DNA Synthesis Flashcards
What type of replication does DNA undergo?
Semi conservative
What is a replication origin?
The specific site where DNA replication is initiated when
recognised by an initiation complex
What is a replication bubble?
Where the DNA unwinds to allow access to the replication machinery
How many replication origins are there in mammalian
DNA replication strands?
Multiple
How are the bubbles removed from the strands?
Eventually they coalesce and produce 2 daughter
chromosomes
When does DNA synthesis occur?
(Synthesis) Phase S
How long does the mammalian cell cycle last?
16-24 hrs
What are the phases of the mammalian cell cycle
M phase, G1, G2 and S phase
Why is the mammalian cell cycle longer than bacterial?
Mammalian DNA contains many more chromosomes
In bacterial DNA, how many replication origins are there?
one
Which enzyme synthesises new DNA strands?
DNA polymerase
Name the different types of Polymerases used in
bacterial DNA replication and their functions
DNA Polymerase I - repair
DNA Polymerase II - repair
DNA Polymerase II - repair
What are the different polymerases and their functions
in eucaryotes?
ɒ alpha - replication Β beta - replication ɣ gamma - mitochondrion δ delta - causes elongation 𝜺 epsilon - elongation
List the essential features of DNA polymerase
- Acts in a 5’ - 3’ direction
- uses AT and GC base pairing
- Requires a DNA template or primer
- Has proof reading functions
What requirements need to met before replication can begin?
OH on 3C
4 dNTPs
Magnesium ions
What are dNTPs?
Deoxyribonucleoside triphosphates
- Building blocks of DNA
e. g. dATP, dGTP, dCTP, dTTP
How is the sugar phosphate backbone formed?
Hydroxyl group attacks the 1st Phosphate
causes release of pyrophosphate
leaving 1 phosphate to react with the hydroxyl to form the
backbone
Why is one DNA strand formed discontinuously?
DNA polymerases only work in 5’ - 3’ direction
- one strand will be made continuously
the other = discontinuous
Where is a replication fork found?
At the replication origin
What is the lagging strand?
3’ - 5’ strand - DNA pol. works in opposite direction so a
primer has to be laid down over again
What does the reinitiating of replication multiple times form?
Okazaki fragments
Define okazaki fragments
Short newly synthesised DNA strands formed on the lagging strand
What is the role of DNA helicase?
Unwinds double helix
What does topoisomerase do?
Removes coils in the DNA
