Cell Division Flashcards
1
Q
define cell cycle
A
- ordered seq of events
- cell divides
- forms 2 genetically identical daughter cells
2
Q
describe what occurs during interphase
A
- periods of growth + normal separate divisions
- DNA replicated + checked for errors
- protein synthesis
- mitochondria grow and divide
- chloroplasts grow and divide
- metabolic processes occur (resp)
3
Q
stages of interphase
A
G1 :
- proteins produced
- organelles replicate
- cell inc in size
S : synthesis phase
- DNA replicated in the nucleus
G2 :
- cell continues to inc in size
- energy stores inc
- duplicated DNA checked for errors
4
Q
mitotic phase
A
- period of cell division
2 stages :
- mitsosis : nucleus divides
- cytokinesis : cytoplasm divides + 2 cells produced
5
Q
G0
A
- cell leaves the cycle (temp or perm) bc:
- differentiation : cell = specialised so can’t divide. Carry out it’s function and won’t enter cell cycle again
- DNA = damaged = not viable. Damaged cell can’t divide and enters permanent cell arrest (G0)
- some cells that enter G0 are stimulated to go back into cell cycle
- start dividing again
- E.G lymphocytes in an immune response
6
Q
control of cell cycle
A
- checkpoints = control mechanism of cell cycle
- G1 : end of G1 phase before S.
- If cell is correct, DNA replication is triggered
- if not, enters resting state of G0
- G2 : end of G2 before mitotic phase.
- Cell checks DNA for errors
- if passed cell initiates molecular processes for beginning of mitosis
- Spindle assembly/metaphase checkpoint :
- point of mitosis where chromosomes attached to spindles
- have aligned
- mitosis can’t proceed until this checkpoint is passed.
7
Q
significance of mitosis
A
- when all daughter cells = identical
- during growth, replacement + repair of tissues
- necessary for asexual reproduction (genetically identical offspring from 1 parent)
8
Q
chromosomes : before mitosis
A
- DNA replicated before M occurs during interphase
- chromosomes converted into chromatids
- chromatids joined at centromere
- during interphase DNA combines with histones to form chromatin
9
Q
why do you keep chromatids togehtor during mitosis
A
- can be precisely manoeuvred
- segregated equally
10
Q
stages of mitosis
A
Prophase:
- chromosomes condense
- shorter + fatter
- centrioles move to opp ends of cell
- forms spindle fibres
- nucleolus disappears
- nuclear envelope breaks down
- chromosomes free in cytoplasm
Metaphase:
- chromosomes align on metaphase plate (middle)
- attached to spindle by centromere
- metaphase checkpoint checks chromosomes attached to spindle before mitosis continues
Anaphase:
- centromeres divide
- separates each pair of sister chromatids
- spindles contract
- chromatids pulled to opp ends, centromere first
- V shaped chromatids
Telophase:
- chromatids on opp poles on the spindle
- uncoil
- long + thin
- called chromosomes
- nuclear envelope forms around each chromosomes
- now 2 nuclei
Cytokinesis:
- cytoplasm divides
- 2 daughter cells = genetically identical
- normally begins in anaphase ends in telophase
11
Q
cytokinesis in animals
A
- in animals : cleavage furrow forms
- CSM pulled inwards by the cytoskeleton
- fuses around the middle
- forms 2 cells
12
Q
cytokinesis in plants
A
- vesicles from golgi align on metaphase plate
- vesicles fuse with each other + CSM
- cell divided into 2
- CW form along new membrane
13
Q
2 divisions in meiosis
A
meiosis I : reduction division
- pairs of homologous chromosomes separated into 2 cells
- each intermediate cell contains one full set of genes instead of 2
- haploid
meiosis II :
- pairs of chromatids are separated
- forms two more cells
- 4x haploid cells are produced
14
Q
meiosis I stages
A
Prophase I:
- chromosomes condense
- shorter + fatter
- homologous chromosomes pair = bivalents
- crossing over
- centrioles move to opp ends
- forms spindle fibres
- nuclear envelope breaks down
- nucleolus disappears
Metaphase I:
- homologous pairs line up on metaphase plate
- attach to spindle fibres
- independent assortment
Anaphase I:
- spindles contract
- separates homologous pairs
- chromosomes to opp poles
- section of DNA on ‘sister’ chromatids break off and re-join at the chiasmata
- forms recombinant chromatids
Telophase I
- nuclear envelope forms around each group of chromosomes
- chromosomes uncoil
- cytokinesis occurs
- two haploid cells
15
Q
meiosis II
A
Prophase 2:
- chromosomes condense
- visible (short + fat)
- nuclear envelope breaks down
- begins spindle formation
metaphase 2:
- chromosomes assemble on metaphase plate
- chromatids aren’t identical (bc of crossing over)
- independent assortment
- more genetic variation
Anaphase 2:
- chromatids of individual chromosomes pulled to opposite poles
telophase 2:
- chromosomes uncoil
- form chromatin
- nuclear envelope forms
- nucleolus becomes visible
- cytokinesis forms 4 daughter cells
- haploid bc reduction division
- genetically different bc of CO + IA
