A) WHERE (in/on the hemoglobin molecule) and HOW (what kinds of bonds/interactio

Question

A) WHERE (in/on the hemoglobin molecule) and HOW (what kinds of bonds/interactions) does 2,3-bisphosphoglycerate (BPG) interact with hemoglobin?

B) Does it INCREASE or DECREASE Hb's affinity for O2?

C) Myoglobin, and the individual subunits of hemoglobin, are similar, though certainly not identical, in size, overall shape, and function. A comparison of the structure of myoglobin to that of a single subunit of hemoglobin shows their tertiary structure similarity: Myoglobin Single subunit of Hemoglobin

Which of the two polypeptides, a molecule of myoglobin or a subunit of hemoglobin, would you expect to have a greater ratio of nonpolar : polar amino acids? Why?

D) The Bohr effect for oxygen binding states that

A. Mb binds oxygen more tightly than Hb.

B. as the pH goes down, Hb binds oxygen less tightly.

C. Hb will bind oxygen very tightly when the CO2 concentration is high.

D. Hb's ability to bind oxygen increases with higher oxygen concentration.

E) Which of the following statements are true concerning the structures of hemoglobin and myoglobin and their O2-binding site? If a statement is FALSE, explain WHY.

1) The iron in heme in both proteins binds oxygen reversibly.

2) The iron in heme in both molecules binds to five nitrogen atoms and to oxygen.

3) Myoglobin has a similar tertiary structure to a subunit of hemoglobin.

4) Myoglobin has a similar quaternary structure to a subunit of hemoglobin

5) Myoglobin could substitute for one of the subunits in hemoglobin in red blood cells.

6) Myoglobin contains one binding site for oxygen per molecule

7) Myoglobin contains one binding site for oxygen per heme

8) Hemoglobin contains one binding site for oxygen per complete protein molecule

9) Hemoglobin contains one binding site for oxygen per polypeptide subunit.

1. WHERE (in/on the hemoglobin molecule) and HOW (what kinds of bonds.l interactions) does 2,3-bisphosphoglycerate (BPG) interact with hemoglobin? Where? (1 pt) How? (1 pt) 3.Does it INCREASE or DECREASE Hb's affinity for 02?

Explanation / Answer

Answer a) A single molecule of 2,3- bisphosphoglycerate (2,3- BPG) binds to a pocket formed by two beta globin chains in the centre of the taut form of deoxyhaemoglobin tetramer and stabilizes it. This pocket contains several positively charged amino acids which interact to form ionic bonds with negatively charged amino acids of 2,3- BPG.

Answer b) The binding of 2,3- BPG significantly decreases the affinity of haemoglobin for oxygen and enables the haemoglobin to efficiently release oxygen at the partial pressure present in the tissues.

Answer c) Haemoglobin has a higher ratio of non-polar to polar amino acids than myoglobin. Haemoglobin has four subunits and they need to interact with each other mainly through hydrophobic interactions. Therefore, non-polar amino acids residues on the surface help in these interactions. Myoglobin is a single subunit and has more of hydrophilic amino acid residues i.e. polar amino acids.

Answer d) The Bohr effect for oxygen binding states that as the pH goes down Hb binds oxygen less tightly.

The oxygen binding affinity of haemoglobin is inversely related to both acidity ( decrease in pH) and concentration of carbon dioxide.

Answer e) 1. True

2. False. The iron in heme in both molecules binds to four nitrogen atoms.

3. True

4. False. Myoglobin has a similar tertiary structure to subunit of haemoglobin

5. False.

6. True

7. True

8. False. Hemoglobin contains four binding sites for oxygen per complete protein molecule

9. True

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