4.2 Mitosis Flashcards
Why do all multicellular eukaryotic organisms require a continuous supply of new cells? (3)
For
- Growth (we need more cells as we grow)
- Development (we need new cell types as we develop new tissues)
- Repair (we need to replace the cells that we lose each day)
What is a cell cycle?
The series if steps that take place as a cell grows then divides.
What happens in the interphase stage of the cell cycle? (3)
1) Before it divides, the cell has to grow and increase the amount of subcellular structures such as mitochondria and ribosomes.
2) In a cell that’s not dividing, the DNA is all spread out in long strings. However when it is preparing for division, the DNA condenses into chromosomes (coiled up packets of DNA).
3) It then duplicates it’s DNA so there’s one copy for each new cell. The DNA is copied and forms X-shaped chromosomes. Each ‘arm’ of the chromosome is an exact copy of the other
What happens in the mitosis stage of the cell cycle? (3)
Once its contents and the DNA have been copied, the cell is ready for mitosis…
4) The chromosomes line up at the centre of the cell and cell fibres from either side of the cell attach to their respective half of each chromosome and pull them apart. The two arms of each chromosomes go to opposite ends of the cell. We call these sides “poles”.
5) Membranes form around each of the sets of chromosomes. These become the nuclei of the two new cells - the nucleus has divided. This is called division or cytokinesis.
6) Lastly, the cytoplasm and cell membrane divide.
The cell has now produced two new daughter cells. The daughter cells contain exactly the same chromosomes (DNA) - they’re genetically identical. They’re also genetically identical to the parent cell.
Brief steps of the cell cycle (5)
1) Cellular growth - the cell gets larger and produces more sub-cellular structures, such as mitochondria and ribosomes.
2) DNA replication - chromosomes duplicate, so that each consists of two arms (copies).
3) More cell growth.
4) Mitosis - the DNA divides into two.
5) Cytokinesis - the cell divides into two.
How many pairs of chromosomes do most human cells have?
23
What do we commonly call the cells produced by mitosis?
Daughter cells
What is the formula of finding how many cells there will be after multiple divisions of a cell by mitosis?
Number of cells = 2 to the power of n, where ‘n’ is the number of divisions by mitosis.
How can a tumour form by mitosis?
The rate at which cells divide by mitosis is controlled by the cells’ genes. If there’s a change in one of the genes that controls cell division, a cell may start dividing uncontrollably. This can result in a mass of abnormal cells called a tumour.
