Apoptosis and Necrosis Flashcards
What is Apoptosis
Programmed Cell Death without the release of harmful products
What does apoptosis with mitosis allows
Continuous renewal of cells
What are the characteristics of apoptosis
- It is energy dependant
- Enzymatic digestion of nuclear/cytoplasmic contents
How is apoptosis different to necrosis
- Necrosis cell death is unintended caused by cellular injury
- Apoptosis suppresses inflammation and responds to necrosis
Why is defective apoptosis clinically significant
Allows for neoplasia like cancer cells living longer
Why is apoptosis important in AIDs
HIV proteins activate CD4 on T-helper lymphocytes causing apoptosis
cause immunodepleting and dysfunction
What are the inhibitors of apoptosis
Growth factors
Ex. cellular matrix
Sex steroids
Viral proteins
What are the inducers of apoptosis
Lack of Growth factor Loss of matrix attachment Glucocorticoids Free radicals Ionising radiation DNA damage Ligand bind at death receptors
What are the two pathways of apoptosis
Intrinsic
Extrinsic
What members of the BCL-2 family does the intrinsic apoptosis pathway use
BCL-2 inhibits the factors that induce apoptosis (no apoptosis)
Bax forms Bax-Bax dimers that enhance apoptosis stimuli (yes apoptosis)
What stimuli does the intrinsic factor respond to
Growth factors Biochemical stress (DNA damage)
What is the p53 gene
A protein that induces cell cycle arrest and initiates DNA damage repair
When is apoptosis activated by pro-apoptotic members of the Bcl-2 family
When DNA damage is too difficult to repair
How is the extrinsic apoptosis pathway induced
Ligand binding at Tumour Necrosis Factor Receptors on cell surface
What receptors act as death receptors
TNFR1
Fas (CD95)
What is the result of ligand binding
Promotes clustering of receptor molecules
Initiates signal transduction cascade = CASPASES activation
Lymphocyte elimination
What are CASPASES
Cell death enzymes
What happens when apoptosis is triggered
- Activation of initiator caspases
- Other pro-caspases cleaved
- Active caspases cause degradation of cytoskeletal framework and nuclear proteins
What is necrosis
Traumatic cell death which induces inflammation and repair
What is necrosis characterised by
Bioenergetic failure
Loss of plasma membrane integrity
How does necrosis induce inflammation and repair
Ruptured plasma membrane
Cell content spillage
Inflammatory response and repair
What happens to a cell during coagulative necrosis after ischaemia
Cell retains shape as protein coagulates but metabollic processes shut down
Tissue goes from firm to soft as macrophages digest (can cause ventricular rupture if the tissue is the myocardium)
Where does liquefactive necrosis occur
In the brain because
what is caseous necrosis
Cheese like structured tissue
Most likely Tuberculosis
