DNA Replication

Question 1

Describe the “most beautiful experiment in biology”

Answer 1

The Meselson-Stahl Experiment demonstrated that DNA replication occurs via a semi-conservative mechanism.

Question 2

Describe the models of DNA replication in terms of DNA polarity.

Answer 2

All known DNA polymerases extend DNA from 5’ to 3’. However, the strands are antiparallel. DNA is replicated in a semi-discontinuous manner, meaning it is continuous on the leading strand (towards the replication fork) and discontinuous on the lagging strand (away from the replication fork).

Question 3

How does replication priming occur?

Answer 3

RNA polymerases can synthesize RNA de novo. DNA polymerases require either a DNA or RNA primer for subsequent extension.

Question 4

How were Okazaki fragments discovered?

Answer 4

1. Tsuneko and Reiji Okazaki added T4 bacteriophage to E. coli.
2. ³H-thymidine was used to label newly synthesized DNA.
3. DNA was extracted at various times.
4. Alkaline sucrose gradient centrifugation was used to demonstrate the existence of small DNA fragments and their incorporation into longer lengths of DNA.