explain the need for the tight control of mitotic cell cycle
controlled by G1, G2, M checkpoints; determine if cell cycle can proceed >
req of each checkpoint must be met b4 cells -> next stage(DNA repn is accurate/bring about DNA repair mechanisms if req) >
prevent dysregulation of checkpoints of cell division, prevents excessive CCP & UCD which leads to TF & possibly cancer >
tight control needed for normal cell division, cell development OR prevent cells w/ damaged DNA from continuing cell cycle
describe behaviour of chromosomes, nuclear envelope, cell surface membrane, centrioles during mitosis
P
chromatin condenses, form chromosomes >
2 pairs of centrioles move opp poles of cell, SFs formed >
NE disintegrates, fragments into NM vesicles
M
2 pairs of centrioles positioned @ opp poles of cell >
KSFs pull on centromeres, arrange chromosomes in single row on M plate
A
SF attached to centromere shorten & contract, pulls SCs to opp poles of cell >
centromeres divide, SCs separate @ centromere >
each SC becomes DC
T
DC pulled by SF attached to centromere reach opp poles of cell >
chromosomes uncoil, lengthen & become indistinct to form chromatin again >
SFs disintegrate >
NM vesicles bind to chromosomes & fuse tgt, NE reforms around chromatin in daughter cell
describe events that occur during mitotic cell cycle
Interphase(G1,S,G2 checkpoints)
longest phase of cell cycle, period of intense synthesis of cellular materials, growth >
nucleic acids, proteins, carbohydrates synthesised for own growth >
SCDR occurs @ S phase, amount of DNA x2, chromosome no. same >
each chromosome consists 2 genetically identical SCs held tgt @ centromere >
each SC exact copy of chromosome before replication >
chromatin remains uncoiled, decondensed
Mitosis
replicated copies of each chromosome, associated proteins precisely divided, enclosed into 2 daughter nuclei in PMAT
Cytokinesis
furrow develops in animal cell/cell plate formation in plant cell; division of cytoplasmic content, produce 2 genetically identical daughter cells
explain significance of mitotic cell cycle
growth
enables multicellular organism grow, develop from 1 single cell;fertilised egg >
if tissue must enlarge in growth, new cells must be genetically identical to existing cells; new cell reproduction achieved by mitosis
repair
after organism fully-grown, cell division continues to function in renewal, repair of tissues >
damaged, worn-out cells replaced by exact copies to return tissue to former condition; achieved via mitosis
asexual reproduction
production of new individuals of species by 1 parent organism >
most organisms propagated by AR, results in clones so that species can colonise particular stable, well-adapted habitat within shortest time period
how mitosis produce genetically identical cells/ how mitosis maintains genetic stability in organism?
SCDR occurs during S phase of interphase, form SCs genetically identical to parent DNA >
during M each chromosome arranged on M plate; each SC of chromosome face opp poles of cell >
separation of SCs during A lead to formation of genetically identical DC, ensures even distribution of DC into daughter nuclei; forms 2 genetically identical nuclei in daughter cells >
no crossing over/exchange of segments b/w non-SCs of HCs; no genetic recombination/variation >
ensures production of genetically identical cells
describe chromosome structure @ start of mitosis
SCDR occurs, S phase of interphase, produce 2 identical DNA molecules >
each chromosome consists 2 identical SCs held tgt @ centromere >
@ start of mitosis, chromosome exists uncoiled, decondensed chromatin >
DNA molecule wind around histone octamer -> nucleosome >
nucleosomes connected by linker DNA, associates w/ H1 histones -> nucleohistone complex >
H1 histone interaction results in further coiling into 30nm chromatin fibre >
30nm chromatin fibre forms looped domains attached to scaffolding proteins
-> 300nm chromatin fibre >
centromere is constricted region on chromosome made up of non-coding DNA of series of tandem repeat seq >
no. of centromere-associated proteins bind to centromeric DNA -> kinetochore
outline role of centromeres
hold SCs tgt, divide allowing separation of SCs into DC >
centromeric DNA essential for proper alignment, separation of SCs/HCs to opp poles of cell during nuclear division >
ensure proper segregation of chromosomes by being site on chromosome where kinetochore assembles, SFs from centrioles attach during nuclear division >
consists of specific non-coding DNA made up of series of tandem repeat seq which no. of centromere-associated proteins bind, forms kinetochore
outline role of centrioles
act as MTOC in nuclear division >
2 pairs of centrioles move to opp poles of cell, determines polarity of cell >
centrioles produce SFs @ poles towards equator of cell, organise synthesis of SFs, leads to separation of chromatids during cell division
outline role of spindle fibres
guide movement of chromosomes during nuclear division; align chromosomes @ M plate, move chromatids/chromosomes to opp poles of cell during anaphase >
ensure each daughter cell receives exact no. of chromosomes during cell division