Lectures 3 + 4 (AT) Flashcards
(29 cards)
Give a brief outline of what happens at each stage of the cell cycle.
G1 - cells grows and develops.
S - DNA is replicated.
G2 - the cell now has twice the amount of DNA. Ready for cell division.
Give a brief outline of what happens at each of the checkpoints of the cell cycle.
G1/S - the size and condition of the DNA is checked. If damaged in anyway, or if the cell is too small, the process is halted.
G2/M - the condition of the DNA is checked again.
M - the formation of the metaphase plate is analysed.
What is a kinetochore?
The structure responsible for the movement of chromatids to the opposite poles of the cell as the spindle fibre retracts.
What happens during…
A. Interphase
The chromosomes are extended and uncoiled, forming chromatin.
B. Prophase
The chromatin condenses to form distinguishable pairs of chromatids that are attached by a centromere. The centrioles replicate and begin to migrate to the opposite poles of the cell.
C. Prometaphase
The nuclear envelope disintegrates and the chromatids begin to associate with the MTs of the spindle.
D. Metaphase
The chromatids align on the equator and associate with the MTs via their centromeres and the kinetochores.
E. Anaphase
The spindle fibres contract. The sister chromatids migrate to the opposite poles of the cell.
F. Telophase
The nuclear envelope begins to reform and the cytoplasm divides.
Name the three types if MTs.
Astral, interpolar and kinetochore.
How was the S phase promoting factor hypothosised?
Cell fusion experiments. Two cells containing nuclei in different stages were fused. The S phase nucleus was dominant over G1 but not G2. It was proposed that an S phase promoting factor was acting, and that is has an effect on G1 but not G2.
What is the effect of the mitosis promoting factor?
Dominant over all interphase nuclei.
Explain the experiments of Yoshio Masui and the Xenopus frogs.
Xenupos eggs arrest at 2 key stages - they arrest at metaphase II when the eggs are laid, and G2 when thet are an oocyte in the ovary. To determine what was holding them back, the cytoplasm of an egg arrested at metaphase II was injected into an oocyte arrested at G2. Initiated maturation process –> MPF hypothesised.
What did Tim Hunt discover?
Cyclins.
Importance of cyclins?
Cyclins are being synthesised continuously, but are destroyed periodically. Their levels peak before and after cell division. Levels dip during. Their destruction reflects the loss of MPF activity during the metaphase to anaphase transition.
What type of yeast did Lee Hartwell work with?
Saccharomyces cerevisiae, budding yeast.
What type of yeast did Paul Nurse work with?
Schizosaccharomyces pombe, fission yeast.
What did Nurse discover? How?
cdc2 –> cell division control 2 (cdk1).
Nurse used temperature sensitive mutants and transformed them with a cDNA library of a whole genome. Most mutated yeast could not grow in restrictive conditions. In some rare cases, the transformed yeast cells could grow due to their transformation with the WT copy of the mutated gene. The cDNA was isolated and the protein predicted.
MPF is a complex of…
Cdc2, cdc13 and cyclin B.
CDK and cyclin(s) associated with G1/S checkpoint?
CDK 4/6 and Cyclin D.
CDK and cyclin(s) associated with S checkpoint?
CDK 2 and Cyclins E/A.
CDK and cyclin(s) associated with G2/M checkpoint?
CDK 1 and Cyclins A/B.
Explain the M phase checkpoint in terms of MPF.
MPF destruction is what governs the metaphase –> anaphase transition. MPF destruction is prevented until the chromosomes have aligned on the equator.
Explain the G1 & S phase checkpoints in terms of the ‘restriction point’.
Both upstream and downstream of R there are different cyclin complexes that control entry into the S phase.
UPSTREAM: Cyclin D in G1.
DOWNSTREAM: Cyclin E,A in S.
