Cell cycle

Question 1

How do we study the cell cycle? (Experimental)

Answer 1

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

Question 2

How do we visualise the cell cycle?

Answer 2

Fuse proteins w/ fluorescent markers

Question 3

Phases of cell cycle

Answer 3

(1) Interphase: G1, S, G2 (+ G0 = terminally differentiate)

(2) Mitotic phase

Question 4

G1 phase (interphase)

Answer 4

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)

Question 5

S phase (interphase)

Answer 5

Nuclear DNA replicated

Question 6

G2 phase (interphase)

Answer 6

Second growth phase 
Nuclear envelope forms around nucleus 
Check for replication errors 
Cont. cell growth in prep for division
Centromeres contain centrioles

Question 7

G0 phase

Answer 7

Terminal differentiation, leave cell cycle

Question 8

Mitosis

Answer 8

Distribute (duplicated) chromosomes equally between 2 potential daughter cells

Question 9

1. Prophase (mitosis)

Answer 9

Chromosomes visible in nucleus 
Condense, shorten 
Nucleolus disappear 
Centrioles migrate to opp poles 
Microtubules form spindle fibres

Question 10

2. Prometaphase (mitosis)

Answer 10

Nuclear envelope dissolves
Mitotic spindle move to nuclear area
Chromosomes attach to spindle at kinetochores

Question 11

3. Metaphase (mitosis)

Answer 11

Chromosomes move to spindle equator (metaphase plate)

Kinetochore ensures anaphase not begin until all chromatid pairs aligned at equator = metaphase checkpoint

Question 12

4. Anaphase (mitosis)

Answer 12

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

Question 13

5. Telophase (mitosis)

Answer 13

Chromosomes uncoil
Nuclear envelope reassemble
Nucleolus reforms

Question 14

Cytokinesis

Answer 14

Cell division = 2 identical daughter cells
Position of cytoplasmic division defined by spindle equator
Plasma membrane indented = cleavage furrow
Constricts cell until division

Question 15

Cell cycle control

Answer 15

Cyclin-dependent protein kinases
Controls HIGHLY CONSERVED during eukaryotic evolution
Lose control = tumourigenesis

Question 16

Cell cycle checkpoints

Answer 16

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

Question 17

Cancer

Answer 17

Deregulation of cell cycle

Defects in checkpoints: repair proteins not assemble properly, no cell cycle response to DNA break signal

Question 18

Meiosis

Answer 18

Produce gametes w/ haploid no. chromosomes

Genetic diversity

Question 19

Meiosis I

Answer 19

Reduction division

Follows normal S phase in primary gametocytes (DNA duplicated)

Question 20

Prophase I (meiosis)

Answer 20

Chromatids cross over - exchange genetic info between homologous pairs = chiasma formation
Mix maternal and paternal alleles

Question 21

Metaphase I + Anaphase I (meiosis)

Answer 21

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

Question 22

Meiosis II

Answer 22

Follow meiosis I
No intervening S phase
4 gametes produced

Question 23

Metaphase II (meiosis)

Answer 23

Split chromatids by divide centromeres

Question 24

Anaphase II + Telophase II (meiosis)

Answer 24

Chromatids migrate to opp poles

Second meiotic division

Question 25

Generation of variation (meiosis)

Answer 25

Crossing over (prophase I) 
Independent assortment of maternal and paternal homologs (meiosis I)

Question 26

Genetic linkage

Answer 26

Genes loci close on same chromosome = less likely separate via recombination, LINKED
Gametes w/ parental genotype more common than recombinants, more likely co-inherited

Question 27

Ataxia-telangiectasia (clinical)

Answer 27

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