Mitosis

Mitosis is the devision if a cell which results in each of the daughter cells having an exact copy of the DNA of the parent cell. 

Mitosis is always preceeded by a period during which the cell isnt deviding.

Period of conciderable activity that includes a very important event the replication of DNA . The two two copies of DNA after the replication the DNA remain joined at the centrometre.

The chromosomes first become visable, initially as long thin threads, which sortern and thicken. 

Animals cells contain two cylindrical organelles called centrioles, each of which moves to opposite poles of the cell. From each of the centrioles spindle fibers develop which span the cell from pole to pole. 

Collectively spindle fibers are called spindle apparatus . 

As plant cells lack centrioles, but do develop spindle apparatus, clearly showing that centrioles aren't essential to spindle fiber formation. 

The nucleolus disappears and the nuclear envelop breaks down , leaving chromosomes free in the cytoplasm in the cell. 

These are chromosomes are drawn towards the equator of the cell. 

Chromosomes are seen to be made up of two chromotids. 

Each chromoatid is an exact copy of the DNA from the parent  cell joined by the centromere. 

Chromosomes are pulled along the spindle apparatus of the cell and arraged across the equator of the cell. 

During anaphase, the centroles divied into two and the spindle fibers pull the individual chromatids apart. 

The chromatids move rapidly to thir respective ends of the cell and now refer to them as chromosomes. 

The energy for this process is provided by mitochondria. 

Chromosomes reach their respective poles and become longer and thinne, finally dissapearing altogether, leaving only wide spead chromatin

The spindle fibers disintergrate and nuclear envelop and nucleoulus reform. 

Finally cytoplasm divides via the process of cytokinesis

Cell devision in prokaryotci cells occurs by BINARY FISSION 

• Circular DNA molecuel replicates and both copies attach to cell membrane
• Plasmids also replicate
• The cell membrane begins to grow between the two DNA molevcuels and begins to pinch inwards, dividing the cytoplasm in two. 
• A new cell wall forms between the molecuels of DNA, dividing into two identical daughter cells with a single copy of the plasmids

Viruses are non-living, they can't undergo cell devision.

Instead they replicate by attaching to their host cell with the attachment proteins on their surface 

• They inject their nucleic acid into the host cell. The injected host information on the injected viral nucleic acid then provides the instructions for the host cells metabolic process to start producing the viral components:nucleic acid, enzymes, structural proteins and then assembled into new viruses