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FunMed Week 4 - cancer > Cell Cycle and Cell Division > Flashcards

Cell Cycle and Cell Division Flashcards

1
Q

why is cell division important? (4)

A

evolution of life

cell repair / enhancement

genetic variation

growth

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2
Q

what are sister and homologous chromosomes?

A

sister chromatids are identical copies of same chromatid (i.e both from mother / father)

homologous chromosome: a pair of chromosoemes, each derived from one parent

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3
Q

the process of cell divison is broadly divided into which phases?

A
  1. interphase: DNA replication

composed of: G1 phase (cell growth), S phase (DNA synthesis occurs) and G2 phase (cell growth)

  1. mitotic phase (M phase): nucleus divides

3. cytokinesis: cytoplasm divided into two daughter cells

CELL IS MOSTLY IN INTERPHASE

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4
Q

Explain each phase of a bit more :)

A

G0 phase: cells outside of cycle and have stopped dividing. can return to G1 phase.

G1 phase: normal growth phase. prep for DNA synthesis

S phase: DNA synthesised and duplicated

G2 phase: cell prepares for cell division

M phase: proper cell division

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5
Q

what are the G phases?

A

gap / growth phases:

  • cell undergoes normal function.

- NOT growing or replicating

  • allows cell time to monitor the env to check conditons correct for replication
  • act as regulatory phases / checkpoints: indicate of cell should continue dividing or undergo apoptosis
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6
Q

Explain the S phase

A

Synthesis Phase

DNA duplicated: 23 -> 46

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7
Q

explain the M phase

A

(each chromosome has doubled)

Mitotic phase:

Made of 4 stages:

Prophase, Metaphase, Anaphase, Telophase

then have cytokinesis (splitting of cytoplasm into 2)

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8
Q

Explain what occurs in prophase

A
  • nucleolous dissapears (dont need DNA that codes for ribosomes cell division)
  • chromatin condenses, linked by centromere

- cytoplasmic microtubules dissasemble (and form mitotic spindle)

  • mitotic spindle forms at two centrosomes (at opposing ends of cell)
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9
Q

explain what occurs in metaphase

A

pro-metaphase

  • nuclear envelope dissolves
  • microtubules form a radiating array
  • microtubules attach to the centromere of the chromosomes at the kinetochore (part
  • centrosome moves towards opposing ends of cell

Metaphase

  • chromosomes are aligned by mitotic spindle towards the centre of the spindle called the metaphase plate
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10
Q

how do kinetochores form

A

one microtubule from one side attaches to kinetochore on one side of one sister chromatin. another microtubule attaches to other side of other kinetochore on other sister chromatid

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11
Q

explain anaphase

A

Anaphase:

  • mitotic spindle microtubules start to retract
  • pulls sister chromatids apart through kinetochores
  • spindles move further apart from the poles

MOST CRITICAL PART OF MITOSIS WHICH ENSURES EQUAL DISTRIBUTION OF CHROMOSOMES BETWEEN CELLS

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12
Q
A
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13
Q

what is cohesin?

What is non-disjunction?

A

cohesin: protein complex that regulates seperation of sister chromatids during cell division. hold chromatids together till anaphase

non-dysjunction: one sister chromatin wont let go of other sister chromatin -> both get carried to one side = get one extra / less chromosome

chesionpathies - leads to extra / less chromosomes due to non-dysjunction. monosomies . trisomies e.g. D/S

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14
Q

explain telophase and cytokinesis

A

Telophase

  • chromosomes reach poles of mitotic spindle
  • mitotic spindle dissapears
  • new nuclear envelope

cytokinesis:

  • actin and myosin form contractile ring - pinches cytoplasm until splits (after forming a cleavage furrow)

-

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15
Q

how many phases are there in meiosis? explain

what does error in meisois lead to?

A

meiosis I: (2N to N). (PMAT I) homologous chromosomes are separated.

meiosis II: (PMAT II). sister chromatids are seperated

errors in meisosis: aneuploidy - leading cause of miscarriage

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16
Q

explain meiosis prophase I

A

(same as in mitosis but..)

