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the cell cycle Flashcards

1
Q

why do somatic cells divide = mitosis

variation ?

A
  1. growth
  2. tissues/organ maintenance
  3. tissue repair

= genetic stability

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2
Q

why do germ cells divide = meiosis

variation ?

A

sexual reproduction

= genetic variation

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3
Q

mitosis & why

A

allows somatic cell to duplicate its contents & divide in two

parent cell (2n) –> daughter cell (2n) x2

= pass on genetic information to the next generation to produce two genetically identical daughter cells

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4
Q

4 major phases mitosis

A
  1. G1 (interphase)
  2. S (interphase)
  3. G2 (interphase)
  4. M (mitosis & cytokinesis)
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5
Q

functions of gap phases (G1 & 2)

A
  • double protein mass
  • duplicate organelles
  • production & assembly of proteins for the next phase
  • contain the checkpoints
  • seperate S & M
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6
Q

S phase =

interphase

A

chromosome duplication

  1. exact copy of each chromosome is made during the DNA replication = sister chromatids
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7
Q

what holds together sister chromatids & maintains alignment (2 different things)

A

centromeres

cohesin complexes

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8
Q

M phase =

A

consists nuclear division (mitosis) & cellular division (cytokinesis)

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9
Q

what are the phases in mitosis (M phase)

A
  1. prophase
  2. metaphase
  3. anaphase
  4. telophase
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10
Q

Prophase (mitosis)

x5

A

in the nucleus
1. chromosomes condense (condensin complex)

  1. kinetochore complexes bind to centromeres
  2. centrosomes move to opposite poles
  3. centrioles build long polymers of tubulin = mitotic spindle
  4. nuclear envelope starts to break
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11
Q

Metaphase (mitosis)

A
  1. nuclear envelope disintegrates
  2. spindle microtubules from each pole attach to chromosome kinetochores
  3. kinetochore-microtubules exert tension on chromatids
  4. chromosomes align on spindle equator (the metaphase plate)
  • dynamic assembly-disassembly of microtubules search & capture chromosomes & align along metaphase plate
  • sensing mechanisms correct inappropriate kinetochore attachements

***metaphase/anaphase checkpoint

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12
Q

3 types of microtubules in the mitotic spindle

A
  1. astral microtubules = cell anchoring
  2. kinetochore microtubules = kinetochore attachment
  3. interpolar microtubules = extension & contraction
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13
Q

metaphase/anaphase checkpoint = APC/C = spindle checkpoint

if activated?

A

= are all chromosomes/kinetochores attached correctly to the mitotic spindle

  • sister chromatids must be stably bi-orientated on mitotic spindle
  • dynamic assembly-disassembly of microtubules search & capture chromosomes & align along metaphase plate
  • sensing mechanisms correct inappropriate kinetochore attachements
  1. if activated sets off a cascade that results in cohesin cleavage & sister chromatid release
  2. M phase cyline (end of mitosis/exit from cell cycle)
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14
Q

Anaphase (mitosis)

A
  1. sister chromatids seperate
  2. cleavage of cohesin initiates metaphase-anaphase transition
  3. attached chromatids move to each pole
  4. poles themselves move further apart (late anaphase)
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15
Q

specific spindle movement in anaphase (mitosis)

A
  1. kinetochore microtubules shorten
  2. polar microtubules from each end interdigitate & push apart
  3. astral microtubules attach to cell membrane & pull spindle poles apart
  4. motor protein role
    - kinesins +
    - dyneins -
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16
Q

Telaphase (mitosis)

A
  1. nuclear envelope reforms
  2. chromatids de-condense
  3. mitotic spindle breaks down
  4. exit from mitosis
17
Q

cytokinesis (mitosis)

A
  1. contractile ring forms around cell perimeter (actin & myosin)
  2. pulls the plasma membrane inward
  3. cell separates into two daughter cells

= cell division

18
Q

why are cell cycle events controlled

A

to maintain genomic stability

19
Q

G1 start site (mitosis) is stimulated by

A

mitogens = stimulate irreversible entry into cell cycle

20
Q

mitogen & 3 examples

A

chemical substance that triggers a cell to start the cell cycle e.g., certain growth hormones, cytokines, hormones

21
Q

G1/S checkpoint

A

check for DNA damage, nutrients, anti-mitogens..

22
Q

what do mitogens trigger

A

cyclin D gene transcription

23
Q

what is cyclin D required for

A

passing the restriction point in mitosis

  • provide substrate specificity & switch for activation of CDK
24
Q

what does cyclin D bind to

A

CDK = cyclin-dependent kinase = promotes or inhibits downstream events

  • initiates phosphorylation
  • phosphatase turns off
25
Q

what determines the action of CDK

A
  • the cyclin D binding, different throughout the cycle
26
Q

does CDK expression change

A

no but CDK activity does

27
Q

example of CDK in metaphase

A

M cyclin activates CDK causing phosphorylation which breaks down nuclear membrane

28
Q

G2/M checkpoint

A

DNA damage/integrity?

All DNA replicated?

29
Q

G1/S checkpoint

A

nutrients, growth signals?

DNA damage integrity?

30
Q

what regulates cyclin destruction & mitosis exit

A

ubiquitin ligases

31
Q

cell cycle control

A
  1. ensures conditions for replication & division
  2. ensures events occur in a set sequence
  3. ensures each process completed before moving to the next
  4. governs progression at 3 major transitions (checkpoints)
32
Q

Meiosis

A

diploid germ cell (2n) –> production of haploid cells (n) –> differentiate into specialised reproductive cells (sperm or ovum) –> fertilisation (fusion of gametes = 2n)

33
Q

Meiosis phases

A
  1. interphase = homologous pair of replicated chromosomes
  2. prophase I = homologous chromosomes pair up & exchange fragments (crossing over)
  3. metaphase I = homologous pairs line up at the metaphase plate
  4. Anaphase I = homologous seperate to opposite ends of the cell (sister chromatids stay together
  5. telephase I = newly forming cells are haploid (n=2) each cell has two non-identical sister chromatids
34
Q

Meiosis 2 rounds of division

A
  1. Homologous chromosomes seperate

2. sister chromatids separated (reflects mitosis)

35
Q

Prophase I (meiosis) & define chiasmata

A
  1. zygotene - synapsis = the connecting of the homologous chromosomes to form a tetrad
  2. pachytene = homologous recombination between paternal & maternal homologs (nonsister), exhange alleles
  3. diplotene = paired homologu chromosomes begin to seperate & chiasmata becomes visible

chiasmata = assist with attachement to opposite spindle poles & normal segregation of homologu chromosomes in meiosis I –> if not correct segregation could cause aneuploidy

36
Q

Metaphase I (meiosis)

A
  1. bivalent alignment at metaphase is random

- independent assortment = increase genetic variation

37
Q

Metaphase II (meiosis)

A

= random assortment

  1. sister chromatid seperation however they can be non identical
    - random orientation on metaphase plate = increase genetic variation

hc (11 decks)

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