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JAFFY Anatomy > Mitosis, Meiosis, Cell death > Flashcards

Mitosis, Meiosis, Cell death Flashcards

1
Q

purpose of cell cycle

A
  • regenerative: replace cells that have died (mitosis)
  • reproductive: perpetuate species (meiosis)
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2
Q

G1 (gap 1) phase

A
  • cell functions normally, organelles are duplicated (cell doubles in size)
  • usually longest phase
  • non-dividing cells e.g. neurons enter G0
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3
Q

S (synthesis) phase

A
  • DNA replicated to produce 2 copies of each chromosome
  • pre-replication complexes form
  • cell is now 4n
  • 23 pairs of chromosomes w/ 2 sister chromatids held together @ centromere (not condensed yet)
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4
Q

G2 (gap 2) phase

A
  • cell prepares for mitosis by synthesising components to ensure survival and functionality of daughter cells
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5
Q

early prophase (mitosis)

A
  • chromatin condenses to form chromosomes w/ 2 sister chromatids
  • nuclear envelope begins to break apart
  • nucleolus disappears
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6
Q

late prophase (mitosis)

A
  • nucleus disappears
  • spindle forms in cytoplasm
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7
Q

metaphase (mitosis)

A
  • spindle attaches to chromosomes @ centromeres
  • chromosomes move to equatorial/metaphase plate (along middle of cell b/n poles)
  • chromosomes are in most condensed state so can be stained to show banding patterns (most visible)
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8
Q

anaphase (mitosis)

A
  • sister chromatids pulled by spindle to opposite poles to create 2 separate chromosomes instead of two attached chromatids
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9
Q

telophase (mitosis)

A
  • nuclear membrane reassembles to surround daughter chromosomes
  • nucleoli reappear
  • cleavage appears
  • chromosomes decondense to become chromatin > once again in interphase
  • cells split during cytokinesis
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10
Q

cyclin/CDK regulation

A
  • cyclin D + CDK4 -> cyclin E: phosphorylates (inactivates) rB to to allow G1>S
  • cyclin E + CDK2 -> cyclin A: prepares for DNA replication (G1>S)
  • cyclin A + CDK2 -> cyclin B: activates DNA replication in nucleus (S phase)
  • cyclin B + CDK1 -> promotes formation of mitotic spindle + other stuff to prepare for mitosis (G2>M)
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11
Q

two proteins involved in stopping cell cycles (tumour suppressors)

A
  • Rb (retinoblastoma): can be inactivated via phosphorylation to allow G1-S transition
  • p53: activates CDK inhibitors > prevent G1-S transition
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12
Q

which cells can undergo meiosis?

A
  • germ(line) cells - these produce 4 non-identical gametes
  • NOT somatic cells
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13
Q

meiosis I

A
  • interphase: DNA replicates and cell prepares for division
  • prophase I: synapsis (pairing of homologous chromosomes) and crossing over occurs - recombination/swapping of DNA alleles
  • metaphase I: homologous chromosome pairs (tetrads) line up randomly on spindle equator
  • anaphase I: homologous chromosomes separate (whole chromosomes w/ 2 chromatids on each side)
  • telophase I and cytokinesis: nucleus reforms and homologous chromosomes separate into daughter cells
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14
Q

meiosis II

A
  • same as mitosis but interphase is skipped because there is already a chromosome to split
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15
Q

similarities between spermatogenesis and oogenesis

A
  • both only cells to undergo meiosis
  • both undergo extensive morphological (physical) differentiation
  • both can’t survive for very long if fertilisation doesn’t occur
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16
Q

differences between spermatogenesis and oogenesis

A
  • spermatogenesis: one stem cell leads to 4 spermatids (which mature into sperm) whereas oogenesis produces one ootid (which matures into an egg) and 3 polar bodies
  • oogenesis starts at birth but is interrupted until puberty, until fertilisation and then stops @ menopause, whereas spermatogenesis begins at puberty and continues until death
17
Q

3 factors during meiosis which result in genetic variation

A
  • crossing over during prophase I: random shuffling of alleles
  • independent assortment: random crossing over and lining up of homologous chromosomes (we don’t know which homologous chromosome will end up in which daughter cell)
  • random fertilisation: each egg and sperm has 8 million possible chromosome combinations
18
Q

types of non-disjunction (incorrect chromosome separation) in meiosis

A
  • sex chromosome aneuploidy: generally not too many noticeable/harmful effects
  • autosomal aneuploidy: usually result in spontaneous miscarriage b/c foetus can’t survive however if on a particular chromosome pair, they can survive through gestation
19
Q

what is apoptosis and give examples of when it occurs

A
  • regulated, programmed cell death - not harmful to surrounding tissues
  • e.g. if something goes wrong during mitosis, separation of digits, formation of lumen in organs, high rate of apoptosis during spermatogenesis
20
Q

examples of intrinsic and extrinsic signals which trigger apoptosis

A
  • intrinsic: DNA damage, changes in Ca levels
  • extrinsic: toxins, hormones, growth factors, heat, radiation, hypoxia - can either trigger or inhibit apoptosis
21
Q

process of apoptosis

A
  1. cell shrinkage: cascades break down cytoskeleton: cytoplasm appears dense and organelles appear tightly packed
  2. pyknosis: chromatin condenses into patches against the nuclear envelope
  3. karyorrhexis: nuclear envelope breaks down and DNA becomes fragmented
  4. blebbing: cell membrane breaks off into irregular buds (blebs)
  5. phagocytosis: cell breaks apart into vesicles called apoptotic bodies which are phagocytosed
22
Q

what is necrosis

A
  • unregulated, premature death of cells where they swell and burst which is toxic to other tissues
  • due to extrinsic injury, infection, cancer, poison etc.
  • necrotic tissue needs to be surgically removed because a lack of chemical signals prevents phagocytes from engulfing dead cells > build-up of dead tissue/inflammation
23
Q

chromosome division of meiosis

A
24
Q

when can non-disjunction occur and when is it the most common?

A
  • anaphase: mitosis or meiosis I or meiosis II
  • most common during meiosis I
  • also worse outcomes in meiosis I because more daughter cells are affected

JAFFY Anatomy (14 decks)

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