2023 Molecular Basis of InheritanceTranscription – Coding Strand and Template Strand Medium Question 32 of 200 in Molecular Basis of Inheritance

Which one of the following is the sequence on corresponding coding strand, if the sequence on mRNA formed is as follows: $5'$-AUCGAUCGAUCGAUCGAUCGAUCGAUCG-$3'$?

A $3'$-ATCGATCGATCGTCGATCGATCGATCG-$5'$
B $5'$-UAGCUAGCUAGCUAGCUAGCUAGCUAGC-$3'$
C $3'$-UAGCUAGCUAGCUAGCUAGCUAGCUAGC-$5'$
D $5'$-ATCGATCGATCGATCGATCGATCGATCG-$3'$

The answer is D.

Solution

The coding strand has the same sequence as the mRNA (T in place of U) and the same 5'→3' polarity.

The two strands have opposite polarity and the DNA-dependent RNA polymerase also catalyses the polymerisation in only one direction, i.e., $5'\rightarrow3'$. The strand that has the polarity $3'\rightarrow5'$ acts as a template, and is also referred to as template strand. The other strand which has polarity ($5'\rightarrow3'$) and the sequence same as RNA (except thymine at the place of uracil), is displaced during transcription. This strand is referred to as coding strand.

Concept sequence of coding strand from mRNA

Molecular Basis of Inheritance in past papers

200 questions from this chapter have appeared across 27 exam years.