Cell Cycle and DNA Replication Flashcards
In which phase of the cell cycle does DNA replication occur?
S phase
What occurs in the G1 phase of the cell cycle?
Cell content replication (organelles develop)
What occurs in the G2 phase of the cell cycle?
Double check and repair, enzymes and poteins are synthesised
What occurs in the M phase of the cell cycle?
Cell division
What is the order of the cell cycle?
G1, S, G2, M
What are cyclins?
Proteins that control the progression of cells through the cell cycle by activating cyclin-dependent kinase enzymes.
What is DNA Helicase?
An enzyme that unwinds DNA double helix to separate the two parental strands and make them available as template strands.
What is an exonuclease?
An enzyme that cuts nucleotides at the end of the polynucleotide chain
What is an endonuclease?
An enzyme that cuts nucleotides in the middle (not the ends) of the polynucleotide chain
What is the function of DNA Polymerase?
DNA Polymerase is responsible for assembling nucleotides
What is the function of an exonuclease domain in a DNA Polymerase?
Responsible for the recognition and excision of mispaired bases (proofreading mechanism)
How could a mutation in the exonuclease domain of DNA Polymerase cause tumours?
No proofreading would occur so any mispaired bases would not be excised. This would lead to the accumulation of mutations and the formation of a tumour as the DNA becomes more unstable.
Which enzyme joins Okazaki fragments?
DNA ligase
What is stage G0?
G0 stage is a resting stage in which cells do not continue through the cell cycle (eg when nerve/cardiac cells are mature)
What is a replication fork?
This is a Y-shaped region on a replication DNA molecule where new strands are being synthesised
What are Okazaki fragments?
These are short, newly synthesised DNA fragments that are formed on the lagging strand during DNA replication
What are required to initiate DNA replication?
RNA primers
What is the leading strand?
Strand of DNA that is synthesised continuously in the 5’ to 3’ direction
In which direction does DNA polymerase work?
5’ to 3’
What is the lagging strand?
Strand of DNA that is synthesised discontinuously in short Okazaki fragments (away from the replication fork)
Why might there be a problem with producing the final Okazaki fragment on the lagging strand?
This is due to the end replication problem. RNA primer is removed so the DNA at the end is not replicated. This would lead to the DNA getting shorter after every replication.
Consequence - could possibly result in certain genes not being expressed.
What mechanism is in place to overcome the end replication problem?
Telomerase adds repetitive nucleotide sequences to the ends of DNA (telomeres). Therefore, the telomeres get shorter every time, not the DNA.
What is topoisomerase?
Topoisomerase binds to DNA and cuts the phosphate backbone during DNA replication. If left unabated, the torsion would stop the ability of DNA to replicate.
What is non-homologous end joining?
A pathway that repairs double-strand breaks in DNA by joining the two ends of DNA together
What is a potential problem with non-homologous end joining?
If there has been a beak in the DNA, the ends are still joined together but that part of DNA is lost.
What are chromosomal translocations?
A piece of DNA is translocated to another chromosome
What are chromosomal inversions?
A whole gene within the DNA is inverted
