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🧬AP Biology
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🧬AP Biology

FRQ 4 – Conceptual Analysis (Short)
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Unit 1: Chemistry of Life
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Practice FRQ 1 of 171/17

4. Cytosolic proteins, such as the enzyme hexokinase, function within the water-filled cytoplasm of cells. These proteins fold into specific three-dimensional shapes based on the sequence of amino acids in their polypeptide chains. The stability of this folded tertiary structure depends heavily on the chemical interactions between the amino acid side chains (R-groups) and the surrounding aqueous environment.

A research team creates a variant of hexokinase in which a serine residue located on the surface of the protein is replaced with a phenylalanine residue.

A.

Describe the chemical property of water molecules that allows them to function as a solvent for the hydrophilic regions of a protein.

B.

Explain how the properties of nonpolar amino acid R-groups contribute to the formation of the protein's tertiary structure in an aqueous environment.

Scientists engineer a variant of the hexokinase protein to study protein stability. In the wild-type protein, residue 152 is a serine, which is a polar amino acid located on the exterior surface of the folded protein. In the variant protein, this serine is replaced by a phenylalanine, which is a nonpolar amino acid.

C.

Predict the effect of the serine-to-phenylalanine substitution on the solubility of the variant protein in the cytoplasm compared to the wild-type.

D.

Justify your prediction in part C.

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