Question

During translation in eukaryotes the anticodon to be aligned with the initiation codon is
(a) 5’ UAC 3’
(b) 3’ UAC 5’
(c) 5’ UCA 3’
(d) 3’ CAU 5’

Answer 1

Hint: The gene expresses itself through the process of transcription and translation in which the DNA part of the gene is used to make mRNA which is then used to make polypeptide chains of amino acids i.e. protein synthesis.

Complete Answer:
A tRNA molecule is responsible for conducting translation by reading the codon sequence present on mRNA using the anticodon loop present in it and bringing the amino acid associated with the codon. Each codon has a specific tRNA molecule as the anticodon loop present in that tRNA has a specific base pair sequence that is complementary to the codon sequence. The codon sequence of the initiation codon is AUG thus the anticodon loop of the tRNA molecule will have the complementary codon which is UAC. The mRNA codon is read in 5’ to 3’ direction thus the direction of anticodon will be 3’ to 5’. Hence the anticodon of the first initiation codon is 3’ UAC 5’.

Additional information: Let us look at the structure of tRNA in detail.
- tRNA was known before the genetic code was postulated and was called sRNA (soluble RNA) .
- A tRNA molecule has an anticodon loop by which it reads the codon sequence on mRNA and it also has an amino acid acceptor end by which it binds to the associated amino acid.
- The secondary structure as in the 2D structure of tRNA looks like a cloverleaf.
- Whereas the actual structure looks like a compact molecule of inverted L.
So, the correct option is (b) 3’ UAC 5’.

Note:
- George Gamow was the first scientist to suggest that codons code for amino acids and they must be present in a combination of three.
- Stop codons do not have any tRNA molecule for them and thus the process of translation stops once we reach the stop codon.
- There are three stop codons with the sequence UAA, UAG, and UGA.