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HNC Applied Science in Biology and Chemistry > Cell Biology - Outcome 4 > Flashcards

Cell Biology - Outcome 4 Flashcards

Cell Replication and Division

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1
Q

what two processes must a cell undergo to grow and divide?

A
  • replication: doubling of chromosome complement to create 2 copies of each piece of DNA
  • mitosis: nuclear division that results in each daughter cell receiving full chromosome complement
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2
Q

what are the phases of the cell cycle?

A
  • G1
  • S
    -G2
  • M
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3
Q

what phases are known as interphase?

A
  • G1
  • S
  • G2
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4
Q

what do the phases of the cell cycle depend one to move from one phase to the next?

A

cyclin-dependent kinases (CDKs)

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5
Q

what do CDKs do?

A

activate other proteins by adding phosphate groups (phosphorylation)

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6
Q

how do CDKs become active?

A

they must bind to cyclins

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7
Q

what happens in the G1 phase?

A
  • as level of cyclin increases, it increasingly binds to CDK
  • signals cell to prepare for chromosomes for replication
  • cell will be growing
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8
Q

what happens during G0 phase?

A
  • resting stage (temp or perm)
  • not actively growing and dividing but they are often still highly metabolically active carrying out cellular functions
  • phase is brought about by absence of cues for growth and division - genes controlling mitosis are actually repressed
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9
Q

which cells temporarily enter G0?

A
  • lymphocytes which remain in that phase until they encounter an antigen
  • when they do - they re-enter G1, becoming self-replicating colonies
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10
Q

what happens during the S phase?

A
  • synthesis of DNA
  • occurs at slightly different times within each individual cell
  • certain points in the cell cycle some cells will be 4n whilst some are still 2n (diploid)
  • after replication two sister chromatids are held together in a dyad by centromeres, until separated by mitosis
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11
Q

what happens during the Gap 2 phase (G2)?

A
  • the level of cyclin E falls, while cyclin B begins to rise
  • centrosomes (including centrioles) also duplicate - the centrioles have a significant role to play during mitosis
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12
Q

what is mitosis?

A

the division of the nucleus

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13
Q

what does the M stage involve?

A
  • nuclear division and cytokinesis
  • triggered by mitogens
  • formation of M-phase promoting factor which is a complex of Cdks and cyclins
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14
Q

what are the 4 phases of mitosis?

A
  • prophase
  • metaphase
  • anaphase
  • telophase
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15
Q

what happens during prophase?

A
  • begins with m-phase promoting factor
  • the chromosomes shorten and condense
  • nuclear membrane disintegrates
  • centrioles move apart to opposite poles of the nucleus
  • bundles of fibre protein fibres called mitotic spindles grow out from centrioles
  • two kinetochores appear on centrosomes of each chromosome
  • mitotic spindle fibres attach to kinetochores
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16
Q

what happens during metaphase?

A
  • chromosomes still attached by spindle fibres to poles
  • line up across centre line of cell (metaphase plate)
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17
Q

what happens during anaphase?

A
  • m-phase promoting factor activates anaphase promoting factor (APC/C) by phosphorylation to begin anaphase
  • spinde fibres contract and pairs of chromosomes now become separate and migrate to opposite poles of cell, dragging with it one of chromatids from each chromosome
  • APC/C also switches on synthesis of G1 cyclin - initiates next cell cycle
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18
Q

what happens during telophase?

A
  • with newly separated chromatids (chromosomes) clustered at each end of cell - nuclear membrane forms around each cluster
  • chromosomes relax from highly condensed form to become fine, thread-like chromatin
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19
Q

what happens during cytokinesis?

A
  • separation of the cytoplasm
  • belt of protein actin forms around middle of cell between reformed nuclei
  • tightens until it pinches the cell into 2 daughter cells
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20
Q

what are the 2 types of cell cycle checkpoints?

A
  • DNA damage checkpoint
  • spindle checkpoints
21
Q

when do DNA damage checkpoints occur?

A

during G1, S and G2 phase (interphase)

22
Q

when do spindle checkpoints occur?

A

during M phase

23
Q

what happens during DNA damage checkpoint in G1?

