Question

Suppose you add fluorescent ribonucleotides to a cell undergoing DNA replication so that the RNA primers used in DNA synthesis glow when viewed with a fluorescent microscope. You notice that, near each replication fork, one strand glows more than the other. Which strand glows more, and why?

Answer 1

The question is incomplete as it does not have the option which are:

A. The lagging strand glows more because its RNA primer is nearer the replication fork.

B. The leading strand glows more because it is elongated nearest the replication fork.

C. The lagging strand glows more because it forms the "trombone loop."

D. The leading strand glows more because it forms the "trombone loop."

Answer:

A. The lagging strand glows more because its RNA primer is nearer the replication fork.

Explanation:

The process of DNA replication requires the primase enzyme which synthesises RNA primers from the DNA strand. The RNA primers bind to the site near the replication fork from where the replication begins.

If the ribonucleotides are radioactively labelled then the strand which glows brighter than the other will be the lagging strand as the lagging strand is synthesized by the template DNA running in 5' to 3' direction as a result of which the RNA primer moves towards the replication fork.

Thus, Option-A is correct.