Cell Division Flashcards
1
Q
Cell Cycle (Interphase)
A
- CHROMOSOMES CANNOT BE SEEN AS DISTINCT STRUCTURES IN NUCLEUS
- only dark regions (chromatin) can be seen
- chromosomes are loose so DNA can be accessible for transcription & translation
1) G1
- transcription & translation takes place
- organelles are replicated
- cell size increases
- G0 = cell exits cycle due to damaged DNA, differentiation or just temporarily
2) S PHASE
- DNA synthesis
- chromosomes are replicated
3) G2
- cell size further increases
- transcription & translation continues
- replaces energy stores used up in ‘S PHASE’
- repairs damaged chromosomes
2
Q
Checkpoints
A
- corrects errors in DNA for cycle to continue
- cell leaves cycle if checkpoint is failed
G1 CHECKPOINT
- cell size/nutrients
- DNA damage
AFTER G2
- cell size
- DNA (tertiary structure) damage
METAPHASE CHECK
- checks for attachment of chromosomes to spindle and the size of cell
3
Q
Mitosis
A
- divides nucleus of each daughter cell !
- diploid cells are chromosomes in pairs
- 2 genetically identical daughter cells
- used for ‘growth & repair’ or ‘asexual reproduction’
- 2 replicated chromosomes = ‘sister chromatids’
- s. chromatids are joined together by ‘centromere’
4
Q
PROPHASE
A
- chromosomes condense (visable)
- nuclear env. breaks down into vesicles
- each chromosome has 2 s. chromatids
- centroMERES move to opposite ends of nucleus and form poles
- proteins for spindle fibres
5
Q
METAPHASE
A
- centroSOMES reach a pole
- spindle fibre is made from m. tubules
- chromosomes line-up across equator as they’re attracted by centroMERES
6
Q
ANAPHASE
A
- each chromosome splits (1 chromatid)
- s. fibres shorten so…
- chromatids are pulled to opposite poles
7
Q
TELOPHASE
A
- nuclear envelope reforms
- chromatids uncoil (decondense) back to ‘chromatin state’
- each chromatid contains one DNA molecule
- spindle fibres breakdown
8
Q
CYTOKINESIS
A
- central plasma membrane is pulled inwards by cytoskeleton
- cell pinches at the middle & membrane’s FUSE
- cytoplasm full divides
- creates 2 new genetically identical daughter cells
9
Q
Mitosis (PLANT CELLS)
A
- no centrioles in process
- vesicles from Golgi A. move to the equator and fuse forming a ‘cell plate’
- ^ aka a ‘contractile ring’
- cell plate forms new cellulose cell wall
& cell splits into 2
10
Q
Meiosis
A
- known as ‘reductionist division’
- produces 4 genetically different haploid gametes (sex cells)
- gametes fuse together so the zygote becomes the diploid cell
11
Q
Homologous Chromosomes (HC)
A
- have exactly the same genes
- genes are in the same loci
- different alleles of the same gene can be inherited e.g. blood group
12
Q
Prophase 1 & 2
A
- HC condense
- nuclear envelope disintegrates
- spindle formation
- (1) crossing-over of chromatids form bivalents in HC
12
Q
Metaphase 1 & 2
A
- similar in mitosis
- ^ however, bivalents line up on the equator randomly & independently
- ^ known as ‘independent assortment’ which creates genetic variation
- maternal/paternal chromosomes can face either way (inc. their alleles) creating more variation
- (2) individual unidentical chromosomes line up
- ^ independent assortment happens again
13
Q
Anaphase 1 & 2
A
- (1) chromatids in HC stay joined to centromere when pulled to opposite poles (unlike in mitosis)
- sections of sister chromatids break off and re-join from ‘chiasmata’
- ^ DNA exchanges, leading to more genetic variation
- sister chromatids are no longer identical
- (2) unidentical sister chromatids separate like in mitosis
14
Q
Telophase and Cytokinesis 1 & 2
A
- (1) same in mitosis ; 2 chromatids in each chromosome
- (2) 1 chromatid from each parent in all 4 daughter cells
- ^ haploids are created
