Mechanisms Of Disease 2 Flashcards
What is the function of necrosis?
Removes damaged cells from a organism
Failure to do so may lead to chronic inflammation (necrosis induces acute inflammation to clear cell debris via phagocytosis)
What causes necrosis?
Usually a lack of blood supply (injury, infection, cancer, infarction, inflammation)
This decreases the ppO2 in the affected area and a decrease in the pH
Describe the process of necrosis step by step.
- Result of an injurious agent or event
- Initial events are reversible, later ones die
- Lack of oxygen prevents ATP production
- As ATP require for ion pumps to work - cells swell due to a influx of water
- Lysosomes rupture; enzymes released degrade other organelles and nuclear material haphazardly
- Cellular debris released, triggering inflammation
What nuclear changes occur in NECROSIS under a microscope?
Nuclear changes:
- chromatin condensation/shrink
- fragmentation of nucleus
- dissolution of chromatin by DNAse
What cytoplasmic changes occur during NECROSIS under a microscope?
- opacification: protein denaturation and aggregation - turns white
- complete digestion of cells by enzymes causing cell to liquify
What biochemical changes occur during NECROSIS under a microscope?
- release of enzymes (creatine kinase and lactate dehydrogenase)
- release of proteins (myoglobin)
What is the function of apoptosis?
Selective process for the deletion of superfluous, infected or transformed cells
Involved in:
- Embryogenesis
- Metamorphosis
- Normal tissue turn over
Describe the step by step process of apoptosis
- Programmed cell death of one or few cells
- Events are irreversible and is energy dependent (requires ATP)
- Cells shrink as the cytoskeleton is dissembled
- Orderly packaging of organelles and nuclear fragments into membrane bound vesicles
- New molecules are expressed on vesicle membranes that stimulate phagocytosis without causing a inflammatory response
What cytoplasmic changes occur during APOPTOSIS under a microscope?
- shrinkage of cell + organelles packaged into membrane vesicles.
- cell fragmentation + membrane bound vesicles bud off
- phagocytosis of cell fragments by adjacent cells and macrophages
- minimal leakage of cytosolic components so no inflammation
What nuclear changes occur during APOPTOSIS under a microscope?
- nuclear chromatin condenses on the nuclear membrane
- DNA cleavage
What biochemical changes occur during APOPTOSIS under a microscope?
- expression of charged sugar molecules on the outer surface of membrane of vesicles
- protein cleavage l protease, caspases
What is metamorphosis?
Tadpoles tail is lost by apoptosis
What is interdigital web loss?
The webs between paws are lost in mouse paw development
Also occurs in humans (syndactyly)
What are the two types of apoptosis?
Intrinsic
- viral infection (on,y once virus is in cell)
- Inhibition of protein synthesis
- DNA damage
Extrinsic
- withdrawal of survival, factors
- Extracellular signals
- T cell or NK
RELATIVE TO THE CELL
What are capsases?
The point of convergence for causes of apoptosis.
They are cysteine proteases.
Arrange themselves to form a activation cascade, where one cleaves and activates the next.
What are the different type of caspases?
Initiator caspases
- 8,9
- few molecules
Effector caspases
- 1,3,6,7
- more and more molecules
What occurs during a caspase cascade?
- A inactive procaspase Y is cleaved by active caspase X where a pro domain (NH2) is removed
- Caspase Y is now active and consists of a small and large subunit
- Active caspase Y can activate other caspases
What is the function of the caspase cascade?
Cleavage of cytosolic proteins
Cleavage of nuclear lamina (nuclear membrane)
What is the effect of caspase activation?
Leads to characteristic morphological changes:
- shrinkage
- chromatin condensation
- DNA fragmentation
- plasma membrane blabbing
How are initiator caspases activated?
Activate themselves when in close proximity
How is extrinsic apoptosis induced?
By ligand binding to receptors, causing receptor multierisation, which leads to the activation of the initiation caspase
What are the molecules involved in the ligand induced multimerisation?
Outside cell/on surface:
- receptor
- ligand
Inside cell:
- death adaptor
- procapase-8
What is the structure of the receptor?
Ligand binding domain
DEATH DOMAIN
What is the structure of the death adaptor?
DEATH DOMAIN
DEATH EFFECTOR DOMAIN
What is the structure of the procaspase-8?
DEATH EFFECTOR DOMAIN
protease domain
Describe ligand induced multimerisation using TNF (tumour necrosis factor)
- TNF binds to TNFR
- Brings together per the death domains of the receptors in close proximity which creates a environment for other proteins containing these domains is favoured.
- Death adapter protein (FADD) associates/dimerises with the receptors death domain
- This leads to a high concentration of death effector proteins, inducing a environment for other molecules with the death effector domain to bind
- Procaspase-8 then binds/dimerises with FADD
- A death inducing signalling complex (DISC) is formed
- Procaspase-8 is then released through auto proteolysis and can induce a caspase cascade in the cell
How is intrinsic apoptosis induced?
By cytochrome c released from mitochondria.
(One form of extrinsic apoptosis can also use cytochrome C)
What is cytochrome c?
Mitochondrial matrix protein
Released in response to oxidative stress by a “permeability transition”
What molecules are induced in cytochrome c induced apoptosis?
Cytochrome
APAF-1
Procaspase-9
What is the structure of APAF-1?
- cytochrome binding site
- APAF domain
- CASPASE RECRUITING DOMAIN
What is the structure of procaspase-9?
- CASPASE RECRUITING DOMAIN
- protease domain
Describe cytochrome c induced apoptosis.
- Cytochrome binds to APAF-1
- Creates a environment of high caspase recruitment domain affinity
- Procaspase-9 binds to APAF-1 and a Apostosome forms
- Auto proteolysis activates caspase 9
How is the real ease of cytochrome c from the mitochondria regulated?
By a pore made of BCL-2 family of proteins
Some are not membrane proteins
All have a BH3 domain used to form dimers
What are the 2 types of BCL-2 proteins and they’re function?
Pro-apoptotic:
- facilitate cytochrome c release
Anti-apoptotic:
- repress cytochrome c release
Describe the example of BAX and BCL-2 and BAD
- BAX only - cytochrome c is released
- BAX and BCL-2 - cytochrome c remains in mitochondria (BCL-2 is not a membrane protein and blocks the use of the BAX channel)
- BAX and BCL-2 and BAD - cytochrome c can leave mitochondria as BAD has a greater affinity for BCL-2 it displaces it and prevents it from binding to BAX
How does TP53 regulate BCL-2?
- Transcription is driven by TP53
- Increased BAX production
- More BAX inserted into membrane
- Increased permiability of cytochrome c
5. Cytochrome c leaves mitochondria and cell death occurs
How do growth factors regulate BCL-2 by phsophorylation?
- Growth factors from survival signals activate Akt/PKB which phosphorylated BAD
- BAD cannot bind to BCL-2
- Cell survives ac cytochrome c cannot leave the mitochondria
Why is necrosis usually more damaging then apoptosis?
Apoptosis is a controlled process where the cell contents are packaged in membrane and not released. This means the surrounding tissue is protected from damaging molecules such as proteases.
Explain why lack of oxygen causes cells to swell as part of necrosis
Lack of oxygen prevents oxidative phosphorylation
Less ATP production
Lack of ATP prevents normal function of sodium channels
Leads to a altered ionic balance across the membrane leading to the entry of water into the cytoplasm.
