WEEK 3 Flashcards
(29 cards)
What are the 5 steps in the cell cycle and the 2 phases
mitotic phase - mitosis and cytokinesis (10%)
interphase - G1, S phase and G2 (90%)
what is mitosis
asexual cell division of eukaryotic cells that produce genetically identical daughter cells
what is cytokinesis
cell splitting at the end of mitosis or meiosis
what is the G1 phase of interphase
growth phase –> increase in cell size and organelles
what is the S phase of interphase
DNA synthesis (chromosome duplication)
what is the G2 phase of interphase
growth phase
what is the purpose of having these “stages” in the cell cycle
each stage serves as a checkpoint before continuing further into the cycle
how do bacteria duplicate
binary fission
- chromosomes duplication (origin of replication)
- go to opposite ends of the cell
- plasma membrane grows inwards
- cell splits in 2 (FtsZ enzyme pinches cells into 2)
- 2 daughter cells form
what is the chromatid and centromere
centromere = where the sister chromatids are both attached the closest
chromatid = after dna replication chromosome consists of 2 identical sister chromatids
what are the 5 phases of mitosis.
IPMAT
INTERPHASE
PROPHASE
METAPHASE
ANAPHASE
TELOPHASE
What happens during Interphase and which stage is it in mitosis?
1st stage
Chromosomes replicated
Nuclear envelope still intact
Centrosomes found together (site of microtubule growth)
No mitotic spindle yet
What happens during Prophase and which stage is it in mitosis?
2nd
Mitotic spindle begins to form at centrosomes
Centrosomes begin to separate to opposite sides of cell
Chromatin condenses into discrete chromosomes
Nuclear envelope breaks down → absorbed into ER
What happens during Metaphase and which stage is it in mitosis?
3rd
Chromosomes align on metaphase plate
Kinetochores attach to microtubules (centromere + microtubule complex)
What happens during Anaphase and which stage is it in mitosis?
4th
Daughter chromatids split and move to opposite poles via microtubules and microtubule motors (Dynein and Kinesins)
What happens during Telophase and which stage is it in mitosis?
5th
Chromatin decondenses
Nuclei reform
Spindle disassembles
Cytokinesis begins
When does cytokinesis occur
after telophase
what is the mitotic spindle and how does it work
made of microtubules that grow from the centrosomes
Dynein binds to plasma membrane and walks along microtubule pulling it towards the membrane
Kinesin located at regions of microtubule overlap and push different microtubules of each centrosome away from each other
how are microtubules “pulled” towards the ends of the cell
microtubules are shortened at the kinetochores end (not the centrosome end) and shortened by the breaking down (hydrolysis) of tubulin subunits (alpha and beta) by dynein
how does animal cytokinesis take place?
- use cleavage furrow
- at metaphase plate
- cell divides from outside to inside
- furrow pinches cell into 2
- use actin microfilaments and myosin
how does plant cytokinesis take place?
- Vesicles from Golgi apparatus moving alone microtubules fuse
- Cell plate enlarges to divide cell in half
- New cell wall formed from contents of cell plate
- Divides from inside outwards
- Uses microtubules and kinesin
what is meiosis
produces haploid daughter cells with half the DNA that fuse to make offspring and grow via mitosis
what is haploid and diploid cells
haploid - 23 in humans (n)
diploid is 46 (2n)
what are origins of genetic diversity
crossing over
independent assortment
random fertilisation
how does crossing over take place
happens in prophase
homologous pairs exchange segments of DNA
synapsis forms - held together by proteins (synaptonemal complex)
crossing over takes place
complex dissassembles - leaving behind the chiasma (site where chromosomes are still held together)
