Question

Shown below are the amino acid sequences of the wild-type and three mutant forms of a short protein. Each mutation results from a single nucleotide change (transition/transversion / insertion / deletion). Use this information to answer the following questions. Hint: First, reconstruct as much as you can of the wild-type RNA sequence and then reference that sequence when analyzing the mutations. Wild type: met - gin-ala - ser-val - arg - phe Mutant 1: met - gln - pro-ser - val - arg - phe Mutant 2: met - arg-leu-val -ser-ala -leu Mutant 3: met - gin-ala - ser-val - cys - phe a. Using the genetic code table in your text, predict the type of mutation that occurred leading to each altered protein and describe the mutation thoroughly. Example: Mutant X: gly to trp; missense, GGG to UGG; transversion (G to U), 1“ position, 9 codon. b. Analysis of the mutations allows you to reconstruct a great deal of RNA sequence of the original, wild-type allele. Write down as much of the wild-type sequence as you can. For nucleotides that are still unknown, draw a blank line, (e.g. CC_).

Answer 1

Wild type sequence :

met - gln - ala - ser - val - arg - phe

AUG - CAG - GCU - UCU - GUU - CGU - UUU

a1) Mutant 1 - proline instead of alanine which means - CCU instead of GCU . So here C is replaced by G. So this mutation is termed as transversion.

2) Mutant 2 - met - arg - leu - val - ser - ala - leu
There is absence of two amino acids and presence of the new amino acids. leu present twice which has the genetic code of UUA or UUG. Gln is deleted. So there is deletion. Leu is added so there is insertion.

3) Mutant 3 - met - gln- ala - ser - val - cys - phe
Here there is replacement of arg with cys. Arg has the genetic code of CGU whereas cys has UGU. SO here there is transition mutation. Because there is conversion of pyrimidine to pyrimidine.