Although DNA polymerases require both a template and a primer, the following DNA was found to serve as a substrate for DNA polymerase in vitro in the absence of any additional DNA or RNA. Explain how this could happen and give the sequence of the product of this reaction. Note: dNTPs and DNA polymerase are supplied but no primase is around in this in vitro DNA synthesis reaction.
3'-TGAGCCCATAGCCGTGGGCTCAACCGTAGACCACGAATAGCA-5'
3'- TAGCCG ACCGTAGACCACGAATAGCA-5'
The blue region and the yellow region of this DNA are complementary to each other, thus the blue region can fold back to hybridize with the yellow region. The 3'-end of the blue region can be used as a primer (hence no need for primase) and be extended following a standard DNA synthesis process.
Compare and contrast E. coli polymerase I and III?
see diagram
Explain why the two replicating DNA strands are labeled "leading" and "lagging"
Because DNA synthesis has to follow the 5' to 3' direction, new DNA synthesis using one of the templates (ssDNA) can start right away (leading strand) while the DNA synthesis on the complementary template has to wait for while until enough room on the template is generated (lagging strand). The following diagram highlights the difference:
