Question 1

Which statement best describes the concept of 'induced fit' in protein-ligand interactions?

Accepted Answer

The protein undergoes a conformational change that makes the binding site more complementary to the ligand, resulting in tighter binding.

Question 2

A protein binds a ligand reversibly according to the equilibrium $$P + L \rightleftharpoons PL. If $$the association constant $$K_a is $$high, what does this indicate about the protein-ligand interaction?

Accepted Answer

The protein has a high affinity for the ligand.

Question 3

Which of the following is TRUE regarding the specificity of protein-ligand binding?

Accepted Answer

Binding sites are complementary to the ligand in size, shape, charge, and hydrophobic/hydrophilic character.

Question 4

Hemoglobin exhibits cooperative binding of oxygen. Which of the following best explains this phenomenon?

Accepted Answer

Binding of oxygen to one subunit increases the affinity of the remaining subunits for oxygen.

Question 5

The Hill coefficient ($$n_H) $$for a newly discovered protein with multiple subunits and positive cooperativity is:

Accepted Answer

Greater than 1.

Question 6

Which molecule acts as a homotropic modulator in the binding of oxygen to hemoglobin?

Accepted Answer

Oxygen

Question 7

A patient is exposed to high levels of carbon monoxide (CO). Why is CO dangerous in terms of hemoglobin function?

Accepted Answer

CO binds to the heme group of hemoglobin with much higher affinity than oxygen, displacing oxygen and impairing oxygen delivery to tissues.

Question 8

Which of the following best describes the Bohr effect?

Accepted Answer

An increase in pH and decrease in CO$$_2$$ concentration increases hemoglobin's affinity for oxygen.

Question 9

Which equation describes the fraction of occupied ligand-binding sites ($$Y) $$for a protein binding a ligand $$L$$ with dissociation constant $$K_d$$?

Accepted Answer

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

Question 10

At what value of $$[L] is $$half of the available ligand-binding sites occupied ($$Y = 0.5) $$for a protein-ligand system?

Accepted Answer

$$[L] = K_d$$

Question 11

Which of the following statements about myoglobin is CORRECT?

Accepted Answer

Myoglobin consists mostly of alpha helices and contains a single binding site for oxygen.

Question 12

A protein has a $$K_d$$ for ligand $$L of$$ $$10^{-9} M$$, while another protein has a $$K_d of$$ $$10^{-6} M $$for the same ligand. Which protein has the higher affinity for $$L$$?

Accepted Answer

The protein with $$K_d = 10$$^{-9}$$ M

Question 13

Which of the following is a consequence of hemoglobin's quaternary structure?

Accepted Answer

Conformational changes in one subunit can affect the binding properties of other subunits.

Question 14

Which molecule acts as a heterotropic allosteric modulator of hemoglobin, decreasing its affinity for oxygen and facilitating oxygen release in tissues?

Accepted Answer

2,3-Bisphosphoglycerate (BPG)

Question 15

During vigorous exercise, muscle tissue experiences hypoxia. Which adaptation helps hemoglobin deliver more oxygen to tissues under these conditions?

Accepted Answer

Increase in BPG concentration, which lowers hemoglobin's affinity for oxygen

Question 16

Which of the following best describes the role of the distal histidine (His E7) in myoglobin?

Accepted Answer

It forms a hydrogen bond with bound oxygen, stabilizing the O$$_2$$ complex and reducing CO binding affinity.

Question 17

Which of the following is TRUE regarding the effect of pH on hemoglobin's oxygen binding curve?

Accepted Answer

A decrease in pH shifts the curve to the right, decreasing hemoglobin's affinity for oxygen.

Question 18

Which equation represents the Hill equation for cooperative ligand binding?

Accepted Answer

$$\log \left( \frac{Y}{1-Y} \right) = n \log [L] - \log K_d$$

Question 19

Which laboratory technique uses antibodies to detect specific proteins in a sample?

Accepted Answer

Western blot (immunoblot)

Protein Function: Principles and Oxygen-Binding Proteins

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