cell and nuclear division. mitosis produces genetically identical cells used for growth, repair and...
TRANSCRIPT
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.