Question

21. List the ways that a new virus can suddenly appear on the world stage and how climate change or habitat destruction may impact where/when viruses appear. 22. Here it is. Fully describe the process of DNA replication including all the proteins involved in that process and their functions.

Answer 1

Answer 22

DNA replication does not start at random locations but at particular sites, called origin of replication. Unit of DNA in which replication starts from an origin and proceeds bidirectionally or umidirectionally to terminus is called a replicon. Replicon could be linear or circular. Prokaryotic replicon are generally circular.

here we use dna replication of E.coli (Prokaryote) to understand it.

The genome of E.Coli is replicated bidirectionally from a single origin called oriC.

Proteins involved in dna replication ;

1. Proteins involved in initiation of replication - DnaA, Single stranded DNA binding proteins(SSb), DnaB (Helicase), DnaC and DnaG(Primase).

2. Proteins required for chain elongation and connecting the okazaki fragments - DNA Polymerase, SSb, DNA Gyrase and DNA ligase.

3. To relieve the positive supercoiling before the replication fork - DNA gyrase.

4. Proteins for termination of replication & segregation of daughter molecules - Terminus binding proteins (Tus), DNA topoisomerase IV. :

DNA polymerase requires single stranded DNA as template. Thus, Helicase opens up the duplex at replication fork to provide single stranded template. The primary helicase (DnaB) binds to and move along the lagging strand template in 5' to 3' direction unwinding the duplex.

Single stranded binding proteins inhibits the reannealing of separated strands.

Primase synthesizes a short RNA primers to prime the DNA chain elongation.

Topoisomerases are required to relieve the positive supercoiling that arises from DNA unwinding mediated by helicase.

In prokaryotes (E.Coli) it is generally fulfilled by DNA gyrase.

DNA polymerase catalyzes the synthesis of DNA. DNA polymerase III is the primary enzyme involved in the DNA replication. It is multiprotein complex that consists of distinct polupeptides - etc.

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