Question 1

Which of the following statements best explains why SDS-PAGE separates proteins primarily by molecular weight?

Accepted Answer

SDS binds to proteins, giving them a uniform negative charge and denaturing them into rod-like shapes, so migration depends mainly on size.

Question 2

A researcher wants to determine if a protein sample contains disulfide bonds. Which gel electrophoresis conditions should they use to distinguish between proteins with and without disulfide bonds?

Accepted Answer

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

Question 3

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

Accepted Answer

Covalent bonds between backbone amide groups.

Question 4

Which statement correctly describes the difference between a Southern blot and a Western blot?

Accepted Answer

A Southern blot detects specific DNA sequences, while a Western blot detects specific proteins using antibodies.

Question 5

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

Accepted Answer

A decrease in pH (increase in $$[H^+]) $$stabilizes the T state, lowering hemoglobin's affinity for $$O_2$$ and promoting oxygen release.

Question 6

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

Accepted Answer

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

Question 7

A patient with a mutation in the proximal histidine (H93G) of hemoglobin shows higher oxygen affinity than normal. What is the most likely explanation?

Accepted Answer

The mutation decouples the F helix from the heme, reducing the energy barrier for the T to R transition and increasing $$O_2$$ affinity.

Question 8

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

Accepted Answer

Fetal hemoglobin binds BPG less tightly due to a Ser 143 substitution, favoring the R state and increasing $$O_2$$ affinity.

Question 9

Which of the following best describes the oxygen binding curve of myoglobin compared to hemoglobin?

Accepted Answer

Myoglobin has a hyperbolic binding curve, while hemoglobin has a sigmoidal binding curve due to cooperativity.

Question 10

Which of the following statements about allosteric regulation in hemoglobin is correct?

Accepted Answer

Oxygen is a positive homotropic effector because its binding increases the affinity of other subunits for oxygen.

Question 11

A mutation causes hemoglobin to have a much lower $$P_{50}$$ value than normal. What is the physiological consequence?

Accepted Answer

Hemoglobin will bind $$O_2$$ more tightly, making it less efficient at releasing $$O_2 to $$tissues.

Question 12

Which of the following best describes the structural change in hemoglobin during the T to R transition?

Accepted Answer

Oxygen binding pulls the $$Fe^{2+}$$ ion into the plane of the heme, causing a shift in the F helix and a 15° rotation between subunits.

Question 13

Which of the following is true regarding the role of 2,3-bisphosphoglycerate (BPG) in oxygen transport?

Accepted Answer

BPG binds to the central cavity of deoxyhemoglobin, stabilizing the T state and promoting oxygen release.

Question 14

A patient is hyperventilating, leading to decreased $$CO_2$$ levels in the blood. What is the expected effect on hemoglobin's oxygen affinity and tissue oxygen delivery?

Accepted Answer

Hemoglobin's affinity for $$O_2$$ increases, resulting in less efficient oxygen delivery to tissues.

Question 15

Which of the following best describes the difference between myoglobin and hemoglobin in terms of structure and function?

Accepted Answer

Myoglobin is a monomer that stores $$O_2 in $$muscle, while hemoglobin is a tetramer that transports $$O_2 in $$blood.

Question 16

Which of the following best explains why sickle-cell disease provides resistance to malaria?

Accepted Answer

Heterozygotes for the sickle-cell mutation are asymptomatic except under oxygen stress, which impairs malaria parasite survival in red blood cells.

Question 17

Which of the following is a key feature of the immunoglobulin fold found in antibodies?

Accepted Answer

It is a beta-sandwich composed of two beta sheets stacked face to face.

Question 18

Which of the following best describes the complementarity-determining regions (CDRs) of an antibody?

Accepted Answer

They are hypervariable loops at the ends of the variable regions that determine antigen specificity.

Protein Function and Evolution: Structure, Analysis, and Hemoglobin Allostery

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