  • homologous chromosomes align at the centre of the cell (insead of sister like in mitosis)
  • homologous chromosomes are joined at points called chiasmata

- crossing over / recombination can occur at chiasma

-

17
Q
  • explain process of crossing over / recombination. when does it occur?
  • explain what independent assortment. when does it occur?
A

Crossing over

MAIN SOURCE OF GENETIC VARIATION BETWEEN GENERATIONS = zygote

  • essentially a balanced translocation
  • occurs at chiasmata
  • can occur in prophase or metaphase

Independent assortment

  • sister chromatids during metaphase II, are randomly allocated from one side to the other
18
Q

explain metaphase and anaphase I (for meiosis)

A

Metaphase

  • same as mitosis
  • Homologous chromosomes move to centre of cell and face opposite ends of spindle (randomly = source of variation)

Anaphase

  • same as mitosis
  • sister chromatids remain attached at this stage so each pole gets two copies of the same chromosome
19
Q
A
20
Q

explain telophase and cytokinesis I (for meisois)

A

very similar to telophase and cytokinesis of mitosis. BUT can have:

cells can undergo interkensis / interphase II: no DNA replication occurs during this stage

21
Q

what is difference between meiosis I and meiosis II? (general)

A

during anaphase in meisois II, get seperation of sister chromatids rather than homologous chromsomes

meisois II: more similar to mitosis

22
Q

when can non-disjunction occur?

A

meisois I or II

(also in mitosis)

23
Q

when does

A
24
Q

which is most common non-disjunction disease?

A

trisomy 21 - Down Syndrome

25
Q

how is the cell cycle controlled? name and explain the checkpoints

A

- very tightly regulated (if escape leads to cancer)

G1 checkpoint: end of G1. controls if cell enters S phase. is environment favourable? checks for growth factors, nutrients, cell size and DNA damage

G2 checkpoint: end of G2. environment favourable? is all DNA replicated? checks for cell size, DNA damage and DNA replication

Metaphase checkpoint: are all chromsomes attached to spindle?

26
Q

what happens if cell fails checkpoint?

A

cell cycle can be stopped (senesence) or die by apoptosis

27
Q

which proteins regulate cell divison?

A
  1. Cyclins (cylin A,B, D) - allow cell cycle to continue
  2. cyclin dependent kinases (CDK) add P groups to cyclin -> activates the cyclins

3. cyclin dependent kinases inhibitors (CDKIs)

depending on if CDK or CDKI is more prominant - regulates cell cycle

28
Q

when is each cyclin actived?

A
  • G1 checkpoint passed: activates cyclin D (regulates early G1 phase) and cyclin E (regulates early G1 phase and triggers S phase)

- S checkpoint passed: activates cyclin A (cyclin A acitvates DNA replication in S phase and movement into G2 phase)

- G2 / M checkpoint passed: activates cyclin B (takes cells into mitosis)

29
Q
A
30
Q

what is p53? why important?

A

P53 - guardian of the genome!

- blocks progression of cell cycle by of synthesis p21 (a CDKI) which inhibits CDK2 ( which inhibits activation of cyclin E and A)

- is an important tumour suppressor gene

31
Q

explain retinoblastoma

(dont need to know in detail)

A

mechanism:

  • retinoblastoma protein (Rb): tumour suppressor. generally switched on by p53/p21 & switched off by cyclin E/CDK
  • Rb prevents DNA syn by binding E2F protein and preventing from going into S phase.
  • mutation leaves uncontrolled cell division

who?

- young children

32
Q

how does chemotherapy work? (3)

A

prevents cancer cell cycle from dividing:

a) most are anti-mitotic (prevents mitotic spindle forming). not selective - kills normall cells

b) biologicals - selective drug that target proteins essential for growth (e.g. CDKs). monoclonal antibodies

c) anti-hormonal drugs - block production of hormones of their receptors.

33
Q

anti-mitotic drugs?

A
  • anti microtubule agents. inhibit assembly

- vinca alkaloids and taxanes are two main groups.

  • (need to know other mitotic blockers?)

FunMed Week 4 - cancer (9 decks)

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