Cell Cycle And Meiosis Flashcards
What is another word for mitosis
Somatic cell division (non reproductive)
How many phases does the cell cycle have and name them
4
M phase
G1
S
G2
Explain all 5 stages of M phase (mitosis to cytokinesis)
Prophase - mitotic spindles form from centrosomes
Chromosomes condense
Prometaphase -
Nuclear membrane breaks down
Sister chromatids have formed
Kinetichore microtubules attach
Metaphase-
Chromosomes align on equator
Kinetochore microtubules contract
Centrosomes are at spindle poles
Anaphase -
Split sister chromatids move to spindle poles
Microtubules shorten
Telophase -
Nuclear envelope reassembles around sets
Contractile rings start to contract
Cytokinesis -
Contractile rings (with actin) contract and create cleavage (split cells)
Chromosomes become deconstructed again
Microtubules form again at centrosomes
What is another word for centromere on chromatids which binds to microtubules
Kinetochore
What are contractile rings and function
They contract and actin is involved
This cleaves the cell and split cells in mitosis
Explain the 3 phases briefly of interphase
G1- prepare cell for dna synthesis
Doubles the organelles
Synthesise proteins for dna replication
S- dna replication
G2- prepare cell for mitosis
Synthesise proteins for mitosis
Where are the main checkpoints
G1 + G2
Name the signals/ regulation of checkpoints that show cell is either ready or not
Growth factor proteins
Density optimal of the cell (whether cell is next to others)
Anchorage dependency - cells need to be anchored to others for division
What do the check points look out for in G1 G2 and M phase
G1- whether cell is big enough
If environment is favoured
If dna is damaged (would stop replication)
G2- check dna is replicated and correct
Check environment is favoured
M phase- check all chromatids attached to spindle
Explain the enzyme involved in check points
Cyclin dependant kinase
If cell is ready, the enzyme phosphorylates a protein
This signals to cell to proceed with cell cycle
Why doesn’t cyclin dependant kinase signal to cell on its own
It needs cyclin to activate it
What is quiescence
A pause in cell cycle
Without signal such as Anchorage cells dont proliferate
They enter G0 stage (no growth), they can then reenter G1 of apoptosis
What does frequency of cell division depend on
How long cell is in G0 or G1 phase
And varies in cell types
How do growth factors signal /stimulate cell growth
They will bind to receptor which sends signal for cell to divide
If aren’t present the cell goes to G0
What happens in apoptosis to the cell (programmed cell death)
Cell shrinks
Nucleus breaks down
Membrane forms blebs
Organelles in blebs
This then divide and makes several bodies- organelles still function (recycled)
What happens in necrosis (accidental cell death Eg cell is injured)
Cell swells
Membrane leaks
Nucleus swells
This means immune cells move to it= causes inflammation
Give examples of when apoptosis is triggered
If cell is infected- cytotoxic T cells kill it
Embryonic development - remove tissues
If dna is damaged
Explain the cycle of how p53 growth factor (tumour suppressor) can cause apoptosis cell death
A signal such as dna damage is sent to p53
P53 activation causes mitochondria membrane to rupture
Cytochrome c is released
Activates cascade of caspases(enzymes)
Caspases activate DNAase
Cleaves dna and lamins in nucleus
Causes nuclear fragmentation /cleaved cytoskeleton
Cell detaches from other cells and dies
Explain number of chromatids /sister chromatids through each stage of meiosis
Start with 92 sister chromatids (46 pairs)
Then division causes 46 sister chromatids (23 pairs)
Divide again into 23 chromosomes when uncondensed
What happens in meiosis interphase
Maternal chromosomes will replicate into sister chromatids
Paternal will also replicate into sister chromatids
= 46 pairs (23 pairs from each parent)
What is the synaptonemal complex
Where homologous pairs are drawn together (synapsis) by axial cores (axes) and transverse filaments
What is the synaptonemal complex important for
Crossing over or homologous pair
Explain the 5 stages of prophase
Leptonene - sister chromatids condense
Zygotene - the homologous pairs form through the synaptonemal complex
Pachytene- crossing over takes place
Diplotene - synaptonemal complex disappears and chiasma is present
Diakinesis - pair are bivalent ready for metaphase
Why are the homologous pairs referred to as tetrad
4 chromatids
Explain briefly how crossing over takes place
A specialised protein breaks both strands on 1 of the chromosomes
This then enables branch migration and forms recombinant homologs
What is the spindle equator also called
Metaphase plate
What is removed in anaphase 1between the pairs
Cohesion which kept the pair together removed in disjunction
Describe the development of male gametes starting from primary spermatocyte
The PS undergoes meiosis 1 and forms 2 secondary spermatocytes
Each SS undergoes meiosis 2 and forms 2 spermatids each
Each spermatid then differentiates into a spermatozoa (spermatogenesis)
Explain how a female ovum is developed from a primary oocyte
Primary oocyte divides in meiosis 1 into 1 secondary oocyte and the first polar body
In second division the secondary oocyte divides into an ootid and a second polar body
The ootid then develops into an ovum (1 is produced)
How is female meiosis different
In females meiosis starts at birth and stops after the prophase then at ovulation completed into the secondary oocyte
Only after fertilisation the second division (creating ovum) takes place
When do males gametes start to divide my meiosis spermatogenesis
After puberty
Non disjunction of chromosomes during meiosis produces 2 types of gametes/cells. Name them
Aneuploidy - missing chromosomes (monosomic cells)
Trisomy- added chromosomes (trisomic cells )
What 2 effects can p53 have on cell division
Either stops cell division eg due to dna damage kinases activating p53 to inactivate cyclin dependant kinase
Or by cell apoptosis completely - via caspases and endonucleases
