1.6 CELL DIVISION Flashcards
Before Mitosis can occur
All the DNA in the nucleus must be replicated
= INTERPHASE
Role of mitosis
Each chromo is converted from single DNA M into 2 identical DNA M: chromatids
During mitosis, 1 chromatid passes to each daughter cell
Mitosis def
Mitosis is the division of the nucleus into 2 genetically identical daughter cells
Mitosis is a X process
CONTINUOUS process
4 phases –> PMAT
CYCLINS AND THE CONTROL OF THE CELL CYCLE
CYCLINS, group of proteins, bins to enzymes “cyclin-dependent kinases” which become active and attach phosphate groups to other proteins in the cell
The attachment triggers the other protein to become active/ carry out tasks specific to one cell cycle phase
4 main type of cyclin in human cells
Unless these CYCLINS reach threshold concentration, the cell does not progress to the next stage
INTERPHASE overview
Very active phase of the cell cycle with many processes occurring in the nucleus/ cytoplasm
DNA rep in the nucleus and protein synthesis in cytoplasm only happens here
Number of mitochondria in cytoplasm increases due to growth/ division of mitochondria
In plant cells n. of chromo increase too
INTERPHASE PHASES
G1: all content but chromosome is duplicated
Some cells never go beyond G1: never going to be divided so they don’t need to prepare for mitosis
They enter G0: temp or permanent
S PHASE: replicates all genetic material/ each chromo is duplicated so that after mitosis new cells have a complete set of genes
SUPERCOILING
Chromosomes condense by supercoiling
DNA is immensely long: 50 000 um
Human nuclei: <5 um diameter
Essential to pack chromo= condensation of chromo
1st stage of mitosis: repeated coiling of DNA M–> shorter/wider = SUPERCOILING
Histone proteins associated with DNA in eukaryotes + enzyme help
PROPHASE
SUPERCOILING: chromo become shorter/ wider repeatedly
Nucleolus breaks down
Microtubules grow from MTOC “microtubules organising centre” to form spindle shapers array: links cell poles
Nuclear membrane breaks down
METAPHASE
MicroT still grows and attached to centromeres on chromo
Spindle microT put under tension to test it attachment is correct by shortening microT at centromere
It attachment is correct, chromo remains on equator
ANAPHASE
Each centromere divides
Pairs of sister chromatid can separate
By shortening of Spindle microT that pulls them to separate polls
Mitosis produces 2 gen identical nuclei because sister chromatids are pulled to opposite poles
TELOPHASE
Chromatids have reached the poles and are now called chromosomes
At each pole chromo are pulled tight in groups near MTOC and nuclear membrane reforms around them
Chromo uncoils and nucleus is formed
By now cell has divided and 2 daughter cells enter interphase
Mitotic index
Number of cell in mitosis
Divided by
Total number of cells
TUMOUR FORMATION AND CANCER overview
Mutagens, oncogenes and metastasis are involved in the development of primary/ secondary tumours
Tumour?
Group of abnormal cells
Benign
Cells adhere to each other and don’t invade nearby tissue or move thus they are unlikely to cause harm
Malignant
Detached tumour cells which can develop into secondary tumours and lead to death
Carcinomas
Malignant tumours
Cancer
Disease due to malignant tumour
Cause of cancer
Carcinogens: chemical/ agents that cause gene mutation and eventually cancer (radiation)
Mutation
Random changes to base sequence of genes
Yet most genes don’t cause cancer if they mutate
Cancer causing genes
Oncogenes
In a normal cell oncogenes control the cell cycle and division
Thus a mutation of an oncogene= uncontrolled cell division= tumour
Tumour cell
Several mutations are needed
V. Small chances but because of large n. Of cells the chance
Of having a tumour in a lifetime is significant
Metastasis
Movement of 1 tumour to a 2 nd one
CYCLINS
Proteins that ensure tasks are done at the right time
Control when cell moves to the next stage of cycle
Cytokinesis
Occurs during mitosis and if different in plant and animal cells
Cell can divide after mitosis with 2 genetically identical nuclei
Cytokines in animal cells
Plasma membrane is pulled inward around equator of the cell to form cleavage furrow
Using ring of contractile protein: actin and myosin
When cleavage furrow reaches centre, the cell is pinched apart into 2 daughter cells
Cytokinesis in plant cells
Vesicles move to equator where they fuse together
–> forms cell plate in the middle: lamella which fuses with the cell wall
diving the cell into two distinct daughter cell
Daughter cells bring in cellulose to equator be exocytosis
