Studies on the catalytic activity of hexokinase provided the following data: Which experiment would contain the greatest percentage of folded protein?

Question

Studies on the catalytic activity of hexokinase provided the following data:  Which experiment would contain the greatest percentage of folded protein?

Quizplus · Accepted Answer

11ecba2d_0e36_f4b9_a3bf_d9cbc6cf6c5e_MD0008_00 Proteins have evolved to function within a narrow range of cellular conditions. Enzymes, in particular, can remain functional only when their three-dimensional shape, or tertiary structure, is maintained. Noncovalent interactions, such as hydrogen bonds, ionic bonding, and hydrophobic effects, allow proteins to fold into secondary structures (α-helices and β-sheets) that combine to form tertiary structures. The disruption of noncovalent bonds that causes proteins to unfold and lose their function is referred to as denaturation. Proteins unfold rapidly at conditions outside their optimal range because denaturation is a cooperative process. Although heat energy increases the rate of a reaction, high temperatures can also cause denaturation. The excess kinetic energy provided by increasing temperatures generates vibrations that disrupt hydrogen bonding between polar atoms and hydrophobic interactions in nonpolar regions. Denaturation also occurs in the presence of urea, which is a polar amide produced by protein metabolism and excreted by the body. Urea induces the unfolding of proteins by exposing hydrophobic groups and interfering with hydrogen bonding in the amino acid backbone. Proteins exposed to high temperatures and concentrations of urea unfold easily and lose their function. Therefore, high temperatures and urea concentrations decrease the reaction rate, indicating a smaller percentage of folded protein. Of the choices listed, Experiment II provides the best conditions for enzymatic function because the temperature and urea concentration are within a range that results in the highest reaction rate. Consequently, Experiment II must contain the highest percentage of folded protein. (Choices A, C, and D) The high temperatures and/or urea concentrations in these experiments cause a large percentage of hexokinase proteins to unfold, as reflected by the low enzymatic activity under these conditions. Educational objective: Enzymatic function is maintained by noncovalent interactions in the tertiary and secondary structure of proteins. Noncovalent interactions such as hydrogen bonding and hydrophobic effects are disrupted by high temperatures and high concentrations of urea. Proteins lose functionality when their tertiary structure unfolds (denaturation).

Studies on the Catalytic Activity of Hexokinase Provided the Following