Unit 3 - Replication and repair Flashcards
Conservation Model
- parental DNA would make TWO NEW DNA strands
-the new daughter strand would joing to from one double helix and the original parent DNA remain as its start DH
Semi - Conservative model
- TWO NEW DAUGHTER strand were replicated would bind to a parent strand to form a double helix
- this each DNA mol of first replication would contain a parental strand
Dispersive Model
-Parental strand broke into SMALL FRAGMENTS
-at end each small fragment bind to pieces of newly copied DNA completing DH
-each one contains PARENTAL FRGAMENTS and newly synthesized fragments
DNA replication process (3)
1) produces two identical copies of the chromosome during S phase
2) catalyzed by my enzymes including: DNA, polymers, helicase, ligase, and primase
3) replication takes place at point where the DNA DH sperates called the replication fork
Initiation of DNA Replication
a portion of the DNA double helix unwinds to expose the bases for new pairing
Elongation of DNA Replication
2 new strands of DNA r assembles using parental DNA as a template
Termination Phase of DNA Replication
the DNA replication process is completed and the 2 new DNA mols sperate
Organization of DNA
in order to fit within a cells nucleus DNA is packed tightly coiled structures called chromatin which unravel prior to replication
Initiation Phase in-depth
- before DNA replication can begin the double helix structure of DNA mol must be unwound from each other
Helicase (initiation phase)
breaks the hydrogen bonds that holds complete nitrogenous bases of DNA together.
Point of separation (initiation phase)
creates a ‘y’ shape called a replication fork and the 2 parent DNA strands now act as templates for making new strands of DNA
Replication origin
the starting point for replication
separating the DNA has challenges
1) tension from unravelling DH can lead to twist and tangle
solution ; topoisomerase
2) annealing strands have a tendency to rejoin or anneal
solution ; ssbs
Topoisomerase
the enzyme that relieves tension caused by the unwinding of parent DNA; they cleave DNA strands, allows the strand(s) to untwist
Single Strand binding proteins
(SSBs) r enzymes that bind to the separated strands to prevent rents DNA strands from them coming back together
Direction to DNA replication
towards direction or replication for on one strand and away on the other ( 5’ to 3’)
in eukaryotes more then one replication fork
this may exist on a DNA mol as a reuslt when two replications fork r near a replication bubble is made
replication bubbles
a the separation of DNA in both directions during replication
Elongation Phase
- DNA polymerase 3 builds a new complementary DNA strand by + new nucleotides
- use nucleoside triphosphate as building blocks
RNA Primase
lays down RNA primers (10-60 RNA bases) to be used by DNA polymerase as a taring point for the new strands
DNA Polymerase 3
- adds complementary bases (a-t and c-g)
- always needs a template strand
- uses RNA primers as a starting point
Job of DNA polymerase 3
they proofread or check their work removing the vast majority of wrong nucleotides that r accidentally added to the chain
Nucleoside Triphosphate
is a ml containing a nitrogenous base bound to a 5c sugar w 2 phosphate groups bound to the sugar
Leading strand
is the DNA strand that is copied continuously in the direction towards the replication fork
- quickly
- 5’ to 3’
Lagging strand
is the DNA strand that is copied away from the replication for
- 5’ to 3’
- much slower process
DNA polymerase 3 (lagging strand)
adds nucleotides from primers to primer making Okazaki fragments
Okazaki fragments
is a series of RNA primers and short DNA fragments on lagging stand
DNA polymerase 1
replaces RNA primers w appropriate Deoxyribonucleotides. but a gap if left between fragments
DNA Ligase
joins fragments by creating phosphodiester bonds
Termination Phase
eventually two replication forks will fuse together and make a continuous strand of newly synthesized DNA
Termination Phase: DNA polymerase enzymes carry out replication proofreading correcting errors
-most often base pairs mismatches; DNA polymerase 3 cannot go forward if base pair r mismatched. usually back up replaces the incorrect base pair w the correct one
Termination Phase: rare occasions
(1 error for every 1 million base pairs) a mismatched base pair error is present after replication is complete
Termination Phase: special DNA repair…
they repair mechanisms which include DNA polymerase 1 and DNA polymerase 2 read the strand for errors.
Termination Phase: DNA polymerase 2
is a slow enzyme and often works to repair damage to DNA that occurs between replication events
during lagging synthesis, ligase joins together multiple Okazaki fragments (t or f)
T
in DNA replication which of the following events happens during both leading and lagging strand synthesis
RAN primers helps initiate DNA synthesis
