Question

Consider the following sequence of genomic DNA which is a template strand containing the beginning of the open reading frame for a gene. 3'TAAACTGTACAGGGCCATAACT..5' a) Find the open reading frame and identify the start codon by circling it. b) Transcribe the open reading frame into a strand of mRNA. Identify the start codon by circling it. c) What is the peptide encoded by this strand of mRNA.

Answer 1

According to the base pairing rules, in RNA adenine pairs with uracil (A-U) in RNA, and cytosine pairs with guanine (C-G).

a) It is known that the most common codon is AUG. The start codon is the first codon of mRNA, that's why it contains U. So, a complementary DNA code must be TAC, so it will be transcribed into AUG:
3'TAAACTGTACAGGGCCATAACT5'

b) Starting from the start codon AUG and according to the base pairing rules, mRNA will be transcribed into the following sequence:

DNA: 3'TAAACTGTACAGGGCCATAACT5'
RNA: AUGUCCCGGUAUUGA

c) According to the genetic code chart, the following mRNA sequences will code for the following amino acid sequences:

RNA: AUG UCC CGG UAU UGA
Protein: Met-Ser-Arg-Tyr-

The last codon (UGA) is a stop codon, so it will not be translated. It is a signal for translation termination.