1. An effective respiratory carrier protein must be able to pick up oxygen from

Question

1.         An effective respiratory carrier protein must be able to pick up oxygen from the lungs and deliver it to the peripheral tissues. Two oxygen dissociation curves for proteins A and B are shown below. Explain whether or not each of these is an effective carrier.

If your answer is “neither one”, show on the same figure, where the curve for an effective carrier would be. Data: pO2 = 100 torr in the lungs and 20 torr in the tissues.

2.         If a substrate were to have equal affinities for the T and R forms of an allosteric enzyme, what would happen to the kinetics of this enzyme? In addition to explaining in words, also show your answer graphically.          

3.         Predict whether each of the following conditions will increase or decrease the tendency of HbS molecules to polymerize in vitro. Give your rationale for each answer.

            (a) Increase in temperature

            (b) Increase in partial pressure of oxygen

            (c) Removing 2,3-BPG from the HbS molecule

            (d) Increase in pH

Explanation / Answer

b) Increase in partial pressure of oxygen

In some intracellular compartments, X may be surrounded by a variety of other soluble macromolecules that cumulatively occupy a significant fraction of the total volume (Fulton, 1982). Since no single macromolecular species need be present at high concentration, such media are referred to as crowded or volume occupied rather than concentrated (Minton and Wilf, 1981). Since macromolecules cannot interpenetrate, the fraction of volume into which a macromolecule can be placed at any instant is much less than the fraction of volume into which a small molecule can be placed (Fig. 2A,B). The total free energy of interaction between X and all of the other molecules in the crowded medium is inversely related to the probability of successful placement of X at a random location within the crowded medium (Lebowitz et al., 1965). Hence the extra work required to transfer X from a dilute to a crowded solution resulting from steric repulsion between X and background molecules depends upon the relative sizes and shapes of X and background species, and increases in a highly nonlinear fashion with increasing size of X and with fractional volume occupancy

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