$$\text{pH} = \text{p}K_a + \log \left( \frac{[\text{HCO}_3^-]}{[\text{H}_2\text{CO}_3]} \right)$$

Question 1

Which equation correctly represents the equilibrium for the binding of a ligand (L) to a protein (P) to form a protein-ligand complex (PL)?

Accepted Answer

$$P + L \rightleftharpoons PL$$

Question 2

The dissociation constant $$K_d$$ for a protein-ligand interaction is defined as:

Accepted Answer

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

Question 3

If the affinity of a protein for its ligand increases, what happens to the dissociation constant $$K_d$$?

Accepted Answer

$$K_d$$ decreases

Question 4

Which of the following best explains why ligand binding to a protein is typically reversible?

Accepted Answer

Ligands bind through non-covalent interactions, allowing them to dissociate from the protein.

Question 5

The fraction of protein binding sites occupied by ligand ($$Y) is $$given by which equation?

Accepted Answer

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

Question 6

When $$[L] = K_d$$, what is the value of $$Y ($$the fraction of protein binding sites occupied by ligand)?

Accepted Answer

$$Y = 0.5$$

Question 7

Which statement best describes the effect of 2,3-BPG binding to hemoglobin?

Accepted Answer

2,3-BPG stabilizes the T-state of hemoglobin, decreasing its affinity for oxygen.

Question 8

Why does carbon monoxide (CO) bind more tightly to hemoglobin than oxygen?

Accepted Answer

CO binds to the iron atom in heme with a much higher affinity than oxygen due to its linear geometry.

Question 9

What is the physiological significance of the Bohr Effect in hemoglobin?

Accepted Answer

It allows hemoglobin to release more oxygen in tissues with low pH and high CO$$_2$$ concentration.

Question 10

Which amino acid residue in hemoglobin is critical for stabilizing the T-state through salt bridge formation?

Accepted Answer

His HC3

Question 11

At pH 7.4, what fraction of His HC3 is protonated in deoxyhemoglobin if its pK$$_a is 7.8$$?

Accepted Answer

$$\frac{1}{1 + 10$$^{(7.4-7.8)}$$} = \frac{1}{1 + 0.25} = 0.80 ($$about 80%)

Question 12

Why is oxygen binding to hemoglobin considered cooperative, while myoglobin does not show cooperativity?

Accepted Answer

Hemoglobin has multiple subunits that communicate conformational changes, while myoglobin is monomeric.

Question 13

Which equation is used to calculate the pH of blood serum using the carbonic acid/bicarbonate buffer system?

Accepted Answer

$$	ext{pH} = 	ext{p}K_a + \log \left( \frac{[	ext{HCO}_3^-]}{[	ext{H}_2	ext{CO}_3]} ight)$$

Question 14

What is the effect of hyperventilation on blood pH?

Accepted Answer

It increases blood pH, making it more alkaline due to excessive loss of CO$$_2.$$

Question 15

Which of the following best describes the role of His E7 in hemoglobin?

Accepted Answer

It sterically interferes with CO binding, reducing CO affinity.

Question 16

What is the main reason why hemoglobin releases oxygen more efficiently in tissues than myoglobin?

Accepted Answer

Hemoglobin's cooperative binding allows it to release a larger fraction of its oxygen load at lower oxygen pressures.

Question 17

Which of the following is an example of an allosteric effector for hemoglobin?

Accepted Answer

2,3-BPG

Question 18

What happens to the pK$$_a of $$His HC3 in hemoglobin after it moves from the T-state to the R-state?

Accepted Answer

It decreases to its normal value, and the side chain becomes mostly deprotonated.

Question 19

Which of the following best explains why the oxygen binding curve for hemoglobin is sigmoidal (S-shaped)?

Accepted Answer

Cooperative binding between subunits causes a gradual increase in affinity as more oxygen binds.

Protein-Ligand Binding and Hemoglobin Function: Biochemistry Study Notes

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