Genomes I - Lecture 7 Flashcards
What is a genome?
The complete set if DNA molecules possessed by an organism
How many DNA molecules are in the human genome?
24
How many chromosomes are in a human diploid cell?
46
Where does DNA replication in E.coli start?
○ Begins at the origin of replication - always the same position on the genome
○ Two replication forks - bidirectional
Where does DNA replication in human DNA start?
○ Begins at the origin of replication - many on each chromosomal DNA molecules
○ Not always at the same site
○ Each replication fork copies about 150kb of DNA
○ Replication starts at different times
How is E.coli DNA replication initiated?
○ DnaA proteins bind close to the origin of replication
○ DNA becomes wound round these proteins
○ Forces base pairs to break at the origin of replication - origin is A-T rich
What is the prepriming complex?
○ Formed by attachment of DnaB protein to the origin
○ DnaB is a helicase
○ DnaB breaks more base pairs so the replication forks move away from the origin
What is the primosome?
○ Formed by attachment of two primase enzymes
○ These make the RNA primers that initiate replication of the two leading strands
What is the gamma complex?
○ In E.coli
○ Attaches and detaches Pol III from the lagging strand
What is the beta complex?
○ In E.coli
○ Holds Pol III onto template allowing it to slide
What is PCNA?
○ Proliferating cell nuclear antigen found in humans
○ Sliding clamp that holds DNA pol delta tightly onto DNA
How does the replications forks in E.coli always meet at the same point?
There are terminator sequences and each one is a binding site for a Tus protein and they are directional
What are Tus proteins?
○ Allow the replication fork to pass in one direction but not the other
○ Permissive face: replication fork can pass through
○ Non-permissive face: replication fork is blocked
○ Multiple are needed to stop replication
How are replication forks controlled in human DNA?
Forks just merge
