Q38 - Molecular Clock Estimates of Substitution Counts, Divergence Time and Domain-Specific Rates
Zuckerkandl and Pauling proposed the molecular clock hypothesis, in which amino acid differences in a protein accumulate at a uniform rate among species. The rate of amino acid substitution varies among proteins because of differences in functional importance. Proteins X (400 a.a., substitution rate 0.625 x 10^-9 substitutions/site/ year) and Y (600 a.a., substitution rate 1.25 x 10^-9 substitutions/site/year).
Using the information and data, determine which of the statements are true or which are false.
A. In each of proteins X and Y, how many substitutions were expected to accumulate at maximum between human and mouse, which diverged 80 million years ago (MYA)?
B. In Protein X, 6 amino acid substitutions were observed between human and a mammal species. Choose the right choice for the divergence time between them.
C. Human insulin is first synthesized as preproinsulin (110 a.a.), then matures into active insulin (A-B domain, 51 a.a.) by releasing a predomain (24 a.a.) and a C domain (31 a.a.). Choose the most appropriate choice for the relative values of the substitution rates of a. pre-domain, b. A-B domain, and c. C-domain.
Question reproduced from IBO 2020, Theoretical Exam 2, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)