Question

Please help me solve this genetics problem, my professor wasn't able to explain it clearly!! Please give details on how to some this problem.. Thanks

4. Mutation and effects The following protein fragments (amino acid sequences) were found. Wildtype (non-mutated) a. Knowing this information, what nucleotides could encode this protein fragment. Fill in the table using capital letters for nucleotides you know know for certain and lower case letters or the underscore for those you are unsure of -be as specific as possiblehsre net ther A Ga5 b. A mutation altered the Proline (P) amino acid at position 2 to a histidine (H) amino acid. Specifically, what nucleotide was changed and to what other nucleotide in the codon? at other nucleotide in the codon?A

Answer 1

Ans. Given, the amino acid sequence as follow-

M             P              R             C             G

M (one letter code for amino acid) = Methionine (Met- three letter code for amino acid)

P= Proline (Pro), R= Arginine (Arg), C= Cysteine (Cys), G= glycine

Ans. A. the nucleotides sequence (5’3-’) for the given oligopeptide (N -C terminus) is-

M (1)                       P(2)                         R(3)                         C(4)                         G(5)

AUG                        CCU 2a                   CGU 3a                   UGU 4a                   GGU 5a

                                CCC 2b                   CGC 3b                   UGC 4b                   GGC 5b

                                                                CGA 3c                                                   GGA 5c

                                                                CGC 3d                                                   GGG 5d

For example, our nucleotide sequence is- 1- 2b- 3c- 4a- 5d. The sequence can be any possible combinations, but always in series (5’-3’) of 1-2-3-4-5.

Note:

(1) to (5) just indicate the amino acid position in the oligopeptide.

The underscored nucleotides in a group indicates that they can be interchanged without changing the amino acid they encode.

2a and 2b indicate the possible nucleotides for amino acid (2). So, the combination of first two amino acids may be 1- 2a or 1-2b. Similarly, it’s accounted for rest of the nucleotides in any combination along the series (always 5’-3’end).

The limitation of nucleotides for proline aty position 2 is limited to two because only these two nucleotides may encode histidine when mutated.

Ans. B. A mutation leading to change in amino acid from proline to histidine may be due to following changes-

                                Proline     Histidine

                2a            CCU        CAU                        C at 2^nd nucleotide of the Pro codon is changed for A in His codon.

                2b            CCC        CAC