Chapter 11: Q12P (page 359)
Question: Explain why RNase A cannot catalyze the hydrolysis of DNA
Answer
DNA does not have the 2’-OH group which is required for hydrolyzing into intermediates like 2’,3’-cyclic nucleotides
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Using the reaction shown in Box 11-1 (the attack of an amine on thecarbonyl group of a ketone) as a starting point, draw curved arrows torepresent the acid-catalyzed reaction (when the group —A—H is present).
Studies at different pH’s show that an enzyme has two catalytically important residues whose pKs are ~4 and ~10. Chemical modification experiments indicate that a Glu and a Lys residue are essential for activity. Match the residues to their pKs and explain whether they are likely to act as acid or base catalysts.
Hemophiliacs who lack factor IX are sometimes given infusions of factor VII to restore normal blood clotting activity. Explain.
On the free energy diagram shown, label the intermediate(s) and transition state(s). Is the reaction thermodynamically favorable?
Lysozyme residues Asp 101 and Arg 114 are required for efficient catalysis, although they are located some distance from the active sites Glu 35 and Asp 52. Substituting Ala for either Asp 101 or Arg 114 does not significantly alter the enzyme’s tertiary structure, but it significantly reduces its catalytic activity. Explain.
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