Lect 3 Flashcards
(30 cards)
Central dogma DNA to…to..
DNA
RNA protein
Importance of replication
Providing genetic info needed by daughter cells
Doubling cells content before division during S phase
Replication process is
Semi conservative
DNA polymerase is… Enzyme
Function
Steps
Template directed
Catalyse formation of polypeptide chain by adding nucleotides from dNTPs
- H bond , base complementation
- Pyrophosphate removal
- Formation of phosphodiester bond
DNA pol synthesis vs read
Requires
5’ to 3’
3’ to 5’
RNA primer with free 3’ OH
DNA ligase func
Requires
Joins 2 DNA segments by catalyzing the formation of phosphodiester bonds
NAD + prokaryotes
ATP eukaryotes
DNA helicase func
Requires
Unwinds the double helix of DNA
ATP
During DNA strand unwinding…occurs which requires….
Supercoiling
Topoisomerase enzyme
Topoisomerase types comparison
1, cuts a nick in 1 strand only allowing rotation and bond reformation afterwards
2, transient break in both strands then reseals the bond, needs ATP, can introduce -ve supercoils
Gyrase
In E.coli can
Introduce -ve supercoils
Separate interlocked DNA molecules after replication
inhibitors
Quinolones> like tarivid and ciprobay, antibiotic inhibits DNA gyrase
Teniposide and doxorubicin> antitumor drug inhibits type 2 topoisomerase
Replication fork
Prepriming complex componenets
V shape and bidirectional
DNA a and DNA B and DNA c bindi g to the ORI c and SSB
Ori C is rich in …why
A–T bonds as only 2 hydrogen bonds present so easier to break
Dna A
Dna B
Dna C
SSB
Produces local opening and unwinding of DNA double helix at Ori C requiring ATP
Also a type of helicase that req ATP
Binds to Ori C
Single strand binding proteins, stabilise single strands and protect from nucleases action
Replication fork is created by the action of…. and…
Helicase
SSB proteins
How SSB proteins bind
Their absence
Cooperatively one molecule makes it easier for the rest
Rewinding of DNA again
Initiation phase
Both strands act as…
RNA primer is….bp formed by…reads from and synthesis
Adds nucleotides from
Primase and prepriming complex form…
Template
5
Primase enzyme, DNA dependent RNA polymerase
3’ to 5’
5’ to 3’
NTPs (ATP/GTP/UTP/CTP)
Primosome
Steps of primase action
- 2 NTPS form H bonds with first 2 nucleotides of template strand
- Loss of pyrophosphate
- Formation of phosphodiester bond
- 3’OH is free as primase moves to 5’ end and another nucleotide is added
Why DNA polymerase do not initiate synthesis of DNA
How start
As the proofreading of the first few nucleotides is not accurate
Adds to 3’OH
Elongation by…
Synthesises …adds nucleotides….from…
DNA polymerase III
Both strands
One at a time
dNTPs
Rate of chain elongation is…..per second
It is highly…….synthesising…… In one cycle
20-50
Processive
50000
The number of nucleotides added to the Nascent chain before the polymerase disengages from the templates
Processivity
The 2 newly synthesised strands grow….
One leading
The other lagging
In opposite directions
one continuously towards and one discontinuously away from the replication fork
Lagging strand formed in pieces abt…….to…called…
1000-2000
Okazaki fragments
