How does semi conservative replication happens?

Answer 1

Semi-conservative replication is a process in DNA replication where each strand of the original double-stranded DNA molecule serves as a template for the synthesis of a new complementary strand. This occurs during the S phase of the cell cycle. Enzymes called DNA polymerases catalyze the addition of nucleotides to the growing DNA strand based on the complementary base pairing rule (A with T, G with C). The end result is two daughter DNA molecules, each consisting of one original parental strand and one newly synthesized strand.

Answer 2

1. Helicase unwinds the DNA strands. The replication fork opens up.

2. Single stranded binding proteins (SSB's) hold the 2 strands apart while replication takes place.

3. Primase synthesizes a RNA primer to which DNA polymerase III can bind.

Primase + proteins = primosome.

4. DNA polymerase III synthesizes the new DNA strand in the 5'------>3' direction.

(Remember, both strands act as templates) DNA poly III + proteins = replisome.

5. The leading strand is synthesized continuously, while the lagging strand is synthesized in fragments called Okazaki fragments. (Fig. 11.12a)

6. As the Okazaki fragments are completed, DNA polymerase I removes the RNA primer and replaces it with DNA.

7. DNA ligase seals the nicks in the sugar-phosphate backbone of the lagging strand.

8. Replication stops when the replisome reaches the termination site (ter) on the DNA.

9. Daughter molecules are intwined (catenanes) - topoisomerases break the strands temporarily so they can separate.