Question

m-RNA is synthesised on DNA template in which direction

• A. 5' ? 3'
• B. 3' ? 5'
• C. both a and b
• D. any.

Answer 1

The Correct Option is A

The process of synthesizing mRNA on a DNA template is known as transcription. It is a crucial step in gene expression, where the information in a gene is transcribed into messenger RNA (mRNA). Let's explore the directionality involved in this process.

1. Direction of DNA Template: The DNA strand that serves as the template for mRNA synthesis is read in the 3' to 5' direction. This is because DNA polymerases, the enzymes responsible for copying the DNA sequence into RNA, can only add nucleotides to the 3' end of the growing mRNA strand.
2. mRNA Synthesis: As the DNA template is read in the 3' to 5' direction, the mRNA strand is synthesized in the 5' to 3' direction. This is how the newly formed mRNA strand becomes a complementary copy of the DNA template strand, with uracil (U) replacing thymine (T) as is standard in RNA.
3. Correct Option: Considering the above explanation, the correct direction in which mRNA is synthesized on a DNA template is 5' to 3'. Therefore, the correct answer is 5' → 3'.

Conclusion: The polymerase enzyme specifically facilitates nucleotide addition to the 3' end, leading to extension in the 5' to 3' direction on the growing mRNA strand. The other direction, 3' to 5', is incorrect for synthesis directionality. Options "both a and b" and "any" do not apply because the synthesis has a specific and defined direction.