Question

Refer to the table of codons for the following question.

A possible sequence of nucleotides in the template strand of DNA that would code for the polypeptide sequence phe-leu-ile-val would be _____. (Hint: TEMPLATE strand!)

	5’ TTG-CTA-CAG-TAG 3’
	5’ AUG-CTG-CAG-TAT 3’
	3’ AAA-AAT-ATA-ACA 5’
	3’ AAA-GAA-TAA-CAA 5’

Answer 1

Here, the correct option is 3' AAA GAA TAA CAA 5'

Explanation -

We have the amino acid sequence of the polypeptide chain i.e., PHE - LEU - ILE - VAL

The translation is the process in which the polypeptide chain is synthesized with mRNA as a template. The tRNA and ribosomes assist this process. The mRNA consists of the nitrogenous base sequence which acts as the template. A codon is a three-base group in the mRNA which is used in the translation process. These codons are used as a recognition site for the anticodons to bind to them and the tRNA (where the anticodons are already located on the other side) release the one corresponding amino acid (located on that tRNA molecule) to the growing polypeptide chain. This process goes on and a polypeptide chain is produced.

The three-letter codons are the base sequence and the code for a particular amino acid. It may possible that two or more codons codes for the same amino acid because we have 64 possible codons and only 20 amino acids.

So, the codons for the amino acids given are:

PHE: UUU, UUC

LEU: CUU, CUC, CUA, CUG

ILE: AUA, AUC, AUU

VAL: GUG, GUC, GUU, GUA

Now, Transcription is the process by which an RNA sequence is synthesised using DNA as a template. During transcription, the template strand of DNA acts as the template and mRNA is synthesised based on this template. This reaction is catalysed by DNA dependent RNA polymerase. The RNA sequence formed is complementary (adenine to uracil, thymine to adenine, guanine to cytosine and cytosine to guanine) to the template strand of DNA.

But, according to the question given the sequence of the mRNA will be

5' UUU CUU AUU GUU 3'

And the template strand DNA sequence will be: 3' AAA GAA TAA CAA 5'

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