Cell and Nuclear Division

Mitosis

• Produces genetically identical cells• Used for growth, repair and asexual

reproduction

Cell cycle

Interphase

• Growth• DNA replication

Mitosis phases

• Prophase• Metaphase• Anaphase• Telophase• Cytokinesis

Prophase

• Nuclear membrane starts to break down

• Centrioles replicate and start to move to opposite poles

• Chromotids condense

Metaphase

• Chromatids move to the equator

• Line up randomly• Centrioles

produce spindle fibres

Anaphase

• Spindle fibres connect to centromere and start to contract

• Chromosomes move towards the poles

Telophase

• Chromosomes start to unwind

• Nuclear membrane starts to reform

Cytokinesis

• Cell divides into two by infolding of the plasma membrane in animal cells and formation of new cell wall and membrane in plant cells

Cancer

• When control mechanisms break down the cell starts to divide uncontrollably

• There is rapid mitosis and a tumour forms that has no function.

• Benign tumours do not spread from their point of origin

• Malignant tumours spread through the body and invade other tissues. This is called metastasis.

Mutagen or Carcinogen?

A mutagen is any factor that causes a mutation in a gene, and so is called a mutagenic factor.

Most mutations caused in this way cause the cell to self-destruct, or to be destroyed by the immune system.

• Carcinogens – cancer causing factors, and so therefore are referred to as Carcinogenic factors.

• They cause mutations in the genetic make up of a cell, which are not immediately fatal or recognized by the immune system.

• Examples of these factors are:– Ionising radiation (radiation, UV, X-rays)– Chemicals like tar– Viral infections– Hereditory predisposition

Meiosis

• Diploid cell – contains two complete sets of chromosomes (2n)

• Haploid – contains one complete set of chromosomes (n)

• Sexual reproduction requires a reduction cell division so that two haploid nuclei can join to make a diploid zygote.