Question

At a specific area of a chromosome, the sequence of nucleotides below is present where the chain opened to form a replication fork:

3' C C T A G G C T G C A A T C C 5'

A 7-nucleotide RNA primer is formed starting at the underlined T (T) of the template. What is the primer sequence, including 5' and 3' end?

The "T" in bold is the underlined T.

Answer 1

In DNA replication, DNA synthesis occurs in 5' to 3' direction . Lagging strand needs to be replicated in the opposite direction of the way the replication fork is proceeding. So in the lagging strand ,where the RNA polymerase synthesize a short RNA primer in 5' to 3' direction, which will be extended by DNA polymerase 111. Primer is RNA strand, so the adenine bases will be replaced with uracil. Later when the lagging strand formation is completed , the RNA primer will be replaced with deoxyribonucleotides by DNA polymerase I . DNA polymerase 1 removes RNA primers and fills the gaps between Okazaki fragments with DNA. DNA ligase then joins the okasaki fragments.

3' C C T A G G C T G C A A T C C 5' is the template strand in replication fork.

The primer will be,   5' A C G U U A G 3'