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Binding Site Saturation

Does the concentration of a ligand determine the rate of protein-mediated process? Proteins perform a variety of cellular functions. Some proteins are structural. Others function in transport across membranes and in catalyzing reactions (enzymes). Transport proteins and enzymes have active sites, specific areas of the protein that bind to and interact with other molecules. The other molecules are known as ligands. Protein functions such as transport and catalysis have rates which are determined by the physical and chemical conditions in the cellular environment as well as the relative number of protein and ligand molecules.

View the animation below, then complete the quiz to test your knowledge of the concept.






1Initially, as the ligand concentration rises...
A)the receptor proteins rapidly become saturated.
B)the rate of binding to the receptor proteins remains the same.
C)the binding to the receptor proteins is inversely proportional to the concentration of ligand available.
D)the rate of binding to the receptor proteins increases.
E)the rate of binding to the receptor proteins decreases.



2Eventually...
A)more receptor sites become available for the ligands to bind to.
B)all of the receptor proteins become tied up.
C)more receptor sites are synthesized to handle the increased load.
D)ligand concentrations are reduced by negative feedback.
E)ligand concentrations are reduced by positive feedback.



3As saturation is reached...
A)the rate of binding to the receptor proteins increases.
B)the rate of binding to the receptor proteins decreases.
C)more receptor sites become available for the ligands to bind to.
D)more receptor sites are synthesized to handle the increased load.
E)the receptor proteins cannot bind to the ligand molecules any faster, even if more ligand is added.



4Prior to reaching the point of saturation, there are always receptor sites available for ligand binding.
A)True
B)False



5When the receptor proteins are saturated, no more are available to handle the increased demand.
A)True
B)False







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