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Biomolecules

Satisfactory Essays

Chapter 4: Protein Function
Chapter 7, Voet, Voet & Pratt * Link between protein structure and physiological function * Focus on myoglobin and hemoglobin * Both proteins reversibly bind to O2 * Extremely well-studied examples of structure/function relationships * Behavior is a model for many other proteins, especially metabolic enzymes
Learning Objectives * Compare myoglobin and hemoglobin * Structures * Properties * O2 binding characteristics * Understand structural basis for hemoglobin’s O2 binding characteristics * Relate these characteristics to physiological role of hemoglobin * Understand biochemical basis of diseases/adaptations involving hemoglobin
O2 Binding …show more content…

1. Binding of O2causes the Fe(II) to move into the plane of the porphyrin. 2. Movement of the Fe(II) and flattening of the porphyrin forces Helix F to shift (~1Å)

3. The shift of the Helix F causes the 3° structure of the subunit to change, which in turn affects how the protomers interact * Specifically at the α1 – β2 interface during the T R transition

4. The subunit structural changes reduce the number of salt-pair interactions at their C-terminals

Their conformational change caused by oxygen binding tears these ionic interactions apart.
The Bohr Effect Enhances O2 Transport * Decreases the pH induces Hb to bind less O2 at lower oxygen pressures * Conformational changes that occur on O2 binding alter the pKa’s of several groups: * N-terminal α-subunit * C-terminal Histidine of β-subunit
In the T-state, these units participate in ion bridges; raising their pKa’s
In the R-state, they are not in ion-pairs; pKa’s decrease and become more acidic * Hb releases ~0.6 protons per O2 bound

When we increase the pH, the concentration of protons increase and there is an increase of Hb and the t-state

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