VPB 321: Animal Biotechnology (2+1)

DNA REPLICATION

• DNA replication is to copy their strands. Each strand of original strand act as template to copy the information to synthesize the new strands. It is a fundamental process of all living organisms.

Steps in DNA replication

1. Separation of the two parental strands is the starting point of DNA replication.
2. Separation of strands happens in places of the chains which are rich in A-T.
3. Helicase is the enzyme that separates the two strands.
4. The initiation point where the separation starts is called "origin of replication".
5. The structure that is created is known as "Replication Fork".
6. Once the DNA strands separated, then, RNA Primase binds in the the initiation point of the 3'-5' parent chain. RNA Primase can attract RNA nucleotides which bind to the DNA nucleotides of the 3'-5' strand due to the hydrogen bonds between the bases. RNA nucleotides are the primers (starters) for the binding of DNA nucleotides.
7. The elongation process is different for the 5'-3' and 3'-5' template.
8. 5'-3' Template: The 3'-5' proceeding daughter strand -that uses a 5'-3' template- is called leading strand because DNA Polymerase can "read" the template and continuously adds nucleotides.
9. 3'-5'Template: The 3'-5' template cannot be "read" by DNA Polymerase. The replication of this template is complicated and the new strand is called lagging strand. In the lagging strand the RNA Primase adds more RNA Primers. DNA polymerase reads the template and lengthens. The gap between two RNA primers is called "Okazaki Fragments".
10. In the lagging strand the DNA Pol I -exonuclease- reads the fragments and removes the RNA Primers. The gaps are closed with the action of DNA Polymerase (adds complementary nucleotides to the gaps) and DNA Ligase (adds phosphate in the remaining gaps of the phosphate - sugar backbone).