Genetic Body Plans and Apoptosis

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  • Created by: Megan
  • Created on: 07-03-14 20:37

Genetic Body Plans

Homeobox Genes - control the development of the body plan of orgnaisms, including the polarity and positioning of the organs

  • These genes switch a whole set of other genes on or off, affecting an organisms body plan
  • Found in clusters call Hox Clusters

Most animals have very similar body plans and homeobox genes - The genes are highly conserved (they have not evolved much)

They code for production of transcription factors - these can bind to certain sections of DNA and cause it to be transcribed

Thalidomide disrupted the homeobox genes in developeing foetuses, so arms and legs did nto develop properly

Drosophilia (Fruit Fly)

  • Maternal effect genes - determine embyro polarity
  • Segmentation genes - specify polarity of each segment
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Apoptosis

...programmed cell death involved in development (e.g. the tail of a tadpole falls off as it changes)

Metamorphosis - a major change in the structure of an organism as it changes from one stage of its life to the next

1) Cytoskeleton broken down by enzymes

2) THe cell shrinks, the membrane blebs and the nucleus starts to disintegrate - Chromatin condenses

3) Cell fragments are made with plasma membranes and contain organelles

4) Cell fragments are ingested and digestion by phagocytic cells e.g. WBCs

(Phagocytosis - the endocytosis of large solid molecules into a cell)

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Control of Apoptosis

...controlled by cell signalling through cytokines, hormones, nitric oxide and growth factors

Nitric oxide makes inner mitochondrial membranes more permeable to H+ ions - inducing apoptosis

Proteins are released into cytosol and bind to apoptosis inhibitor proteins

Apoptosis and Development

  • Causes clean cell death so no hydrolytic enzymes are released
  • cell components are reused via phagocytosis
  • Removes harmful or ineffective T lymphocytes - usually kill infected body cells

Rate of cell death should equal rate of mitosis - too much causes cell degeneration and too little causes tumours (both benign and cancerous)

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