Intro Molecular Biology REVISION (pt1) Flashcards
1
Q
Stages of the cell cycle in eukaryotic cells
5
A
- G1
- S
- G2
- Mitosis (+cytokinesis)
2
Q
what happens in the interphase ?
A
- G1
- S
- G2
3
Q
what happens is G1 ?
A
- Growth phase
- Increase metabolic/biosynthetic activity
3
Q
what happens is G1 ?
A
- Growth phase
- Increase metabolic/biosynthetic activity
4
Q
what 3 options doe the G1 phase have ?
A
- To continue cell cycle and enter S phase
- Stop cell cycle and enter G0 (resting phase) for undergoing differentiation
- Become arrested in G1 phase and entre the G0 phase or re-entre cell cycle
5
Q
what happens is the S phase ?
A
DNA synthesis commences
6
Q
what happens in the G2 phase ?
A
- Occurs after DNA replication and is a period of protein synthesis and rapid cell growth to prepare the cell for mitosis
- Before proceeding to mitotic phase, cells must be checked at the G2 checkpoint for any DNA damage within the chromososmes
7
Q
what happens in the Mitosis ?
A
Consists of nuclear division (karyokinesis)
8
Q
what are the stages of Mitosis
A
- Prophase
- Metaphase
- Anaphase
- Telophase
9
Q
what happens in the prophase ?
A
- cell prepares to divide by tightly condensing its chromosomes
- initialisation of mitotic spindle formation
- Gene transcription ceases until late anaphase to early G1
- Centrosomes coordinate cell’s microtubules
10
Q
what happens in the prometaphase ?
A
- Phosphorylation of nuclear lamins = nuclear envelope disintegrates into small membrane vesicles
- microtubules invade the nuclear space
- late stage = kinetochore microtubules attach to chromosomal kinetochores
11
Q
what happens in the metaphase ?
A
- 2 centrosomes begin to pull chromosomes towards opposite poles of the cell
- checkpoint to guarantee that kinetochores have properly attached to the mitotic spindle + alignment of chromosomes along metaphase plate
12
Q
what happens in anaphase?
A
- cohesins bind sister chromatids together and are cleaved, forming 2 identical daughter chromosomes
- kinetochore microtubules shorten which pull the daughter chromosomes to opposite ends of the cell
- polar microtubules push against each other elongating the cell
- late stage = chromosomes reach overall maximal condensation level
13
Q
What happend during telophase ?
A
- microtubules lengthen, elongating cell further
- new nuclear envelope formed around each separated daughter chromosome form membrane vesicles of parent cell’s old nuclear envelope
- chromosomes begin to “relax” or decondense
14
Q
Cytokinesis
A
NOT A PHASE OF MITOSIS
- Cleavage furrow (pinch) containing a contractile ring, develops where the metaphase plate used to be, pinching off the separated nuclei
- Each daughter cell has a complete copy of the genome of its parent cell
15
Q
Meiosis
key points
A
- cell division of germ cells in sexually reproducing organisms to produce gametes (e.g. sperm or egg cells)
- 2 rounds of division = 4 cells with each ONE copy oh each chromosomes (haploid)
- paternal and maternal genetic information on chromosomes are crossed, creating new code combination on the chromosomes
- during fertilisation, haploid cells produced by meiosis from male and female fuse = 2 copies of each chromosome again (zygote)
16
Q
Phases of meiosis
A
- meiosis I and meiosis II divided into Karyokinesis I and Cytokinesis I and Karyokinesis II and Cytokinesis II respectively
- same preparatory state as mitosis ( G1,S,G2)
- Meiosis I and II are each divided into:
Prophase
Metaphase
Anaphase
Telophase
17
Q
Meiosis I - Prophase 1
A
- longest phase
- Homologous maternal and paternal chromosomes pair, synapse, and exchange genetic information (by homologous recombination), forming at least one crossover per chromosome
18
Q
what happens in meiosis I - prophase 1?
pt (2)
A
- this stage in divided into series of substages names according to the apperance of chromosomes:
1. Leptotene
2. Zygotene
3. Pachytene
4. Diplotene
DIAKINESIS - chromosomes condense further
- nuclear membrane
disintegrates into vesicles - meiotic spindle begins to form
- (resembles prometaphase in mitosis)
19
Q
What happenes in
Meiosis I – Metaphase 1?
A
- homologous pairs move along metaphase plate
- kinetochore microtubles from both sindle poles attach to respective kinitochores
- paired homologous chromosomes alingh=n along an equatorial plane that bisects the spindle
20
Q
what happens in Meiosis I – Anaphase 1?
A
- Kinetochore microtubules shorten = pull homologous chromosomes to opposite poles
- Non-kinetochore microtubules lengthen, pushing the centrosomes farther apart
- cell elongates in separation for division down the centre
- sister chromatids remain together
- homologous are segregated
21
Q
Meiosis I – Telophase 1 & Cytokinesis
A
- first meiotic division end when chromosomes arrive at the poles
- each daughter cell had half the number of chromosomes, each chromosome has a pair of chromatids
- cell membrane is pinched = creation of 2 daughter cells
here, cytpkinesis isn’t fully complete, resulting in “cytoplasmatic bridges” enebling the cytoplasm to be shared betwee daughter cell untilll end of meiosis II
22
Q
Meiosis II – Prophase 2
A
- usually involves equational segregation or separation of sister chromatids
- disappearance of nucleoli and nuclear envelope
- shortening and thickening of chromatids
- centrosomes move to polar regions and arrange spindle fibres for 2nd meiotic division
23
Q
Meiosis II – Metaphase 2
A
- Centromeres contain 2 kinetochores that attach to spindle fibres from the centrosomes at opposite poles
- new equatorial metaphase plate is rotated by 90 degrees when compared to meiosis I – perpendicular to the previous plate
24
Q
Meiosis II – Anaphase 2
A
- Remaining centromeric cohesin, is cleaved, allowing the sister chromatids to segregate
- sister chromatids are now called sister chromosomes as they move toward opposing poles
25
Q
Meiosis II – Telophase 2 & Cytokinesis
A
- De-condensation and lengthening of the chromosomes
- disassembly of the spindle
- Nuclear envelopes re-form and cleavage or cell plate formation eventually produces a total of 4 daughter cells, each with a haploid set of chromosomes
26
Q
stages of meiosis
A
- Meiosis I – Prophase 1
- Meiosis I – Metaphase 1
- Meiosis I – Anaphase 1
- Meiosis I – Telophase 1 & Cytokinesis
- Meiosis II – Prophase 2
- Meiosis II – Metaphase 2
- Meiosis II – Anaphase 2
- Meiosis II – Telophase 2 & Cytokinesis
