Apoptosis - Programmed cell death
Programmed cell death in multicellular organisms, which keeps Mitosis in check.
Apoptosis is important for plant and animal tissue development = the rapid division of cells is balanaced by the death of cells via Apoptosis. Cell signalling plays a vital role in the maintainence of the correct balanace.
Different tissues use different signals to induce Apoptosis: cytokines (immune system), hormones, growth factors and nitric oxide (makes inner mitochondrial membranes more permeable to H+ ions).
- Cells undergo a reduction in size and cellular components break down
- Enzymes break down the cell cytoskeleton and blebs form as the cell surface membrane changes
- The cytoplasm condenses, the organelles become tightly packed, mitochondria break down
- Chromatin condenses, the nuclear envelope breaks and the DNA breaks into fragments
- Phospholipids on the surface of the membrane act as receptor sites for the phagocytes.
- The cell breaks into vesicles, which are engulfed by endocytosis by phagocytes
- Cell components = reused. No hydrolytic enzymes are released into the surrounding tissue.
Why do cells need to be destroyed?
- Ensure proper development e.g. Webbed fingers or the separation of toes - Menstruation = removal of tissue from uterus - Cells could be damaged = need to be removed - Cells could be infected = need to be removed - Tumor can form if there is not enough Apoptosis.