Identify the sequence of bases of m-RNA molecule synthesised on the given strand of DNA AGCGATTAC.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → UCGCUAAUG
During transcription, mRNA is built on a DNA strand by complementary base pairing. In DNA, adenine pairs with thymine and guanine with cytosine. RNA has uracil (U) in place of thymine, so an adenine of DNA pairs with uracil in the mRNA:
DNA A → RNA U, DNA T → RNA A, DNA G → RNA C, DNA C → RNA G
Applying this base by base to the given strand:
DNA: A G C G A T T A C
mRNA: U C G C U A A U G
So the mRNA is UCGCUAAUG.
Why the other options are incorrect
Option (1) ACGCATTAG — Incorrect. It contains T, which RNA does not have, and its first base A is not complementary to the A of DNA.
Option (2) TGGCTAATG — Incorrect. This keeps thymine and is a DNA-type sequence; it is also not complementary at the second base (G opposite G).
Option (4) UCGCUTTUC — Incorrect. The first five bases are right, but it then copies T T opposite T T of DNA instead of pairing them with A A, and RNA has no thymine.
NCERT (2026-27 edition):
Chemical Composition of Nucleic Acids – “… DNA contains four bases viz. adenine (A), guanine (G), cytosine (C) and thymine (T). RNA also contains four bases, the first three bases are same as in DNA but the fourth one is uracil (U).”