DNA replication Flashcards
(7 cards)
1
Q
When does DNA replication occur?
A
It occurs during interphase just before mitosis to make DNA copy before dividing
2
Q
What is semiconservative replication
A
Definition: The process of DNA making a copy of itself before cell division
Outcome: The new DNA molecule will end up with one parent strand and one daughter strand (newly created)
3
Q
Steps of semiconservative replication
A
1: Strand separation
2: Building complementary strands
3: Proof reading and repair
4
Q
Step 1: Strand separation
A
Step 1 is a 5 step process
- Origin of replication: Replication begins in an A-T rich area because A-T only has two bonds
- Helicase: An enzyme that unwinds the double helix by breaking the H bonds between base pairs
- Replication fork: As the helicase works, it separates the two strands and creates a replication fork and replication bubble
- Single Strand Binding Proteins (SSBs): prevents single strands from rejoining each other
- Topoisomerase: releases tension from DNA unwinding
5
Q
Step 2:
A
6
Q
Step 2: Building complementary strands
A
Step 2 is an 5 step process
- Primase: makes RNA primer at 3 prime end of parent strand
- DNA Polymerase III: Binds to RNA primer and adds nucleotides in the 5 prime 3 prime direction (moves along the parent strand in the 3’ to 5’ direction, but forms the new strand in the 5 to 3 direction)
- Leading and lagging strand: the leading strand on the replication fork is continuously being built towards the helicase (only one RNA primer is needed on this side of the fork). And the lagging strand is built in chunks called Okazaki fragments, away from the helicase (requires many RNA primers)
- DNA Polymerase I: Comes in and removes RNA primers and replaces them with DNA nucleotides
- DNA Ligase: seals the gaps in the Okazaki fragments by forming phosphodiester bonds
7
Q
Step 3: Proofreading and repairs
A
Step 3 is an 4 step process
- DNA polymerase I and III proofread: As these enzymes work they check for mistakes, removing and replacing if any
- Nucleases cut out damaged or incorrect nucleotides: if there is an damaged or mistaken nucleotide, an enzyme called nucleases will cut it out
- DNA polymerase fills in gaps: After nucleases cut out DNA, DNA polymerase will fill in the gaps with new/correct nucleotide
- DNA ligase: An enzyme called DNA ligase will seal any remaining gaps to make strand continuous again