A
  • p53 protein holds cell in G1 until DNA damage is repaired - prevents replication of damaged DNA
  • if damage is irreparable, protein can induce apoptosis- cell will commit suicide
24
Q

what happens during DNA damage checkpoint in G2?

A
  • G2 checkpoint monitors Okazaki fragments on lagging strand of replicated DNA
  • cell will not move to M phase until all fragments have been incorporated into continuous DNA strand by removal of RNA primers and closing of gaps by ligase
  • ensures DNA has been replicated successfully before mitosis occurs
25
Q

what happens during spindle checkpoints?

A
  • assess formation of spindles
  • holds cell in M phase - prevents cytokinesis
  • checks made on attachment of fibres to kinetochores and which direction fibres pull chromosomes
  • apoptosis can be triggered if damage is severe
26
Q

what can the human chromosome complement be represented by?

A

a karyotype

27
Q

what are gonads

A

ovaries or testes

28
Q

what are special diploid cells in the gonads called?

A

gamete mother cells

29
Q

what is meiosis?

A

a process that has 2 stages and produces 4 haploid gametes

30
Q

what happens in meiosis I?

A
  • diploid gamete mother cell becomes 2 haploid daughter cells
  • mitosis occurs
31
Q

what happens in prophase I in meiosis?

A
  • homologous chromosomes pair up to form bivalents
  • each chromosome consists of a chromosome of pairs chromatids - each bivalent consists of four chromatids with 2 centromeres
  • spindle fibers emerge from centrioles and kinetochores form on chromosomes
  • one kinetochore forms on each chromosome dyad, not one on each chromatid
32
Q

what happens in metaphase I in meiosis?

A
  • spindle attached bivalents align along metaphase plate
33
Q

what happens in anaphase I in meiosis?

A
  • chromosome dyads are pulled apart by spindle fibres to opposite poles of cell
34
Q

what happens in telophase I in meiosis?

A
  • nuclear membrane reforms and cytokinesis commences
  • each cell contains only one maternal or one paternal version of each chromosome - haploid
35
Q

what happens in meiosis II?

A
  • only 23 chromosomes are replicated into each separate cell rather than diploid complement of 46 replicated in meiosis
  • at end of meiosis, each gamete mother cell therefore produces 4 gametes
36
Q

what dies replication of a single chromosome produce?

A
  • two identical chromatids
  • each carry exactly the same versions of each allele ( alternative versions of same gene) in exactly the same loci
37
Q

where do two copies of each chromosome come from?

A
  • one copy from the mother
  • one copy from the father
    these are not identical
38
Q

will a gamete that receives the maternal version of a chromosome be the same as a gamete that receives a paternal version?

A

no

39
Q

what is a source of variation that happens during prophase I?

A
  • homologous chromosome pair together, chiasmata form
  • points at which some of the genetic material from maternal and paternal versions of same chromosome become entangled
40
Q

what happens to the homologous pairs are separated at anaphase I when they formed chiasmata?

A
  • chiasmata leads to exchange of genes between one chromatid of maternal and paternal chromosomes
41
Q

what will happen to 2 out of the 4 gametes if cross over occurs at the chiasmata?

A
  • each gamete mother cell will not contain pure maternal or paternal chromosomes but rather a mixture of the two
42
Q

what is cancer a result of?

A

the degradation of the regulator mechanisms of the cell cycle

43
Q

which regulatory genes must be affected for cancer to develop?

A
  • oncogenes, cell division promoters
  • tumour suppression genes, inhibit cell division
44
Q

describe what happens if p53 is mutated or damaged?

A
  • DNA damage will persist
  • cells will continue to divide
45
Q

what is an example of a tumour suppressor gene?

A

p53

46
Q

what is an example of an oncogene?

A

Ras

47
Q

describe what happens if Ras is mutated or damaged?

A
  • once activated cannot be de-activated
  • constantly stimulates cell division
48
Q

what are other checkpoints that cancerous cells ignore?

A
  • density dependent inhibition (stop cells diving if crowded)
  • anchorage dependence (cells require attachment to solid base before division)

HNC Applied Science in Biology and Chemistry (7 decks)

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