Question

Please answer the following questions about primers:

a) Explain how the primers are made for the Sanger sequencing when we even don't know the sequence of the DNA yet ?

b) Do all cells in the body have the same primer and starting site for the DNA polymerase ? Do all primers have an idetical base sequence ? Is the same set of primers used for both leading and lagging strands ?

c) Are primers made of DNA or RNA ?

Answer 1

1) There are many methods by which the primers for unknown DNA sequence can be made:

An adaptor DNA with known sequence can be added to our DNA and corresponding primer can be synthesized. This can be used to start replication of unknown sequence

Secondly, by using a vector. Here similarly to the last method, the unknown DNA is inserted into a know vector or plasmid. As we know the plasmid sequence, we can replicate the DNA sequence using a primer for plasmid known sequence. Hence this is also called universal primer. But its benigit is that here you can also find the sequence from the reverse direction and can be helpful for very long sequences

2) All the cells in a body has the same DNA sequence as it was formed by mitosis in the gestational period. So every cell has the same primer for same sequence. But in a cell there are many genes and hence many primers for replicating different DNA sequence. So the different primer will have different base sequence a/c to the DNA sequence. But all will have same DNA polymerase.

Well the sequence of leading and lagging strands are complimentary and but the same. So different primers will be required. As a fact many different primers will be required in lagging strand to synthisise the okazaki fragments.

3)The primers can be boyh DNA & RNA, but RNA primer is most commonly use in sanger sequencer.