In sickle-cell anaemia the sixth codon of the gene for the beta chain of haemoglobin changes from…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
In sickle-cell anaemia the sixth codon of the gene for the beta chain of haemoglobin changes from GAG, for glutamic acid, to GUG, for valine. A student lists every change of one base in the codon GAG. There are 9 such changes, 3 for each of the 3 places.
- How many of them are silent?
- How many are missense?
- How many are nonsense?
- Which kind is the change from GAG to GUG?
Need a reminder? The key ideaShow
A codon has three bases. Of the 64 codons, 61 code for amino acids and 3 are stop codons, and AUG is the start codon. A point mutation can be silent, missense or nonsense. An insertion or a deletion of 1 or 2 bases shifts the reading frame, and an insertion or a deletion of 3 bases keeps it.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. The codon GAG for Glu.
Plan. Make the 9 codons and use the table.
Step 1. The first base. CAG is Gln, AAG is Lys, and UAG is a stop codon.
Step 2. The second base. GCG is Ala, GGG is Gly, and GUG is Val.
Step 3. The third base. GAU and GAC are Asp, and GAA is Glu.
Step 4. (a), (b) and (c). Silent: GAA, . Nonsense: UAG, . Missense: the other .
Step 5. (d) GUG codes for valine, a different amino acid. It is a missense mutation.
Answer: ; ; ; missense.
Check. changes.
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