Question 1

Which of the following statements best explains why proteins migrate according to their molecular weight in SDS-PAGE, but not in native PAGE?

Accepted Answer

SDS binds to proteins, giving them a uniform negative charge and denaturing them, so migration depends only on size.

Question 2

A researcher wants to separate a protein into its individual polypeptide chains and analyze their sizes. Which combination of reagents and techniques should she use?

Accepted Answer

SDS and a reducing agent (such as DTT or β-mercaptoethanol) followed by SDS-PAGE.

Question 3

Which of the following interactions is NOT a major contributor to the stabilization of protein tertiary structure?

Accepted Answer

Covalent bonds between side chains (other than disulfide bonds).

Question 4

In the context of antibody structure, what is the function of the Fab fragment?

Accepted Answer

It contains the antigen-binding site and is responsible for recognizing specific epitopes.

Question 5

Which of the following best describes the Bohr effect in hemoglobin?

Accepted Answer

A decrease in pH (increase in H+) decreases hemoglobin's affinity for O2, facilitating O2 release in tissues.

Question 6

A patient has a mutation in the proximal histidine (His F8) of hemoglobin, replacing it with glycine (H93G). What is the most likely effect on oxygen binding?

Accepted Answer

The mutant hemoglobin will have a higher affinity for oxygen due to decoupling of the F helix from the heme group.

Question 7

Which of the following is a negative heterotropic allosteric effector of hemoglobin?

Accepted Answer

2,3-bisphosphoglycerate (2,3-BPG)

Question 8

A protein sample is analyzed by both SDS-PAGE and native PAGE. The SDS-PAGE shows a single band at 25 kDa, while the native PAGE shows a band at 100 kDa. What is the most likely explanation?

Accepted Answer

The protein is a tetramer of 25 kDa subunits.

Question 9

Which of the following best describes the difference between Southern, Northern, and Western blotting techniques?

Accepted Answer

Southern blot detects DNA, Northern blot detects RNA, Western blot detects protein.

Question 10

The oxygen binding curve for myoglobin is hyperbolic, while that for hemoglobin is sigmoidal. What is the physiological significance of this difference?

Accepted Answer

Hemoglobin's sigmoidal curve allows for cooperative binding and efficient O2 delivery to tissues.

Question 11

Which equation correctly describes the fractional saturation ($$Y_{O_2$}) of $$myoglobin with oxygen?

Accepted Answer

$$Y_{O_2$} = \frac{P_{O_2$}}{P_{50} + P_{O_2$}}$$

Question 12

Which of the following best explains why fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin?

Accepted Answer

Fetal hemoglobin binds 2,3-BPG less tightly due to a Ser143 substitution, favoring the R state.

Question 13

Which of the following is a correct statement about the Hill coefficient ($$n) in $$the Hill equation for hemoglobin?

Accepted Answer

A Hill coefficient greater than 1 indicates positive cooperativity in O2 binding.

Question 14

Which of the following best describes the molecular mechanism underlying the T to R transition in hemoglobin?

Accepted Answer

O2 binding pulls Fe2+ into the heme plane, causing conformational changes that disrupt salt bridges and favor the R state.

Question 15

Which of the following is a real-world application of the high specificity of antibodies?

Accepted Answer

Targeted delivery of drugs to specific cells in antibody-drug conjugates.

Question 16

A patient with sickle-cell disease is found to be heterozygous for the sickle-cell mutation. What is a likely consequence?

Accepted Answer

The patient is generally asymptomatic but has increased resistance to malaria.

Question 17

Which of the following best describes the role of 2,3-BPG in oxygen delivery by hemoglobin?

Accepted Answer

2,3-BPG binds to hemoglobin and stabilizes the T state, promoting O2 release in tissues.

Protein Function and Evolution: Analytical Methods, Antibody Structure, and Hemoglobin Allostery

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