→ GAG (glutamic acid) GAG First →GTG Exact (glutamic acid) mutation (valine) reversion First →GTG Equivalent (glutamic acid) mutation (valine) reversion GAG > GAA (glutamic acid) Equivalent > GAT (aspartic acid) GAG First →GTG (glutamic acid) mutation (valine) reversion

Biochemistry
9th Edition
ISBN:9781319114671
Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Chapter1: Biochemistry: An Evolving Science
Section: Chapter Questions
Problem 1P
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A reversion is a mutation that returns a mutant codon back to a
codon that gives a wild-type phenotype. At the DNA level, this type
of mutation can be an exact reversion or an equivalent reversion.


An equivalent reversion produces a protein that is equivalent to the
wild-type protein in structure and function. This outcome can
occur in two ways. In some cases, the reversion produces the
wild-type amino acid (in this case, glutamic acid), but it uses a
different codon than the wild-type gene. Alternatively, an equivalent
reversion may substitute an amino acid structurally similar
to the wild-type amino acid. In our example, an equivalent reversion
has changed valine to an aspartic acid. Because aspartic and
glutamic acids are structurally similar—they are acidic amino
acids—this type of reversion can restore wild-type structure and
function.
Here is the question: The template strand within the coding
sequence of a gene has the following sequence:
3′–TACCCCTTCGACCCCGGA–5′
This template produces the following mRNA:
5′–AUGGGGAAGCUGGGGCCA–3′
The mRNA encodes a polypeptide with the following sequence:
methionine–glycine–lysine–leucine–glycine–proline
A mutation changes the template strand to this sequence:
3′–TACCCCTACGACCCCGGA–5′
After the first mutation, another mutation occurs to change this
sequence again. Is each of the following second mutations an exact
reversion, an equivalent reversion, or neither?
A. 3′–TACCCCTCCGACCCCGGA–5′
B. 3′–TACCCCTTGACCCCGGA–5′
C. 3′–TACCCCGACGACCCCGGA–5′

→ GAG
(glutamic acid)
GAG
First →GTG
Exact
(glutamic acid) mutation (valine) reversion
First →GTG Equivalent
(glutamic acid) mutation (valine) reversion
GAG
> GAA
(glutamic acid)
Equivalent > GAT
(aspartic acid)
GAG
First →GTG
(glutamic acid) mutation (valine) reversion
Transcribed Image Text:→ GAG (glutamic acid) GAG First →GTG Exact (glutamic acid) mutation (valine) reversion First →GTG Equivalent (glutamic acid) mutation (valine) reversion GAG > GAA (glutamic acid) Equivalent > GAT (aspartic acid) GAG First →GTG (glutamic acid) mutation (valine) reversion
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