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17 Cards in this Set

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Mitosis - Definition
a type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus, typical of ordinary tissue growth (split into interphase and M phase)
Mitosis - Interphase
- consists of G1, S and G2 phase
- cell grows, doubling in protein content
- organelles double in size or number
- during the S phase DNA is synthesised and the centrosome duplicates
- the gaps act as cell checks to make sure everything is ready for the next stage
Mitosis - Mphase (prophase)
- chromosomes condense
- mitotic spindle (microtubules and proteins) form
- centrosomes move apart
- protein complexes (KINETOCHORE) forms at centromere of the chromosomes
Mitosis - Mphase (prometaphase)
- nuclear envelope breaks down which allows microtubules access to the chromosomes
- chromosomes attach to the microtubules via the KINETOCHORE COMPLEX
Mitosis - Mphase (metaphase)
-chromosomes align at the equator
- sister chromatids attach to opposite poles by kinetochore microtubules (each chromosome attaches to 2 spindles)
Mitosis - Mphase (anaphase)
- cohesive link between sister chromatids is released
- kinetochore microtubules shorten
- centrosomes move apart
- sister chromatids move to opposite poles
Mitosis - Mphase (telophase)
- chromatids reach poles
- new nuclear envelope forms from fragments attached to individual chromosomes
- contractile ring beings to form around the equator in preparation cytokinetic division
Mitosis - Mphase (cytokinesis)
- the ring contracts partitioning cytoplasm into two daughter cells
- each cell contains 1 nucleus, 1 centrosome, a share of all the organelles
- DNA de-condenses and the cell returns to resting interphase (G1)
The cell cycle - The cytoskeleton
- increased instability in cytoskeleton, motor proteins move components
- nuclear laminar disassembles before mitosis
-actin involved in ring contraction during cytokinsis
- KINETOCHORE MICROTUBULES: shrink and grow until they attach to the chromosomes, the motor proteins (+&-) pull chromosomes around until aligned, in anaphase they shorten and motor proteins move chromatids towards centrosome.
The cell cycle - Hows it controlled (check points)
- key check points which make sure everything is correct for the next stage:
1) restriction point (end of G1), environmental check (size, nutrients, growth factors) and DNA damage check
2) G2-M transition, environment check (size), DNA damage check and replication complete.
3) Meta-anaphase transition, chromosome attachment check.
The cell cycle - Hows it controlled (CDKs)
- cyclin dependant kinases, need cyclins to be turned on, levels of cyclin rise and fall during cycle,
- different Cdk-cyclin complexes regulate different transitions.
-kinases phosphorylate target proteins
- nuclear lamins trigger depolymerisation
Meiosis - Definition
-a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes and plant spores
- parental cell divides twice but DNA only divides once
- have 46 diploid no and 23 haploid no in humans
Meiosis - Advantages
- allows the mixing of traits for increased genetic diversity and increased chance of selective advantage.
- this is achieved by random selective of which chromosome is distributed to the gamete and by recombination (crossing over)
Meiosis - Interphase 1
- DNA replicates to form a pair of chromatids
Meiosis - Prophase 1
- leptotene: DNA condenses and increases in packaging factor
- Zygotene: homologous chromosomes align and link via synaptonemal complexes (synapsis)
- Pachytene: pairs of chromosomes coil, crossing over one another (recombination)
- Diplotene: synaptonemal complexes break down, pairs of chromosomes are linked at crossover points (chiasmata)
- Diakinesis: chromosomal condensation reaches maximum
Meiosis - Metaphase 1, anaphase 1, telophase 1
- same for mitosis but with 23 pairs of chromosomes instead 46 pairs of chromatids separate to the two poles (goes from diploid to haploid) known as reduction division
Meiosis - Metaphase 2, anaphase 2, telophase 2 and cytokinesis 2
- interphase break occurs but no secondary replication of DNA
- Sister chromatids are now separated by spindle fibres, creating 4 haploid cells with half the original DNA content