Chapter 5: Protein Function

Question 1

What are the two types of interactions?

Answer 1

1. Protein acting as a reaction catalyst, or enzyme.

2. Neither the chemical configuration nor the composition of the bound molecule has changed.

Question 2

Where does a ligand bind?

Answer 2

The binding site at a protein

Question 3

What is an induced fit?

Answer 3

The structural adaptation occurs between protein and ligand.

Question 4

Describe two things about Oxygen?

Answer 4

1. Poorly soluble in aqueous solution.

2. Transitions metals have a strong tendency to bind.

Question 5

What is a heme?

Answer 5

Protein-bound prosthetic group

Question 6

Would a molecule of Oxygen bind to one of the hemes of a hemoglobin molecules in the T state, which has no molecules of Oxygen bound?

Answer 6

Yes, but the molecules of Oxygen would bind weakly because the T state has a low affinity for Oxygen.

Question 7

What happens when one molecules of Oxygen binds to hemoglobin?

Answer 7

The affinity of neighboring subunits of Oxygen increases.

Question 8

Can a molecule of Oxygen dissociate from one of the hemes of a hemoglobin molecule in the R state, which has four molecules of Oxygen bound?

Answer 8

Yes, but dissociation is difficult because the R state has a high affinity for Oxygen.

Question 9

What happens when one molecule of Oxygen dissociates from hemoglobin?

Answer 9

The affinity for Oxygen of neighboring subunits decreases.

Question 10

Under which condition does hemoglobin primarily exist in the T state?

Answer 10

Low Oxygen concentration

Question 11

Based on how Oxygen binding affects the affinity of neighboring hemoglobin subunits , Oxygen is an _____ allosteric modulator.

Answer 11

Activating homotropic.

Question 12

Which methods of energy production contributes to a decrease in pH?

Answer 12

Both aerobic and anaerobic metabolism.

Question 13

What increases and decreases during vigorous exercise, in terms of physiological factors.

Answer 13

CO2 concentration increases.

Oxygen concentration decreases and pH decreases.

Question 14

Physiological changes favoring the T state.

Answer 14

1. Decreased pH
2. Increased CO2 concentration.
3. Decreased Oxygen concentration.

Question 15

The combination of decreased O2 concentration, an increased CO2 concentration, and a decrease pH led to the football player’s sickle cell crisis.

Based on this information, the football player’s sickle cell crisis was most likely triggered by the aggregation of hemoglobin in which state?

Answer 15

The T state

Question 16

Considering the structure of 2,3‑BPG, what type of residues do you suspect line the cavity between the β subunits where 2,3‑BPG binds?

Answer 16

Positively charged residues. Because 2,3-BPG is deprotonated and negatively charged.

Question 17

Which state of hemoglobin would predominate if the blood concentration of 2,3 BPG increases?

Answer 17

The T State.
Because 2, 3 BPG sits in the central cavity between the Beta subunits of the T state tetramer. That cavity is closed in the R state.

Question 18

What would be the net effect of increasing the concentration of 2,3 BPG in the blood?

Answer 18

Hemoglobin’s affinity for Oxygen would decrease.

Question 19

Why are the His residues in the central cavity Hba important for the binding of 2,3 BPG?

Answer 19

The His residues can become protonated and positively charged, enabling the to strongly interact with the negatively charged groups of 2,3 BPG.

Question 20

How should replacing His residues found in HbA with Her residues found in HbF affect the binding of 2,3 BPG to HbF?

Answer 20

HbF should have a lower affinity for 2,3 BPG relative to HbA.

Question 21

Since CO2 binds to hemoglobin like Oxygen, what is the effect of one molecule of CO binding to hemoglobin?

Answer 21

The affinity of neighboring subunits for both Oxygen and CO increases.

Question 22

Which conformational state for hemoglobin should have a higher affinity for CO?

Answer 22

The R state.

Question 23

Favoring conditions of R state of hemoglobin.

Answer 23

High Oxygen concentration and high CO concentration.