Question

The nucleotide sequence on the antisense strand of DNA which is transcribed as codon that specifies the amino acid serine is
(a) TCA
(b) AGU
(c) TAC
(d) CCC

Answer 1

Hint: Genetic code is an equivalence between sequence of amino acids in polypeptide and nucleotide sequence in DNA. The genetic code is in the form of triplets which consist of three nucleotide bases and represent 64 codons for 20 amino acids.

Complete answer:
The code which represents serine is UCU, UCC, UCA, UCG, AGU, and AGC. In transcription, the synthesis of RNA takes place from DNA. Only one strand of DNA functions as a template for RNA synthesis which is called an antisense strand. From the given option TCA code for AGU, AGU code for UCA, TAC code for AUG, and CCC code for GGG in which only AGU code represents serine.

Additional Information: Genetic code has certain characteristics, like-
It does not show overlapping in three successive nucleotides. It does not possess punctuation. It is a specific and unambiguous code for only one amino acid. The same codon specifies the same amino acid in all organisms. AUG and GUG represent the start codon. The code reads in 5 to 3 directions, which code for mRNA. Addition, deletion, and replacement of codon result in a change of reading of genetic code. Amino acids with similar properties specified by related codons and also genes take part in the synthesis of a single polypeptide, and the number of cistrons equal to the number of polypeptides.
So, the correct answer is ‘TCA’.

Note: UAA is ochre, UAG is amber and UGA is the opal, all this codon is a stop codon which does not code for any amino acids and terminates the translation process of polypeptide synthesis. These codons are also called degenerate codons as it provides resilience against point mutation.