What is mitosis?
The nuclear division which produces two genetically identical daughter nuclei each containing the same number of chromosomes as the parents nucleus.
Where does mitosis occur?
In ALL the somatic cells (body cells)
What is mitosis?
- Growth
- Cell replacement/regeneration
- Repair of tissues
- Asexual reproduction
Where is the majority of the cell cycle?
Interphase (metabolic activity and growth)
What happens in G1, the first growth phase?
Protein synthesis, cytoplasm and number of organelles increase rapidly, growth of cell
What happens at S synthesis?
DNA replicated (DNA doubles), cells divide
What happens in G2, second growth phase?
Proteins necessary for cell division are synthesised. Energy stores increased.
What is interphase?
Period of growth and development. The cell grows and carries out normal cell activities, replicated all other organelles.
Where does DNA replication occur?
During interphase
What are the stages of mitosis?
Prophase
Metaphase
Anaphase
Telophase
What happens at prophase?
- Chromatin condenses (shortened and thickens) to become visible as long threads called chromosomes.
- Each chromosome is made from two genetically identical chromatids held together by a centromere.
- Nuclear membrane disappears.
- Nucleolus disappears
- Centrioles move to the poles (opposite sides of the nucleus) and start to form spindles.
What happens at metaphase?
- Chromosomes arrange at the equator of the spindle.
- Microtubules are attached to the centromeres at one end of the spindle and the centrioles at the other end.
- Microtubules of spindle attach to the centromere.
What happens at anaphase?
- The centromere divides in two
- Spindle fibres contract and pull the chromatids apart to the opposite poles, centromere first.
- Chromatids are now called daughter chromosomes
What happens at telophase?
- Daughter chromosomes reach the poles, they uncoil and lengthen to become chromatin.
- Nuclear membrane returns
- 2 new nuclei are formed
- Spindle fibres disintegrate
What is cytokinesis?
It’s the division of the rest of the cell (cytoplasm and organelles) after the nucleus divides.
In animal cells the cytoplasm pinches in.
In plant cells a cell plate forms.
What happens after mitosis and cytokinesis has been completed?
The cell will return to interphase where it continues to grow and perform regular cell activities.
Use a flow diagram to show the cell cycle?
Interphase –> Mitosis (PMAT) –> Cytokinesis
How do you calculate mitotic index?
number of cells in mitosis/ total n.o. visible cells in field of view x100
What is cancer and what is it caused by?
It’s caused by uncontrollable mitosis. The cancerous cells divide repeatedly by mitosis forming a tumour (a regular mass of cells). Cancers are thought to be initiated by gene mutations in either oncogenes or tumour suppressor genes which controls cell divisions.
