Cell Damage And Cell Death Flashcards
(44 cards)
1
Q
List the functions of necrosis
A
- Removes damaged cells from an organism
- Failure to do so may lead to chronic inflammation
- Necrosis causes acute inflammation to clear cell debris via phagocytosis
2
Q
List the causes of necrosis
A
- Usually a lack of blood supply
- Injury
- Infection
- Cancer
- Infarction
- Inflammation
3
Q
Describe the causes of necrosis graph
A
- Graph with distance from vessel (ùm) on X axis and pH on Y axis. On the right hand side, there’s partial pressure of O2
- Going from 0 to 100 um, there’s a dramatic drop in PO2 from 12 to 4
- From 100 to 200 um, there’s 0 PO2 so an anoxic environment (no O2), there’s a decrease in pH
- As you move away from the blood vessel, the environment becomes more acidic
4
Q
Describe the process of necrosis in steps
A
- Result of an injurious agent or event
- Initial events are reversible, later ones are not
- Lack of oxygen prevents ATP production
- Cell swell due to influx of water (ATP is required for ion pumps to work)
- Lysosomes rupture; enzymes degrade other organelles and nuclear material hapzardly
- Cellular debris released, triggering inflammation
5
Q
How does necrosis appear under a microscope?
A
- Can be divided into 2 groups
- Nuclear changes
- Cytoplasmic changes
6
Q
Describe the nuclear changes of Necrosis appearance under a microscope
A
- Chromatin condenses and shrinks
- Nucleus begins to fragment
- Dissolution of the chromatin by DNAse
7
Q
Describe the Cytoplasmic changes of Necrosis appearance under a microscope
A
- Opacification: Protein denaturation & aggregation
- Complete digestion of cells by enzymes causing cells to liquify (liquefactive necrosis)
8
Q
What are the biochemical changes that occur from necrosis?
A
- Release of enzymes such as creatine kinase or lactate dehydrogenase
- Release of other proteins such as myoglobin
- These biochemical changes are useful in the clinic to measure the extent of tissue damage
9
Q
Check diagram for the kidney stains of normal or necrotic cells
A
10
Q
What are the functions of apoptosis?
A
- Selective process for the deletion of superfluous, infected or transformed cells
- Involved in:
- Embryogenesis
- Metamorphosis
- Normal tissue turnover
- Endocrine dependent tissue atrophy
- A variety of pathological conditions
11
Q
Describe the process of apoptosis in steps
A
- Programmed cell death of one or a few cells
- Events are irreversible and energy (ATP) dependent
- Cells shrink as the cytoskeleton is desassembled
- Orderly packaging of organelles and nuclear fragments into membrane bound vesicles
- New molecules are expressed on vesicles membranes that stimulate phagocytosis without an inflammatory response
12
Q
Describe the cytoplasmic changes of Apoptosis appearance under a microscope
A
- Cytoplasmic changes
- Shrinkage of cell. Organelles packaged into membrane vesicles
- Cell fragmentation. Membrane bound vesicles bud off
- Phagocytosis of cell fragments by macrophages and adjacent cells
- No leakage of cytotoxic components
13
Q
What are the 2 types of electron microscopy images produced for apoptosis?
A
- Transmission EM: Produces a slice through the cell, 2D section, not much cytoplasm but mainly nucleus
- Scanning EM: Shows the surface of the membrane
14
Q
Describe the nuclear changes of apoptosis appearance under a microscope
A
- Nuclear changes
- Nuclear chromatin condenses on nuclear membrane
- DNA cleavage
15
Q
Describe the Biochemical changes of apoptosis appearance under a microscope
A
- Biochemical changes
- Expression of charged sugar molecules on outer surface of cell membranes (recognised by macrophages to enhance phagocytosis)
- Protein cleavage by proteases, caspases
16
Q
Give an example of metamorphosis
A
- Tadpole’s tail lost by apoptosis
- At first the tadpole has a long tail
- But once it starts to grow properly, it loses this tail by apoptosis
17
Q
Describe interdigital web loss
A
- In certain animals, the fingers are a lot more attached to eachother
- Apoptosis then occurs to separate the fingers a lot more
- E.g. Mouse paw development
18
Q
The cell constantly undergoes a balance between life or death
What are the balancing factors of a cell between survival and apoptosis?
A
- Survival factors: Growth factors, Cytokines, cell-cell or cell-matrix contacts
- Apoptosis factors: Lack of growth factors, DNA damaging agents, Death domain ligands, Disruption of cell-cell or cell-matrix contacts
19
Q
What are the 2 types of apoptosis?
A
- Intrinsic
- Extrinsic
20
Q
Describe the intrinsic features of apoptosis
A
- DNA damage: p53 dependent pathway
- Interruption of cell cycle
- Inhibition of protein synthesis
- Viral infection
- Change in redox state
21
Q
Describe the extrinsic features of apoptosis
A
- Withdrawal of survival factors
- Extracellular signals
- T cell or NK (natural killer)
22
Q
Describe caspases
A
- Caspases are the point of convergence for causes of apoptosis
- For e.g. Extrinsic causes + intrinsic causes -> caspases -> apoptosis
- Caspases are cysteine proteases
- Caspases form an activation cascade, where one cleaves and activates the next (analogues to kinase cascades)
- Caspase - activates caspase Y
23
Q
Describe the caspase cascade
A
- At the top there’s an initiator caspase which has a few molecules
- This activates downstream Caspases
- Which in turn will activate more downstream Caspases
- These downstream Caspases have additional Caspases known as cleavage of nuclear lamin
- These downstreams with additional Caspases are known as effector Caspases
24
Q
What happens when you have large amounts of many substrates?
