Cell Cycle Flashcards
What does mitosis result in
2 genetically identical diploid daughter cells
What does meiosis I result in? Meiosis II?
Meiosis I - two genetically different haploid cells
Meiosis II - 4 haploid cells - two identical pairs
What does crossing over occur?
Prophase I
Re-assortment of genetic material between homologous or paired chromosomes
What are the phases of cell cycle
G1 - gap after mitosis of cell from previous cycle and before DNA synethsis
S - DNA synthesis
G2 - gap between completion of DNA synthesis and start of cell division
M - mitosis - cell division
(G0) - non dividing cells such as corneal endothelium, neurones remain in resting noncycling state
What controls progression through cell cycle?
Cyclins
Cyclin dependent kinases stimulate cell cycle progression by phosphoylating specific proteins in the cell required for transiion to the next stage
What is the restriction point in G1
Once passed the cell is committed to completing its cell division
What occurs at the G1-S checkpoint?
Ensures that previous cycle of division has been completed and any resultant damage repaired
What gene acts at the G1-S checkpoint
p53 gene - tumour suppressor gene - restricts entry of cells with damaged DNA to the S phase - regulates passage of cell through the restriction point
What happens at the G2-M chekpoint
Ensures that dNA synthesis and resultant damage are repaired before mitosis occurs
What arethe phases of mitosis
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis
What happens in prophase?
Cells chromatin condenses
Chromosomes become visible as a pair of sister chromatids - joined at centromere
Centrioles duplicate and migrate towards opposite poles of cell
Spindle of microtubules is formed - nucleoli disperse
Prometaphase in mitosis
Breakdown of nuclear envelope
Formation of kinetochores - attachment point between chromosomes and the spindle at the centromere
Metaphase (mitosis)
Chromosomes attach to the spindle by the kinetochore and line up to form equatorial plate
Anaphase (mitosis)
Centromeres separate and the chromatids and pulled to opposite poles by spindle
Clustering of complete set of chromosomes at each pole of the cell
Telophase (mitosis)
Chromosomes begin to uncoil again
Nuclear membrane reforms
Nucleoli reappear
Cytokinesis (mitosis)
Cleavage forms in middle of cell dividing in two
Prophase 1 (meisois)
Homologous chromosomes come together and cross over, exchange segments in homologous recombination
Process of prophase 1 (meiosis)
Leptopene - spindle forms
Zygotene - chromosomes shorten, thicken
Pachytene - chiasmata form - crossing over
Diplotene - exchange of genetic material between homologous chromosomes
Diakinesis - recombinant chromosome formed
Metaphase 1 (meiosis)
Chromosomes attach to the spindle
Anaphase 1 (meiosis)
Whole chromosomes migrate to opposite poles)
Telophase 1 (meiosis)
2 genetically different haploid cells are formed
What happens in meiosis 2
In anaphase II - sister chromatids separate rater than chormosomes - forming 2 identical pairs of haploid cells (4 cells altogether)
What processes generate genetic diversity?
Chiasmata formation from corssoing over in prophase I - random exhage of genetic material between homologous chromosomes
Independent segregation of homologous chromosomes occurs during anaphase I
How many combinations possible in gamaets
2^23 combinations
What is formed in meiosis of oocytes?
One definitive oocyte
One secondary oocyte
One polar body
What is apoptosis?
Cell death that is programmed
After intra or extracellular physiological triggers during development/remodelling, defence, homeostasis, ageing
Pyknosis - condensation of nucleus
Karyorrhexis - nucles fragments)
Cells shrink
Organelles maintain structure
Cell membrane forms irregular buds
Cells break into smaller bodes
Phagocytosed by macrophages
What is pyknosis?
Condensation and fragmentation of chromatin
Condenses into patches against the nuclear envelope as a result of endonuclease activity
What is karyorrhexis?
Nuclear envelope becomes discontinuous and DNA fragments
What induces p53? What does it do
Tumour suppressor gene
Induced by DNA damage
TRanscription factor results in arrest of cell cycle in G1 to allow DNA repair
What does Hcl-2 do
Suppresses some apoptotic pathways
rEduction in levels of Bcl-2 associated with apoptosis
What are telomeres?
Repetitive DNA sequences found at the end of chromosomes
Synthesised by telomerase - no replicated in the same way as other chromosomal DNA
How is apoptosis initiated?
Direct result of TNF production by macrophage
Fas ligand binds Fas receptor - formation of death inducing signalling complex (DISC) - contains FAS assocatied protein with Death Domain (FADD), caspase-8 and caspase-10
Sequence of events triggers apoptosis
