Lecture 17 and 18 Flashcards
In which direction are nucleotides added to the growing DNA strand?
5’-3’
What enzyme catalyses DNA replication?
DNA polymerase
In what direction does DNA replication occur?
It is bi-directional
Where does DNA synthesis occur?
Replication origins
How does the double helix open up?
With aid of initiator proteins
How big are replication origins in bacteria?
Around 100 bp
How fast do bacterial replication forks move? How long does this take?
500-100nucleotides/sec
30 minutes
How fast is eukaryotic replication fork?
50 to 100 nts/sec
What protein helps opens the DNA helix?
DNA helicase
What does DNA helicase consist of?
6 identical subunits
Why doesn’t the lagging strand fold back on its self?
Single-strand DNA binding proteins (helix destabilizing proteins)
What should the fidelity of 5’-3’ polymerisation be? What is it really?
1 error in 10^5 nucleotides
1 error in 10^7 nucleotides
What are the two proofreading mechanisms used by DNA polymerase?
Monitoring, exonucleolytic proofreading
How does polymerase start replication?
DNA primase doesn’t need base paired end, use ribonucleodie triphosphate to synthesis RNA primers
At what intervals are DNA primase (RNA polymerase) made in eukaryotes?
100-200 nucleotides
What enzyme joins okazaki fragments?
DNA ligase
What enzyme degrades RNA primers?
A nuclease
What enzyme replaces the RNA with DNA?
Repair DNA polymerase
What holds DNA polymerase in place?
Sliding clamp
What is the sliding clamp in eukaryotes?
Proliferating nuclear cell antigen (PCNA)
What does the sliding clamp do?
Improve prossesivity of DNA polymerase
What binds the sliding clamp?
Clamp loader
What enzyme relieves tension and prevents supercoiling?
DNA topoisomerases
What topoisomerase I do?
Produces a transient single-strand break
What does topoisomerase II do?
Transient double strand break in entangled helices
How are the ends of chromosomes replicated?
Telomerase (reverse transcriptase) is a ribonucleo-protein
How do cells distinguish between ends of chromosomes and double-strand DNA breaks?
T-loops
How many errors are there after mismatch repair?
1 in 10^3
0-3 mutations
What 2 proteins are involved in mismatch repair?
MutS and MutL
What is depurination
removes a purine base from a nucleotide
Deaminanation of adenine makes
Hypoxanthine
Deamination of Guanine makes
Xanthine
In what 2 ways is DNA damage removed?
Base excision repair
Nucleotide excision repair
What enzymes remove the sugar phosphate in base excision repair?
AP endonuclease and phosphodiesterase
