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 determine if a protein sample contains disulfide bonds. Which experimental approach would best allow her to do this?

Accepted Answer

Run SDS-PAGE under both reducing and non-reducing conditions and compare the band patterns.

Question 3

Which of the following best describes the role of 2-mercaptoethanol (BME) or dithiothreitol (DTT) in protein analysis?

Accepted Answer

They reduce disulfide bonds, converting them to free thiols ($$\ce{R-S-S-R + 2HS-CH2CH(OH)CH2OH -\u003e 2R-SH + HOCH2CH(OH)CH2-S-S-CH2CH(OH)CH2OH}).$$

Question 4

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

Accepted Answer

Covalent bonds between backbone atoms (excluding disulfide bonds)

Question 5

A patient’s hemoglobin shows a higher than normal P50 value. What does this indicate about the hemoglobin’s oxygen binding affinity?

Accepted Answer

The hemoglobin has a lower affinity for oxygen.

Question 6

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 $$O_2$$, facilitating oxygen release in tissues.

Question 7

Which of the following is a key difference between hemoglobin and myoglobin?

Accepted Answer

Hemoglobin exhibits cooperative oxygen binding, while myoglobin does not.

Question 8

Which of the following best describes the effect of 2,3-bisphosphoglycerate (2,3-BPG) on hemoglobin?

Accepted Answer

2,3-BPG binds to hemoglobin and stabilizes the T state, decreasing oxygen affinity.

Question 9

A mutation in the proximal histidine (His F8) of hemoglobin to glycine (H93G) results in which of the following?

Accepted Answer

Increased oxygen affinity due to decoupling of the F helix from the heme group.

Question 10

Which of the following best describes a Southern blot?

Accepted Answer

A technique used to detect specific DNA sequences using a labeled DNA probe.

Question 11

Which of the following is true regarding antibody-antigen interactions?

Accepted Answer

They are mediated by shape and charge complementarity, involving hydrogen bonds, van der Waals, and ionic interactions.

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 Ser substitution at position 143, favoring the R state.

Question 13

Which of the following best describes the difference between homotropic and heterotropic allosteric effectors?

Accepted Answer

Homotropic effectors bind at the active site, while heterotropic effectors bind at other sites.

Question 14

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

Accepted Answer

The patient is generally asymptomatic except under oxygen stress, and has increased resistance to malaria.

Question 15

Which of the following best describes the Hill equation for cooperative ligand binding?

Accepted Answer

$$YO_2 = \frac{PO_2^n}{P_{50}^n + PO_2^n}$$ where $$n is $$the Hill coefficient indicating cooperativity.

Question 16

Which of the following is a key feature of the MWC (Monod-Wyman-Changeux) model of hemoglobin allostery?

Accepted Answer

Hemoglobin exists in equilibrium between T and R states, and all subunits switch states simultaneously.

Question 17

Which of the following best describes the function of the complementarity-determining regions (CDRs) in antibodies?

Accepted Answer

They form the hypervariable loops that directly interact with the antigen.

Question 18

Which of the following best explains why guanidinium chloride is not used as a denaturant in electrophoresis?

Accepted Answer

It is highly charged and used at high concentrations, which interferes with electrophoresis.

Question 19

Which of the following best describes the principle behind Western blotting?

Accepted Answer

Proteins are separated by electrophoresis, transferred to a membrane, and detected with specific antibodies.

Protein Function and Evolution: Structure, Analysis, and Allosteric Regulation

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