lecture 11 Flashcards
having more than one replication origin can
speed up reactions
conservative model
completely new strand
parental strand remains the same
how many replication forks at each origin?
two replication forks are formed at each replication origin
How does the replication fork move?
DNA replication is bidirectional (each fork moves in opposite directions)
Dynamic movement— changes as replication occurs
Raw materials needed for DNA replication (5)
-DNA template
-deoxyribonucleoside triphosphates (dNTPs)
-a protein complex involving the DNA polymerase enzyme
-DNA/RNA primer
-Mg^2+ ions (cofactor)
polymerization starts from the —- end
5’ to 3’ end
(the complementary strand– NOT the template strand)
DNA polymerase (enzyme) function
proofreading; checks for mistakes in nucleotide sequence during replication
–> cuts them and correct base pair is added
catalyzes the addition of nucleotide 3’ end of a growing nucleic acid
corrects its own mistakes
what does DNA polymerase require in order to function
requires an existing 3’ end to function (can’t begin a new strand otherwise)
exonuclease function
degrade nucleic acids from the end
endonuclease function
cleave nucleic acids within a sequence
–> works like a backspace on a keyboard
DNA polymerase corrects errors using a —- exonuclease (during proofreading)
3’ to 5’
4 contributing factors to the accuracy of DNA polymerase
- H bonding of complementary base pairs
- DNA polymerase monitors the base-pairing before catalyzing the addition of the nucleotide
- cells maintain roughly equal concentration of dNTPs
- proofreading
DNA polymerization sites
separate site for DNA polymerization (P) and error correcting (E)
how does the E site work>
the incorrect nucleotide is pushed to site E when there is an error
can DNA synthesize a new strand without a primer?
NO!!!
primase proofreading ability?
Primase does not have a proofreading ability— but doesn’t matter bc primer will be removed anyways
primase definition
an RNA polymerase that creates RNA primers using a DNA template
how does primase work?
-how many does leading/lagging need?
adds nucleotides 5’ to 3’ (the strand being synthesized).
leading strand only needs one primer.
lagging strand needs many primers.
Replication machine requires
coordination of several proteins
DNA ligase
links the primers together!!!
-seals the gap between the two okazaki fragments during replication
-requires ATP
-happens during DNA repair phase
3 proteins that the replication machine requires coordination of (and their function)
- DNA helicase= pries the double stranded helix apart, requires ATP hydrolysis
- Single-stranded DNA binding proteins= bind to a single stranded DNA, prevents them from reforming base pairs
- DNA topoisomerases=relieves tension that builds up in the replicationm fork, creates nicks in the DNA
sliding clamp keeps
DNA attached to DNA
clamp loader locks
new clamps onto the DNA
2 problems with primers
- RNA primers are replaced w DNA except for the primers used at the very 5’ end of the newly synthesized strands
–> not replaced bc DNA polymerase needs an nuc that already exists to add incoming dNTPs - the single stranded part can’t be filled in! vulnerable to degredation. DNA may get shorter and shorter each time
What is the solution to the 2 primer problems?
telomerase!!!
telomeres attract enzymes (telomerase) which extend the length of the telomeres using an anti-internal RNA template
Models of replication
Semiconservative
Dispersive
Conservative
Semiconservative model
each daughter molecule has one parental
Dispersive model
daughter molecules have patches of old and new DNA
Conservative model
one completely new strand. parental strand remains the same/intact
replication origins are rich in–?
opened up by –?
rich in A-Ts
opened up by initiator proteins (including helicase, SSB –single stranded binding proteins and topoisomerases)