A
- Hundreds of substances for activated Caspases
- Substrates fall into most classes of important genes
- Death by a thousand cuts occur
25
What is the effect of caspase activation?
- Caspase activation leads to characteristic morphological changes, such as shrinkage, chromatin condensation, DNA fragmentation and plasma membrane blebbing
26
How is the initiator caspase activated?
- Initiator Caspases activate themselves when in close proximity
- Activation, therefore means bringing initiator Caspases together
27
Describe extrinsic apoptosis
- Induced by ligand binding to receptor causing a receptor diner or (multimer) isation
28
Describe the ligand induced multimerisation: the players
- You have a ligand which will bind to its transmembrane receptor on the cell membrane
- You then have an intermediate protein which can be classified as a group of death adaptive proteins
- You then finally have the initiator caspase which is the procaspase-8
29
What does the ligand receptor and the death adaptor share in common?
What does the death adaptor and procaspase-8 share in common?
- Receptor and death adaptor share the death domain
- Death adaptor and procaspase-8 share the death effector domain
- These shared domains usually allow the proteins to bind together
30
Give a specific example of these binding domain stuff
- There’s the tumour necrosis factor signal
- There’s also a TNFR (tumour necrosis factor receptor which is above the membrane
- The death adaptor protein (4 in total) is know as the FADD (Fas associated protein with death domain)
- This creates an environment of high death adaptor concentration
- The death adaptor then recruits procaspase 8
- When you add all these together, it creates a death inducing signalling complex
- When bought into close proximity, autoproteolysis occurs which is how these Caspases become active
31
Describe the intrinsic form of apoptosis
- Induced by cytochrome C released from mitochondria
- Note: Growth factor withdrawal (extrinsic apoptosis) is an exception that uses cytochrome C
32
What is Cytochrome C?
- Mitochondrial matrix protein
- Known for many years to be released in response to oxidative stress by a “permanent transition”
- Any inducers of the permanent transition also eventually induce apoptosis
33
Describe the cytochrome C induced apoptosis in a schematic way in the intrinsic pathway**
- In this case, there’s a similar type of death adaptor protein called APAF 1 (apoptotic protease activating factor)
- There is also the initiator caspase which is procaspase 9 in this case
- The common domain shared between APAF 1 and procaspase 9 is the caspase recruitment domain
34
What happens when cytochrome c is released? In relation to the last card
- Cytochrome C is released from mitochondria
- It binds to its binding domain in APAF 1 bringing these molecules together
- Dimerisation, multimerisation, recruitment of procaspase 9 come together and is referred to as an apoptosome
- The proteolytic domain of procaspase 9 is in close proximity allowing it to target itself, cleave itself
- Resulting in active caspase 9 which can enter the cytoplasm and trigger a caspase cascade
35
How is the release of cytochrome C from the mitochondria regulated?
- Through a family of proteins called the BCL-2 family
- BCL-2 is both a member of the family and the family itself
36
What does the BCL-2 proteins form?
- They form the permeability pore through which cytochrome C can be released
- BCL-2 proteins can be pro or anti apoptotic
37
Give some examples of anti apoptotic and pro apoptotic proteins
- Anti apoptotic: Repress cytochrome C release (bcl-2, bcl-XL)
- Pro-apoptotic: Facilitate cytochrome C release (Bax, Bad, Bid, others)
- Some are not membrane proteins
- All have a BH3 domain used to form dimers
38
Give an example of how BAX is expressed
1. BAX is pro apoptotic
2. Creates a pore
3. Outgoes cytochrome C is released through the Bax membrane
4. Leading to cell death
39
Give an example of how BAX + BCL-2 is expressed
1. BCL 2 is anti apoptotic, not a membrane protein
2. It binds to Bax and acts like a gate
3. It closes the door and stops cytochrome C being released from mitochondria
4. Promotes survival
40
Give an example of how BAX + BCL-2 + BAD is expressed
1. BAD is a pro apoptotic protein that binds very strongly to BCL-2. More strongly than BCL-2 binds to Bax
2. BAD displaces all the BCL-2 from the pore
3. This allows the Cytochrome C to be released again
41
If the BCL-2 family proteins regulate the cytochrome C release from mitochondria, what regulates BCL-2 proteins?
Mainly down to gene expression and Post transcriptional modification
42
How does transcription factor TP-53 activated by DNA damage and various other things activate apoptosis?
- If there’s DNA damage, that triggers activation of TP53 and the expression of TP53 target genes
1. If there’s a lot of BAX protein, it will start to insert into the membrane
2. Ultimately, it results in a situation where you’re forming new pores that cannot be blocked by the BCL-2 family members
3. This causes the release of Cytochrome C and death
43
How does phosphorylation activate apoptosis?
- BAD is able to bind to BCL-2, displacing it from the pore
- This allows the release of cytochrome C and causes cell death
44
What happens if the cell is enriched in an environment with growth factors?
- These growth factors acting as survival signals will activate a serine threonine kinase called AKT OR pKB
- This kinase phosphorylase’s BAD
- Phosphorylated BAD becomes sequestered in the cytoplasm and becomes no available to bind to bcl2
- Can’t displace it from the pore so cytochrome C is not released and the cell survives
