Hemoglobin (Hb) can be viewed as having two quaternary states, a low oxygen affi

Question

Hemoglobin (Hb) can be viewed as having two quaternary states, a low oxygen affinity state (T), and a high oxygen affinity state (R). Which of the following statements about the binding of O2 by Hb are true?

1) Upon binding a molecule of oxygen, Hb undergoes a conformational change that makes the binding of subsequent O2 molecules easier.
2) The conformational change induced in Hb upon binding oxygen is the result of a small movement (0.2 Å) of the iron cation in the center of heme.
3) Site-directed mutagenesis studies have indicated that the cooperativity of O2 binding in Hb is attributable to the movement of the F helix in Hb.
4) Site-directed mutagenesis studies in which the proximal His residues of the F helix have been replaced by glycines have indicated the mutant protein still shows cooperativity of O2 binding.

Hemoglobin (Hb) can be viewed as having two quaternary states, a low oxygen affinity state (T), and a high oxygen affinity state (R). Which of the following statements about the binding of O2 by Hb are true?

1) Upon binding a molecule of oxygen, Hb undergoes a conformational change that makes the binding of subsequent O2 molecules easier.
2) The conformational change induced in Hb upon binding oxygen is the result of a small movement (0.2 Å) of the iron cation in the center of heme.
3) Site-directed mutagenesis studies have indicated that the cooperativity of O2 binding in Hb is attributable to the movement of the F helix in Hb.
4) Site-directed mutagenesis studies in which the proximal His residues of the F helix have been replaced by glycines have indicated the mutant protein still shows cooperativity of O2 binding.

Only statements 1, 2, and 4 are true. Only statements 1, 3, and 4 are true. Only statements 1, 2, and 3 are true. All of the listed statements are true.

Explanation / Answer

Only statements 1, 2, and 3 are true.

Since proximal His residues directly attached to the F helix, cooperativity couldn't be acheived when it's replaced by glycine residues.

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