Question 1

Which of the following best defines a 'ligand' in the context of protein-ligand interactions?

Accepted Answer

A molecule that binds specifically and reversibly to a protein, often affecting its function.

Question 2

Which intermolecular force is primarily responsible for the specificity of ligand binding to proteins?

Accepted Answer

Hydrogen bonding

Question 3

Given the dissociation constant $K_d$ for the binding of a ligand to a protein, which equation correctly relates $K_d$ to the concentrations of the protein-ligand complex, free protein, and free ligand?

Accepted Answer

$K_d = \frac{[P][L]}{[PL]}$

Question 4

If the ligand concentration $[L]$ is equal to the dissociation constant $K_d$, what is the fractional saturation ($Y$) of the protein?

Accepted Answer

$Y = 0.5$

Question 5

Why do vertebrate animals require oxygen carriers such as myoglobin and hemoglobin?

Accepted Answer

Because oxygen is poorly soluble in water and cannot be transported efficiently without carriers.

Question 6

Which interaction is most responsible for oxygen binding to the heme group in myoglobin and hemoglobin?

Accepted Answer

Coordination bond between oxygen and the iron atom in heme.

Question 7

Which statement best explains the difference between the oxygen binding curves of myoglobin and hemoglobin?

Accepted Answer

Hemoglobin shows a sigmoidal curve due to cooperative binding, while myoglobin shows a hyperbolic curve.

Question 8

Which physiological advantage does the sigmoidal oxygen binding curve of hemoglobin provide?

Accepted Answer

It enables efficient oxygen loading in the lungs and unloading in tissues.

Question 9

What is the effect of 2,3-BPG (2,3-bisphosphoglycerate) on hemoglobin's oxygen binding affinity?

Accepted Answer

It decreases hemoglobin's affinity for oxygen, promoting oxygen release in tissues.

Question 10

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

Accepted Answer

Hemoglobin releases oxygen more readily at low pH and high carbon dioxide concentration.

Question 11

Explain 'cooperative' oxygen binding in hemoglobin. Which of the following statements is correct?

Accepted Answer

Binding of one oxygen molecule increases the affinity for subsequent oxygen molecules.

Question 12

Which equation best describes the equilibrium between the T (tense) and R (relaxed) states of hemoglobin?

Accepted Answer

$T \rightleftharpoons R$

Question 13

Sickle-cell anemia is caused by a mutation in hemoglobin. Which biochemical change is responsible for the disease?

Accepted Answer

A substitution of glutamic acid with valine in the beta chain of hemoglobin.

Question 14

Which physiological consequence is most directly associated with sickle-cell anemia?

Accepted Answer

Decreased solubility of deoxygenated hemoglobin, leading to cell sickling and blockage of blood vessels.

Question 15

Which commercial drug is used to treat altitude sickness by promoting oxygen release from hemoglobin?

Accepted Answer

Diamox (acetazolamide)

Question 16

Which laboratory technique is commonly used to detect proteins by immunoblotting?

Accepted Answer

Western blotting

Question 17

A patient with chronic lung disease has elevated levels of 2,3-BPG. What is the expected effect on their hemoglobin oxygen binding curve?

Accepted Answer

The curve shifts to the right, indicating decreased oxygen affinity.

Question 18

Which of the following best describes the role of myoglobin in muscle tissue?

Accepted Answer

It stores oxygen for use during periods of high metabolic activity.

Question 19

Which of the following is NOT a consequence of the Bohr effect?

Accepted Answer

Increased oxygen affinity at low pH.

Reversible Binding of a Protein to a Ligand: Oxygen-Binding Proteins

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