CH 9: DNA Replications and Recombination Flashcards
(30 cards)
Conservative, dispersive, semiconservative replication models
conservative - entire double stranded DNA molecule serves as a template, end up with a fully conserved DNA molecule and a new one
dispersive - both strands break into fragments to serve as templates and then reform into two complete DNA molecules containing both old/new fragments
semiconservative - each DNA strand serves as a template for a new DNA molecule
What was Meselson and Shahl’s findings?
E. coli has semiconservative replication
What are replicons?
segments of DNA that undergo replication, includes replication origin
What is theta replication in E. coli? What direction?
replication of circular E. coli DNA, has one origin of replication and two replication fork in a bidirectional replication
circular DNA replication, 2 strands unwind and form replication bubble and replication continues until both replication forks meet
How does linear replication occur in eukaryotic replication?
multiple origins of replication form replication bubbles, DNA synthesis occurs and forks move outwards, forks merge with one another and DNA segments fuse, create two identical linear DNA molecules
Theta vs linear eukaryotic replication
DNA template - circular vs linear
Breaking nucleotide strands - does not occur
Number of replicons - 1 vs many
Uni vs bidirectional - either vs bidirectional (opposite directions on leading lagging strands but still goes 5’-3’)
Products - 2 circular molecules vs two linear molecules
What is required for linear eukaryotic replication (3)?
template strand, nucleotides, enzymes and proteins
What direction does DNA polymerase move?
5’ → 3’
Phosphodiester bonds
link backbone of two adjacent sugars on DNA strand
DNA polymerase only adds nucleotides to the ? end of a growing strand. Replication occurs in ? direction. How is continuous and discontinuous replication present in replication?
3’, 5’ → 3’
leading strand - continuous
lagging strand - discontinuous Okazaki fragments
What is the relationship between direction of replication on leading and lagging strand?
antiparallel on opposite strands
Prokaryotic and eukaryotic cells have what 3 things for replication?
initiator proteins, DNA polymerase, run in 5’ → 3’ direction
What is the initiator protein in E. coli? What is the origin replicon called?
DnaA in E. coli binds to oriC and causes a section of DNA to unwind
oriC is the initiation site for origin replicon
What associated proteins and enzymes are part of unwinding in bacterial cells?
iniator protein - starts unwinding
DNA helicase - breaks hydrogen bonds between bases of two nucleotide strands of a DNA molecule
ssbs - prevent strands from snapping back together
DNA gyrase/ topoisomerase - prevents supercoiling and relieves torsional strain
E. coli and in bacteria requires ? to separate DNA strands before helicase can attach.
initiator
During elongation what is single strand DNA used as?
a template for DNA synthesis
What is primase? What are primers?
primase makes short RNA sequences that are primers
primers are short RNA strands that have a 3’-OH group so DNA polymerase can attach and start adding nucleotides
How are primers utilized in leading and lagging strands?
leading is continuous - one primer needed
lagging is discontinuous - new primer for each Okazaki fragment
What enzyme is elongation carried out by? What are the 5 components to an active replication fork?
DNA polymerase III
- helicase - unzip DNA
- SSBPs - prevent secondary structures
- DNA gyrase - decrease torsional strain
- primase - make primers with 3’-OH group at beginning of each DNA fragment
- DNA pol III - synthesize leading and lagging nucleotide strands
What are the functions of DNA pol I and ligase?
DNA pol I - removes and replaces primers
ligase - zaps gaps when primers are removed and new nucleotides are put in
Exonuclease activity - DNA pol I vs III
exonuclease activity - correcting polymerase errors
DNA pol I - 5’-3’ and 3’-5’ activity
DNA pol III - 3’-5’ activity
DNA pol I - removes and replaces RNA primers with DNA
DNA pol III - elongates DNA
What functions of E. coli’s DNA polymerases have in common?
make complementary seq to template that is antiparallel
use dNTPs to make new DNA
5’-3’ direction adding nucleotides to 3’-OH group
catalyze phosphodiester bond by joining 5’ phosphate group to 3’-OH group of previous nucleotide
works with many proteins
Exonuclease activity engages in proofreading. What direction is proofreading? What enzyme? What is mismatch repair?
3’ - 5’ by DNA polymerase I
enzymes excise incorrect nucleotides and replace them after replication is complete
Termination in different cells, ex. E. coli
some molecules end when replication forks meet
E. coli requires termination protein TUS to bind to Ter site to form a complex
