Mitosis and Meiosis Flashcards
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
What is the role of M cyclins?
Activate cdks that stimulate entry into G2/M checkpoint
Mechansisms destroy them later on
What can activate cdk-cyclin complex and how?
Wee1kinase
It phosphorylates the active sites
Which enzyme inhibits the cdk-cyclin complex?
Cdc25 phosphatase
What is APC?
Anaphase promoting complex - ubiquitin ligase
With E1 and E2 it transfers ubiquitin on to M cyclin for its degredation
When is APC activated?
In mitosis by association with Cdc20
What happens in meiosis 1?
Crossing -over and segregation
What happens in meiotic prophase 1?
Homologues pair up
Pairing is faciliated by the synaptonemal complex as well as DNA base pairing between homologues
What is the purpose of homologous recombination between two non sister chromatids?
It aligns the chromosomes up ready for anaphase and facilitates formation of the synaptomenal complex
It allows for genetic recombination between paternal and maternal DNA on the same chromosomes
What percentage of mammalian eggs and sperm are aneuploid?
20%
4%
What is meant by aneuploid?
Cell with an extra chromosome
List four ways proliferation can be detected
1) DAPI is a dye that shows all nuclei
2) BrDU is a thymidine analogue which can detect fluorescent antibodies
3) Pulse treatment can tell you which cells were in S phases during the treatment
4) DNA dyes can be used to sort cells in suspension based upon the fluorescence
