The expression of Gene A is up-regulated (increased) by the activator B, which b

Question

The expression of Gene A is up-regulated (increased) by the activator B, which binds to the enhancer C upstream (before) of Gene A. Activator B is also activated by the effector hormone D. Once the activator B is bound by the effector D, it binds to the enhancer and recruits RNA polymerase, which binds to the promoter of gene A.

a) How many mutations are possible for C that would prevent the gene from turning on?

b) How many mutations are possible for D that would prevent the gene from turning on?

c) How many mutations are possible for RNA polymerase that would prevent the gene from turning on? Do not count a mutation that stops its polymerizing activity.

Explanation / Answer

a) One mutation in ehnacer C will inhibit it from binding to the activator B and hence prevent the gene from turning on.

b)One mutation in effector D will inhibit it from binding to the activator B, so the activator B will not be ativated and hence prevent the gene from turning on.

c) Two possible mutations in RNA polymerase would prevent it from turning on the gene. One mutation that prevents the binding of RNA polymerase to B activator and the other mutation which inhibits the recruitment of RNA polymerase at the promoter region.

d) One possible mutation in the promoter region of the DNA will inhibit the recruitment of RNA polymerase to the promoter thus preventing the gene fron turning on.

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