Cell cycle Flashcards
How do we study the cell cycle? (Experimental)
Info about cell cycle in complex eukaryotes gained from genetic study of simple eukaryotes (e.g. yeast)
Simple eukaryotes - more prominent haplophase than humans
Identify cell cycle protein factors: frog eggs, marine invertebrates
How do we visualise the cell cycle?
Fuse proteins w/ fluorescent markers
Phases of cell cycle
(1) Interphase: G1, S, G2 (+ G0 = terminally differentiate)
(2) Mitotic phase
G1 phase (interphase)
First growth phase
Longer than other phases
Growth, produce proteins/enzymes/organelles for protein synthesis
Centromeres form
Cells differentiate and perform specialised functions as part of whole tissue (cells start to differentiate before leaving cell cycle)
S phase (interphase)
Nuclear DNA replicated
G2 phase (interphase)
Second growth phase Nuclear envelope forms around nucleus Check for replication errors Cont. cell growth in prep for division Centromeres contain centrioles
G0 phase
Terminal differentiation, leave cell cycle
Mitosis
Distribute (duplicated) chromosomes equally between 2 potential daughter cells
- Prophase (mitosis)
Chromosomes visible in nucleus Condense, shorten Nucleolus disappear Centrioles migrate to opp poles Microtubules form spindle fibres
- Prometaphase (mitosis)
Nuclear envelope dissolves
Mitotic spindle move to nuclear area
Chromosomes attach to spindle at kinetochores
- Metaphase (mitosis)
Chromosomes move to spindle equator (metaphase plate)
Kinetochore ensures anaphase not begin until all chromatid pairs aligned at equator = metaphase checkpoint
- Anaphase (mitosis)
Split centromeres Astral microtubules (join centriole to cell cortex under plasma membrane) Sister chromatids pulled to opp poles of cell = exact division duplicated genetic material
- Telophase (mitosis)
Chromosomes uncoil
Nuclear envelope reassemble
Nucleolus reforms
Cytokinesis
Cell division = 2 identical daughter cells
Position of cytoplasmic division defined by spindle equator
Plasma membrane indented = cleavage furrow
Constricts cell until division
Cell cycle control
Cyclin-dependent protein kinases
Controls HIGHLY CONSERVED during eukaryotic evolution
Lose control = tumourigenesis
Cell cycle checkpoints
Monitor cell cycle progress
Loss = genome instability and disease
Check: DNA fully replicated, not damaged, chromosomes attached to spindle (metaphase checkpoint)
Delay DNA replication or cont. cell cycle
Ensure chromosome no. correct, mitosis complete
Cancer
Deregulation of cell cycle
Defects in checkpoints: repair proteins not assemble properly, no cell cycle response to DNA break signal
Meiosis
Produce gametes w/ haploid no. chromosomes
Genetic diversity
Meiosis I
Reduction division
Follows normal S phase in primary gametocytes (DNA duplicated)
Prophase I (meiosis)
Chromatids cross over - exchange genetic info between homologous pairs = chiasma formation
Mix maternal and paternal alleles
Metaphase I + Anaphase I (meiosis)
Maternal and paternal homologous pairs separate at random
Seperation via microtubule spindle
First meiotic division = 2 daughter cells w/ 1 chromosome of each pair
New combos of maternal/paternal genes on chromosomes
Meiosis II
Follow meiosis I
No intervening S phase
4 gametes produced
Metaphase II (meiosis)
Split chromatids by divide centromeres
Anaphase II + Telophase II (meiosis)
Chromatids migrate to opp poles
Second meiotic division
Generation of variation (meiosis)
Crossing over (prophase I) Independent assortment of maternal and paternal homologs (meiosis I)
Genetic linkage
Genes loci close on same chromosome = less likely separate via recombination, LINKED
Gametes w/ parental genotype more common than recombinants, more likely co-inherited
Ataxia-telangiectasia (clinical)
Rare autosomal recessive
Clinical features: Cerebella ataxia (death purkinje fibres) = poor control movement, dilation blood vessels, T-cell immunodeficiency, predisposition to lymphomas and leukemias
Mutations in genes encode ATM protein kinase - acts at DNA damage checkpoint, cell cycle cont. when chromosomes broken
