PL section - DNA replication Flashcards
Which gene is one of the most well stored in DNA?
ribosomal gene
(importance of protein synthesis)
How is DNA information stored from kept from cell to cell?
by DNA replication
What are 3 necessary things for DNA replication?
- Primer sequence (DNA pol can’t start new strand, can only elongate)
- Pool of unincorporated nucleotides
- Proteins that collaborate to catalyse
What reaction starts the addition of a new nucleotide to the DNA chain?
- Matching in the base pairs between template and incoming dNTP
- Polymerization (3’ OH attacks alpha-phosphate of incoming dNTP)
What is the replication fork?
Area where nucleotides are added, where DNA parent duplex separate
Replication fork moves along the double helix as replication occurs
What is the role of DNA helicase in the DNA replication?
Allows parent DNA duplex strands to separate
What is a Primer?
Primer = Short RNA molecule complementary to single-stranded region of DNA parent
(Because DNA pol cannot initiate synthesis of a new strand)
What is Primase?
It an enzyme, a specialized RNA polymerase which forms a NEW complementary RNA molecule which will be elongated for DNA replication
What are the Leading and Lagging strands?
Leading strand = side where new strand in synthesized continuously from 5’ to 3’ (adding on 3’ end, which is at the replication fork)
Lagging strand: replication fork is at 5’ end so not continuous synthesis
Okazaki fragments are synthesized with multiple short RNA primers (starting at replication fork and going to next RNA primer)
What are Okazaki segments?
Short discontinuous fragments consisting of RNA and DNA
What is the role of DNA ligase?
It joins 2 Okazaki segments (after RNA primer was replaced by DNA)
What is the replisome?
The molecular machine involved in DNA replication
On what organisms were discovered much of what we know about DNA replication?
Prokaryotes (ex: E. coli)
Viruses (SV40) bc viruses attack host and uses the host’s mechanisms so easier to study them
What is the large T-antigen ?
It is a protein encoded by SV40 genome (the only one)
Hexamer = 6 subunits (2x3 copies of the same)
It s a helicase
Role = unwinds double helix at replication fork
What is the role of RPA?
Binds single-stranded + keeps it single-stranded DNA template in optimal conformation for DNA pol:
1. incorrect base pairing = higher energy (incorrect base=pairing is only 50x less favorable)
2. makes DNA pol move faster
3. keeps geometry of proteins s.t. wrong protein can’t access and form incorrect base pairing (error rate = 1/10,000 instead of 1/50)
Important for accuracy of DNA replication
What is the role of DNA Polymerase Epsilon?
Elongates leading strand by DNA synthesis
What is the role of PCNA protein in DNA replication?
Proliferating Cell Nuclear Antigen
It is a homotrimeric protein (forms a ring around template)
It prevents the Pol epsilon and delta complex from dissociating from the template
Forms a collar around DNA strands which also helps speed up replication
What are the roles of primase and of DNA polymerase alpha?
Primase forms RNA component of the primer
DNA polymerase alpha recongnizes RNA primer and extends primer with DNA
What is the role of the Replication Factor C (RFC) protein in DNA replication?
It is the PNCA loader, opens up the PCNA ring and loads it at a primer on DNA
What are the roles of Ribonuclease H and FEN-1 in DNA replication?
Ribonuclease H and FEN-1 displace (eats up) the RNA component at the 5’ ends of the Okazaki segment