Which precursor molecule would serve as the substrate that formed the first nucleotide in segment E if adenine is the first base on thee template strand corresponding to the initiation point for segment E?
The correct answer to this question is option C – DTTP From the image above, we can see a replication fork. This clearly states that the on-going process is DNA replication and not RNA transcription. DNA replication is a semiconservative process that occurs in 5’ to 3 ‘direction. It involves both leading and lagging strands.
The leading strands start from 5’ direction, and the lagging strand faces the 3’ direction. If adenine is the first nucleoside triphosphate molecule added on the 5’ end, then the precursor molecule that would serve as the substrate that formed the first nucleotide in segment E is DTTP (deoxythymidine triphosphate). Options A and B are wrong because uracil is not a nucleotide present in DNA. Therefore, it cannot be the substrate formed. Only triphosphate nucleosides are added in DNA replication, making other options wrong.