Carey, pages 1189 - 1191 :
Problems 28.14 - 22
1. Sickle cell anemia is a genetic defect in the structure of hemoglobin,
in which just one amino acid is altered. One glutamic acid is replaced by
a valine. Describe why this change could be so serious for the protein tertiary
structure.
Suggest a possible code in the DNA that might have been altered
in order to read Val instead of Glu.
The Glu residue in hemoglobin carries a negative charge
and may be important for interacting with a positive charge somewhere or
just for making that part of the molecule water-soluble.
A change to Val makes that residue nonpolar. It may be
that the Val residue avoids water or the other polar environment where
Glu was normally found, and this causes the drastic conformational change
in tertiary structure that leads to sickle-shaped red cells.
The m-RNA codons for Glu are GAA and GAG.
The m-RNA codons for Val are GUX (where X can be any of
the four bases).
The most likely error is that a GUA or GUG was accidentally read instead of
GAA or GAG. In both cases, U appears in the second base where A should have
been.
2. Some codons can be deduced from simple homopolynucleic acids, e.g.,
poly-A. Explain.
Identify the four amino acid codes that can be deduced this
way.
Poly-A would produce only Lys.
Poly-C would produce only Pro.
Poly-G would produce only Gly.
Poly-U would produce only Phe.
