DNA replication, enzymes at replication fork & DNA replication accuracy Flashcards
What is a chromosome?
nuclear genetic material distributed along chromsomes
What are telomeres?
areas of highly repetitive DNA
protect chromosome ends from degradation, recombination & end fusion
what is a centromere?
repetitive DNA
forms spindle attachment in mitosis
What is the origin of replication?
sequence where duplication of DNA begins
has many
what is semi-conservative replication?
discovered by Mehselton & Stahl
centrifugation with different isotopes of N and bacteria
each generation had half light and half heavy N
settle at different points in the test tube
What is involved in DNA synthesis?
DNA polymerase
Mg2+
Single stranded template of DNA
Primer 3’-OH
Synthesis in 3’ to 5’ direction
differences between eukaryotic and bacterial genomes
euk are large & arranged as linear chromosome
bact are small, compact and circular
what is the replication fork?
the site here both strands of DNA are copied at
in 5’ to 3’ direction
leading strand is continuous
lagging strand is discontinuous
what are the discontinuous fragments called?
Okazaki fragments
What are the steps in lagging strand synthesis?
- Primase synthesises RNA primer
- DNA polymerases elongate primer with new DNA
- Nucleases removed RNA at 5’ end of neighbouring fragment
- DNA polymerase fills the gap
- DNA ligase connects adjacent Okazaki fragments
What are the different enzymes present at the replication fork?
helicase - unwinds DNA
ss-binding protein - stabilises DNA
primase (RNA polymerase) - synthesises RNA primer
DNA polymerase- creates new DNA strand & proof read
Sliding clamp - keeps DNA polymerase on DNA
clamp loader - loads clamp onto DNA
nuclease - trim Okz fragments
DNA ligase - joints Okz fragments
What is primase?
specialised RNA polymerase that creates RNA primers
what is the speed of DNA replication?
50 base pairs s-1 at each fork
high as DNA polymerase attaches to sliding clamp
What is a sliding clamp?
keeps DNA polymerase on the DNA
loaded on by DNA clamp loader
What are the steps of clamp loading?
- Loader binds to clamp
- Opens the clamp
- DNA then engages in clamp
- ATP hydrolysis locks the clamp round the DNA by closing it
- Release of clamp loader
- DNA polymerase then binds to sliding clamp
- Clamp loader can then be used again