Lecture 1 (AT) Flashcards
(17 cards)
What is the initiator protein that performs replication in bacteria called?
DnaA
What is the initiator protein that performs replication in Eukaryotas called?
ORC (Origin Replication Complex).
What does the replication model suggest?
That there is a sequence of DNA called the replicator to which the initiator protein binds, e.g. in E.coli the replicator is OriC, the protein DnaA.
What does the DUE consist of?
It is A-T rich.
What does ORC consist of?
Made of 6 subunits. ORC-1, 2 & 4 are involved in binding the ACS sequence of S. cerevisiae.
How does the replication model in S.cerevisiae differ to that in S.pombe?
The ORC does not bind to a sequence motif in S. pombe, but A-rich DNA.
ssDNA stabilisation
B: SSB (Single Stranded Binding) protein.
E: RPA (Replicator Protein A).
RNA primer synthesis
B: DnaG
E: Primeosome.
DNAP
B: DNAP III
E: Multiple polymerases are involved.
Sliding clamp
B: Beta clamp, loaded by the gamma factor.
E: PCNA.
What does the Pre-replication complex consist of?
The origin recognition protein (DnaA or ORC), the helicase loader (DnaC or CDT1), and the helicase (DnaB or MCM).
Mutations in the Pre-RC cause what?
The Meier- Gorlin Syndrome.
In bacteria the genome is circular. What determines whether the replication forks (of the bidirectional bubble) meet?
The Tus-Ter system. Ter are sequences of DNA, and when Tus proteins are bound this forms a barrier that can trap the replication fork.
What solutions are available to overcome the problem of simultaneous replication and transcription in bacterial genomes?
- The helicase that travels with the replication fork can push back any blockages.
- The helicase can completely remove the blockages.
- If the RNAP is stalled then the transcript can be cut and transcription reset.
Role of topoisomerases?
Get bacteria back to its relaxed state. Can resolve supercoiling and separate linked chromosomes.
Problem 1 of replicating linear genomes.
Need to replicate every base only once. There are multiple points of origin so this is difficult: if not enough fire then we have under-replication; if the same origin fires multiple times then we have over-replication.
Problem 2 of replicating linear genomes.
At the lagging strand, once RNA primers are removed and the Okazaki fragments are ligased together, this leaves a 3’ overhang. RNA template used by telomerase.
