The Cell Cycle
the cel cycle is the process that all body cells use to grow and dicide.
the cell cycle consists of a period of cell growth and DNA replication called INTERPHASE
and a period of cell divison called mitosis
mitosis only occupies a small percentage of the cell cycle.
most of the cell cycle is taken up by interphase, which is subdivided into G2, S and G1THE CELL CYCLE STARTS AND FINSHES AT MITOSIS
During interphase the cell carries out its normal functions, but also prepares to divide.
the cells DNA is unravelled and replicated to double its genetic content.
The organelles are also replicated so it has spare ones and the atp content is also increased to provide the energy for cell divison.
There are two types of cell divison.
mitosis and meosis. mitosis is the type of cell divison that occurs during the cell cycle
Its needed for GROWTH, REPAIR (of damaged tissues), and REPLACEMNT.
It consists of prophase metaphase anaphase telophase
A chromosome has tow chromatids which are joined together by the centromere
- Chromatids condense getting shorter and fatter
- Centrioles start moving to opposite ends of the cell and form the spindle fibres
- The nuclear envolope breaks down and the chromosomes lie free in the cytoplasm
2. Metaphase ( Middle)
- the chromosomes line up at the equator
- The spindle fibres from the centrioless attach to the cenromeres of the chromosomes
3. Anaphase (apart)
-the centromeres divide, seperating each pair of siter chromatids.
-spindles contract to opposite ends of cell
- chromatids reach opposite ends of spindle.
- chromatids uncoil and become long and thin again and are now called chromosomes
- A nuclear envolope forms around each group of chromosomes so there are now two nuclei
- Cytokinesis occurs:
the division of the cytoplasm. the cell membrane constricts, pinching the cell into two identical daughter cells. Mitosis is finished and the two daughter cells start interphase again
Mitosis in Plants
in plants mitosis is similar but there are some differences.
- IN PLANTS ONLY CELLS AT THE MERISTEMS CAN DIVIDE BY MITOSIS
- DURING PROPHASE IN PLANTS SPINDLES FORM WITHOUT CENTRIOLES
- CYTOKINESIS IS DIFFERENT BECAUSE PLANTS HAVE A CELL WALL-IT BEGINS IN THE CENTRE ( NOT THE EDGE AS AN ANIMAL CELL WOULD) WITH A CELL PLATE- this is a double membrane which secretes materials needed to make two cell walls. the cell wall starts to form at the centre and moves outwards.