Mitosis, Meiosis, Cell death Flashcards
1
Q
purpose of cell cycle
A
- regenerative: replace cells that have died (mitosis)
- reproductive: perpetuate species (meiosis)
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
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)
4
Q
G2 (gap 2) phase
A
- cell prepares for mitosis by synthesising components to ensure survival and functionality of daughter cells
5
Q
early prophase (mitosis)
A
- chromatin condenses to form chromosomes w/ 2 sister chromatids
- nuclear envelope begins to break apart
- nucleolus disappears
6
Q
late prophase (mitosis)
A
- nucleus disappears
- spindle forms in cytoplasm
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)
8
Q
anaphase (mitosis)
A
- sister chromatids pulled by spindle to opposite poles to create 2 separate chromosomes instead of two attached chromatids
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
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)
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
12
Q
which cells can undergo meiosis?
A
- germ(line) cells - these produce 4 non-identical gametes
- NOT somatic cells
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
14
Q
meiosis II
A
- same as mitosis but interphase is skipped because there is already a chromosome to split
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
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
- cell shrinkage: cascades break down cytoskeleton: cytoplasm appears dense and organelles appear tightly packed
- pyknosis: chromatin condenses into patches against the nuclear envelope
- karyorrhexis: nuclear envelope breaks down and DNA becomes fragmented
- blebbing: cell membrane breaks off into irregular buds (blebs)
- 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
