Apoptosis

From The School of Biomedical Sciences Wiki
Jump to: navigation, search

Apoptosis (or programmed cell death) is one of the methods by which the cell cycle is regulated. It can be in response to many things, for example: DNA in the cell being badly damaged, removal of dangerous cells or controlling cell numbers. The process of apoptosis is activated by the p53 gene which starts a cascade of events that eventually leads to caspases in the cells being activated [1].  Any damage to mitochondria can cause cell death. The damaged mitochondria leak cytochrome C from between the two cell membranes, activating the caspases. These caspases can then cleave nuclear lamins, activate DNAase as well as cleave the cytoskeleton. Cleavage of the nuclear lamin by endonucleases leads to nuclear fragmentation. in addition, cleavage of the cytoskeleton, and cell to cell adhesion proteins by the same enzyme causes the apoptotic cell to round up and disengage from neighbouring cells[2]. The damaged cell is then engulfed by phagocytosis.

Apoptosis can be initiated other ways for example, in tadpoles a hormone is produced from the thyroid gland that causes apoptosis to occur in their tail when they are becoming an adult frog. This causes the cells in the tail to die and their tail disappears [3][4]. The presence of certain genes can also result in cells fate being directed towards cell death for example ced-9. Prescence of the gene resulted in life of the cell continuing whereas, lack of the gene resulted in programmed cell death.[5]

Cell death is a normal occurance in early development. Cells are made in abundance and the excess cells undergo apoptosis. For example, in the development of the nervous system apoptosis is common [6].

Apoptosis is a strict and critical program that occurs during embryonic and adult life in order to maintain the status quo of the cells, when cells do not recieve growth signals they then go through apoptosis. The proteins involved in apoptosis cleave the nuclear lamins, digest the DNA, cleave the cytoskeleton thus the cell is separated from the rest of the surrounding cells, then lastly phagocytosis of the dying cell occurs. when cell signalling goes wrong and apoptosis doesn't occur then this can lead to cancer, this is because cells work as a team [7].

Programmed cell death is the process by which the body removes unwanted cells. It happens to a large extent in development, for example programmed cell death occurs between your fingers during development so that your fingers are separate, if this does not occur it results in syndactyly which is where your fingers are still joined together.
Programmed cell death occurs by the cell receiving a specific signal, shrinking and condensing as the cytoskeleton collapses the nuclear envelope is degraded along with the DNA. The cell then forms apoptotic blebs which are vesicles containing parts of the cell. These are then engulfed by macrophages and digested.

Programmed cell death doesn't only apply to animals. Plants, too, undergo this process during development, in the senescence (ageing) of flowers and leaves. In addition, programmed cell death is utilised in the response to injury and infection. Unicellular organisms such as bacteria and yeast also undergo apoptosis[8].

This is not to be confused with cell necrosis which is accidental cell death [9].

References

  1. Becker W.Bertoni G.Hardin J.Kliensmith L.(2009)The world of the cell,7th edition,San Fransisco:Pearson. p590
  2. Alberts et al (2008) Molecular Biology of the Cell, 6th Edition, New York: Garland Science
  3. Alberts B.Johnson A.Lewis J.Raff M.Roberts K.Walter P.(2008) molecular biology of the cell,5th edition,New york:Garland science. p1119
  4. Alberts B.Johnson A.Lewis J.Raff M.Roberts K.Walter P.(2008) Molecular Biology of The Cell,5th edition,New york:Garland science. p1118
  5. E. M. Hedgecock., J. E. Sulston and J. N. Thomson (1983) - Mutations affecting programmed cell deaths in the nematode Caenorhabditis elegans – Science, volume 220: pages 1277–1279
  6. Marieb, Elaine N. (2004)Human Anatomy and Physiology, 6th edition, San Francisco, Pearson. p112
  7. Lodish Harvey, Berk Arnold, Kaiser A. Chris, Krieger Monty, Bretscher Anthony, Hidde Ploegh, Amon Angelika, Scott P. Matthew.,(2013) Molecular cell biology,7th edition, New York: W.H.Freeman and company.
  8. Alberts, B., Johnson, A., Lewis. J., Raff, M., Roberts K,, Walter, P. (2008) Molecular biology of the Cell, 5th edition, New York: Garland Science. pg 1115.
  9. Alberts, Johnson, Lewis, Raff, Roberts, Walter. (2008). Molecular biology of the cell (5th ed.). new york: garland science. page 1115- 1129



Personal tools
Namespaces
Variants
Actions
Navigation
Toolbox