Question 8

Which of the following best explains why hemoglobin exhibits positive cooperativity in oxygen binding?

Accepted Answer

Binding of one $$\mathrm{O}_2$$ molecule increases the affinity of the remaining subunits for $$\mathrm{O}_2$$ due to conformational changes from the T to R state.

Question 9

Given a ligand-binding curve for a protein, the dissociation constant $$K_d is $$defined as:

Accepted Answer

The ligand concentration at which half of the binding sites are occupied.

Question 10

A patient with sickle cell anemia has a mutation in hemoglobin where glutamate is replaced by valine at position 6 of the $$\beta-$$chain. This mutation leads to:

Accepted Answer

Hydrophobic interactions between hemoglobin molecules, causing aggregation and sickling of red blood cells.

Question 11

Which of the following statements about enzyme catalysis is correct?

Accepted Answer

Enzymes lower the activation energy ($$\Delta G$$^{\ddagger}$$) of a reaction without changing the overall free energy change ($$\Delta G$$).

Question 12

Which of the following is an example of a prosthetic group?

Accepted Answer

Heme in cytochrome c

Question 13

The Michaelis–Menten equation is given by

$$V_0$$ = \frac{V_{max}[S]}{K_m + [S]}$$

If $$[S] \gg K_m$$, what is the approximate value of V_0$?

Accepted Answer

$$V_0$$ \approx V_{max}$$

Question 14

Which of the following best describes the induced fit model of enzyme catalysis?

Accepted Answer

The enzyme changes shape upon substrate binding to better stabilize the transition state.

Question 15

A Lineweaver-Burk plot is a double reciprocal plot of enzyme kinetics. Which equation describes this plot?

Accepted Answer

$$\frac{1}{V_0$} = \frac{K_m}{V_{max}} \cdot \frac{1}{[S]} + \frac{1}{V_{max}}$$

Question 16

Which of the following is most likely to decrease the activity of an enzyme whose active site contains a histidine residue essential for catalysis?

Accepted Answer

Lowering the pH below the p$$K_a of $$histidine, causing it to become fully protonated.

Question 17

Which of the following statements about the effect of 2,3-BPG on hemoglobin is correct?

Accepted Answer

2,3-BPG binds to deoxyhemoglobin, stabilizing the T state and decreasing oxygen affinity.

Question 18

Which of the following best distinguishes between homotropic and heterotropic allosteric modulators?

Accepted Answer

Homotropic modulators are the substrate itself, while heterotropic modulators are different molecules that bind allosteric sites.

Question 19

Which of the following best explains why fetal hemoglobin (HbF) has a higher oxygen affinity than adult hemoglobin (HbA)?

Accepted Answer

HbF binds 2,3-BPG less tightly than HbA, resulting in a higher oxygen affinity.

Protein Structure, Function, and Enzyme Catalysis: Study Guide

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