Mitosis and Meiosis
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What are the stages of the cell cycle?
G phase 1 Synthesis G phase 2 Mitosis
What are the stages of mitosis?
Prophase Prometaphase Metaphase Anaphase Telophase
What happens in prophase?
Replicated chromosomes condense Mitotic spindle assembles between the two centrosomes which have been replicated and moved apart
What happens in Prometaphase?
Starts abruptly with the breakdown of the nuclear envelope Chromosomes attach to the spindle via the kinetochore
What happens in Metaphase?
Chromosomes are aligned in the middle along the equator The kinetochore microtubules attach sister chromatids to opposite ends of the cell
What happens in Anaphase?
Sister chromatids are synchronously separated They are pulles separate slowly as microtubules get shorter and spindle poles move apart
What happens in Telophase?
Chromosomes decondense at the two poles of the spindle New nuclear envelope reassembles forming two new nuclei
What happens in cytokinesis?
The cytoplasm is divided into two by a contractile ring of actin and myosin filamets, creating two new daughter cells
What are the two types of yeast cell division?
Fission yeast (Schizosaccharomyces pombe) Budding yeast (Saccharomyces cerevisiae)
What are the advantages of using yeast to study cell division?
Rapid division rate (<1 hour) Cell cycle genes are highly conserved Yeast can be grown as haploids or diploids
How can you study which genes are essential for survival?
Genetic tricks allow us to identify lethal mutations: Diploids can be used to maintain lethal mutations that are then studied in haploids Temperature sensitive mutations allow growth only at a permissive temerature
What are the genes called that control cell division?
Cell division cycle genes (cdc genes)
What are the advantages of using the Xenopus as a model for the cell cycle?
Easy to collect eggs Rapid division rate (30 mins) Large size makes purification of proteins easier Can be manipulated by injection of RNAs or chemicals into the oocyte
What is cell free mitosis?
Gentle centrifugation is used to break open a large batch of frog eggs and separate the cytoplasm from other cell components Sperm nuclei is added with ATP The sperm nuclei condense and undergo repeated mitosis
How long does a free mitotic spindle last?
40 to 60 minutes
Where are there check points in the cell cycle?
G1 G2/M Metaphase to Anaphase
What is checked at the G1 checkpoint?
If enviroment is favourable for the cell to commit to the cell cycle and chromosome duplication
What is checked at the G2/M checkpoint?
All DNA is replicated and the enviroment is favourable
What is checked at the Metaphase to Anaphase checkpoint?
Checks that all chromosomes are attached to the spindle
What are cyclins?
Proteins expressed at different levels in the cell cycle They bind to and activate cdks
What is the role of cdks?
They phosphorylate many proteins that are specific to a certain stage in the cell cycle
What are the three classes of cyclins which bind to cdks in eukaryotes?
G1/S cyclins S cyclins M cyclins
What is the role of G1/S cyclins?
Activate cdks in late G1 so help trigger progression through START = cell cycle commitment
What is the role of S cyclins?
Binds to cdks after start and help stimulate chromosome duplication - levels are elavated until mitosis