5 words
semi conservative
anti parallel
complementary
New DNA from 5’ to 3’
a fork is 1/2 a bubble
What happens at initiation?
- Begins at origin
- DNA gyrase unwinds doube helix
- DNA helicase breaks double strand into single strand forming bubbles
- Single stranded binding proteins attach to the free DNA sections to prevent re-annealing
Where does initiation begin?
Origins: specific points on chromos
- Prokaryotes have 1 per chromosome
- Eukaryotes have multiple which speeds up replication
What unwinds DNA double helix?
DNA Gyrase enzyme
What separates DNA double strand?
DNA helicase breaks H-bonds between bases
What prevents the double helix from reforming during initiation?
SSBP - prevent re-annealing
What happens at elongation?
- RNA primase attaches to parent strand and lays down RNA nucleotide(s) (primer)
- DNA polymerase III attaches to 2 parent strands’ primer and attaches complementary bases from 5’ to 3’
Leading strand
- RNA primase attaches to 3’ end of parent strand and puts down RNA nucleotide
- DNA polymerase III binds to RNA primer and begins adding complementary nucleotides TOWARDS the fork
- When poly 3 reaches the end of the fork, DNA polymerase I dismantles the primer and replaces it with DNA nucleotides
Lagging strand
- RNA primase attaches to parent strand and puts down RNA nucleotides
- DNA polymerase III binds to RNA primers and begins adding complementary nucleotides in 5’ to 3’ direction AWAY the fork
- poly 3 continues until it reaches another primer then detaches
- another RNA primer and poly III attach and add nucleotide upstream to (closer to fork)
- RESULT: discontinuous pieces called OKAZAKI FRAGMENTS
- Poly 1 removes the primers and replaces for DNA nucleotides
- DNA ligase then joins the OKAZAKI fragments with phosphodiester bonds
ORDER OF ENZYMES LEADING
RNA primase
DNA Polymerase III
DNA Polymerase I
ORDER OF ENZYMES LAGGING
RNA primase
DNA Polymerase III
DNA Polymerase I
DNA ligase
What happens during termination?
- DNA automatically goes back to helix
- Lagging strand and leading strand uneven due to RNA primers so it is snipped off
What is a telomere?
- end of chromosome that holds useless info
- buffer loss of DNA which takes place at termination
What happens when telomere gone? what happens telomere regen cant be shut off?
- telomere gone = dead cell
- telomere stays alive forever = cancer cell
Proofreading
- poly II checks to make sure H-bonds between base pairds are present.
- If not, enzyme removes new nucleotide and inserts the right one
Why do we need DNA replication?
Growth, reproduction, repair
