Cell cycle & Life Cycle

Mitosis follow interphase. Due to the accuracy of mitosis, every cell that now forms your body is an exact genetic copy of that first cell that was formed when the sperm fertilised the egg. Mitosis works to maintain genetic stability. Genetic stability is vital to health, any changes to the DNA whe copying and dividing the DNA in mitosis are mutations which could increased the risk of developing a tumour.

Roles of Mitosis

• Makes cells
• Creates genetically identical cells
• Replacement of cells which are genetically identical and therefore perform the same function
• Growth of tissues           
• Repair of tissues              
• Asexual reproduction

Mitosis is a hugely powerful process, with the potential to create 1000’s of ‘new’ cells in a period of days.  This power is very tightly controlled by the body, no cell can undergo mitosis without receiving a number of signals to check it is safe to divide and desired by the body.  When the systems and signals regulating mitosis breakdown mitosis goes on uncontrolled, this is cancer and the result is a tumour.

Most cells spend most (nearly all) of their time not dividing, instead going about their normal functions; heart cells beat, muscle cells contract, white blood cells fight infection etc.

This period of time outside Mitosis, when a cell is not dividing, is known as Interphase. Only when the cell gets the correct signals does it move from Interphase into Mitosis proper.

The preparations of a cell to undergo cell division/mitosis and cell division are known as the Cell Cycle, the majority of the cell cycle is spent in Interphase.

To prevent mistakes and mutations the cell can only progress through the cell cycle by passing particular checkpoints; if there is a problem the cell will pause in the cell cycle until it is fixed.  If the problem cannot be fixed then the cell will kill itself for the good of the body, preventing a tumour developing.  This is called apoptosis. Upon receiving the correct signals and passing all the checkpoints, the cell is ready to enter mitosis and undergo cell division.

• G1 ( growth phase 1 )- protien synthesis/ transcription/ formation of mRNA/ organelles replicate/ ATP required.
• S ( synthesis phase) DNA replication/ ATP required
• G2 ( growth phase 11) cell growth/ cell size increases

Prophase

• Chromosomes condense/ become visable
• Consist of 2 genetically identical sister chromatids
• Joined by centromere
• Centrioles move to opposite poles
• Centrioles form spindle fibres

Metaphase

• Chromosomes align at equator
• Attatch to spindle fibres by centromere

Anaphase

• Centromeres split
• sister chromatids seperate 
• Move to opposite poles by shortening of spindle fibres

Telophase

• Chromosomes uncoil
• Nuclear envelope reforms

Cytokinesis

• cytoplasm constricts
• Two new cells are formed