During transcription the DNA strand with 3'→5' polarity of the structural gene always acts as a template because
- Nucleotides of DNA strand with 5'→3' are transferred to mRNA.
- Enzyme DNA dependent RNA polymerase always catalyse the polymerisation in 5'→3' direction.
- Enzyme DNA dependent RNA polymerase always catalyse the polymerisation in 3'→5' direction.
- Enzyme DNA dependent RNA polymerase always catalyse polymerisation in both the directions.
The Correct Option is B
Approach Solution - 1
- During transcription, the DNA strand with a 3' → 5' polarity serves as the template for RNA synthesis.
- The RNA polymerase synthesizes the mRNA in the 5' → 3' direction by reading the DNA template strand in the 3' → 5' direction.
- The RNA polymerase catalyzes the addition of nucleotides to the growing mRNA strand, which occurs in the 5' → 3' direction, while it reads the template in the opposite direction (3' → 5').
The correct answer is (B) : Enzyme DNA dependent RNA polymerase always catalyse the polymerisation in 5'→3' direction.
Approach Solution -2
The correct answer is: (B) Enzyme DNA dependent RNA polymerase always catalyzes the polymerization in 5'→3' direction.
During transcription, one of the DNA strands is used as a template for the synthesis of messenger RNA (mRNA). The strand that has the 3'→5' polarity of the structural gene always acts as the template strand. This is because the enzyme responsible for RNA synthesis, DNA-dependent RNA polymerase, catalyzes the polymerization of RNA in the 5'→3' direction.
RNA polymerase moves along the DNA template strand in the 3'→5' direction, which allows the RNA strand to be synthesized in the 5'→3' direction. This is due to the antiparallel nature of the DNA strands. The RNA molecule is complementary to the template DNA strand, and since RNA polymerase adds nucleotides to the growing RNA chain in the 5'→3' direction, it must read the DNA template strand in the 3'→5' direction.
Therefore, the correct explanation is that RNA polymerase catalyzes the polymerization in the 5'→3' direction, and hence the template strand must have the 3'→5' polarity for proper mRNA synthesis.
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