DNA Replication

Question 1

(check) Describe DNA Replication (leading strand)
Use “BURDEn”

Answer 1

Initiation
”Bubble formation
1. Helicase recognises and binds to A-T rich the origins of replication sequences, forming a *replication bubble** with 2 rep forks.
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Unwinding
2. Helicase uses energy from ATP to unwind double stranded DNA by breaking H bonds btwn comp base pairs
3. Single stranded DNA binding proteins bind to single stranded DNA to prevent the strands from reannealing
4. Topoisomerase
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Elongation
1. Primase synthesises RNA primers via CBP to provide the free 3’OH end needed for DNA pol 3 to bind to and add DNA nucleotides via CBP
2. DNA pol 3 reads temp strand from the 3’ to 5’ direction and adds deoxyribonucleotides in the 5’ to 3’ direction
3. Incoming deoxyribonucleotides CBP with temp strand
4. DNA pol 3 catalyses formation of phosphodiester bonds btwn the 3’OH end of the growing strand and 5’ phosphate end of incoming deoxyribonucleotides
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Termination
1.

Question 2

Lagging strand DNA synthesis

Question 3

Exp how DNA replication results in 2 daughter molecules identical to the parental DNA?

Answer 3

1. Semi-conservative DNA replication occurs and both parental strands separate to act as 2 template strands
2. to synthesise new daughter strands_ via CBP.
3. Each of the resulting DNA molecule consists of 1 parental DNA strand and 1 newly synthesised DNA daughter strand.
4. The newly synthesised DNA molecules have the same seq as the original

Question 4

O Why does the end replication problem arise?

Answer 4

• ## The last RNA primer at the 5’ end of the daughter strand used to synthesise the last Okazaki fragment of the lagging strand would be removed.
• ## But there is no free 3’OH upstream to allow DNA polymerase 1 to add nucleotides and replace the last primer.
• So the extreme 3’ end of parental DNA is unreplicated

Question 5

Why does Euk genome have multiple origins of replication?

Answer 5

Euk genome has a large amt of DNA to be replicated so it needs multiple origins of replication to increase speed of replication