Apoptosis. Flashcards
Define caspase enzymes?
Enzymes that are involved in apoptosis.
What is apoptosis?
It is defined as programmed cell death.
Apoptosis is an important cellular function in what kind of organisms?
In multi-cellular organisms that must undergo growth and death.
What are the 2 different ways in which a cell can undergo cell death?
Necrosis.
Apoptosis.
When will a cell die by necrosis?
When the cell is exposed to a harmful environment.
When the tissue that contains the cell suffers an injury which damages the cell.
What are the 3 steps of necrosis?
The swelling of the nucleus and other cellular tissues.
This swelling eventually causes the cell to burst and the cellular contents will be expelled.
The release of the cellular contents activates antigens and this leads to an immune response and inflammation.
What are the 3 steps of apoptosis?
By condensation of the chromosomes and cell shrinkage.
The cellular organelles and cell membranes are preserved.
The cell is engulfed or phagocytosed by macrophages.
What is necrosis characterised by?
Inflammation.
What is apoptosis characterised by?
Caspase’s and DNA fragmentation.
What does apoptosis enable the body to do?
To get rid of unwanted or defective cells via a process which does not activate the inflammatory response.
What happens when the cell receives the signal telling it that apoptosis needs to take place?
It induces the shrinkage of chromatin within the nucleus and this causes the cytoplasm to shrink as well.
What is the membranous shrinkage that is characteristic of apoptosis known as?
As blebbing.
How long will blebbing continue for?
Until apoptotic bodies form.
What happens in apoptosis once the apoptotic bodies have formed?
Once the apoptotic bodies have formed macrophages will phagocytose them.
What is one of the major molecular markers of apoptosis?
Phosphatidylserine.
Where is phosphatidylserine found on a cell that is marked for apoptosis?
It is found on the surface of the outer membrane of the phospholipid bilayer.
What is the phosphatidylserine molecule also known as?
As the eat me signal as it acts as a signal for macrophages to ingest the cell.
Where is phosphatidylserine found on cells that are not marked for apoptosis?
On the inner membrane of the phospholipid bilayer.
How does phosphatidylserine move from the inner membrane to the outer membrane in a cell that is marked for apoptosis?
Caspase proteins 3 and 7 activate an enzyme called XRP-8 which will catalyse lipid scrambling.
This re-arrange’s the phospholipids and place’s phosphatidylserine on the outer membrane.
Does the process of apoptosis lead to an inflammatory response?
No
What is the first step of DNA degradation within cells marked for apoptosis?
Caspase proteins will activate a set of endonuclease enzymes called caspase activated DNAase.
What is the second step of DNA degradation within cells marked for apoptosis, after the caspase activated DNAAase has been activated?
They will cleave the chromosomes in the linker region that lies between the nucleosomes.
How can the cleavage of DNA by the caspase activated DNAAase enzymes be visualised?
By gel electrophoresis as fragments will separate into different bands on the gel.
How would DNA that had undergone necrosis appear after electrophoresis?
There would only be small remnants visible at the bottom the gel.
When will apoptosis be heavily used during development?
When forming the fingers and toes in the foetus.
Why is apoptosis heavily used during the formation of fingers and toes of the foetus?
Because the hands and feet of humans are webbed during the early embryonic stages.
How are the cells that make up the webbing within fingers and toes during foetal development removed?
By apoptosis.
Why is apoptosis important in frog development?
It is responsible for the removal of the tadpole tail.
What molecule stimulates the removal of a tadpole tail?
A particular thyroid hormone.
What 4 ways is apoptosis essential during adulthood?
It allows for cells that have DNA damage to be destroyed.
It destroys cells that have been infected by viruses and this helps to stop viral infections from spreading.
It helps to eliminate cancer cells.
It will eliminate any auto-immune components of the immune system.
How long does the c.elegans take to develop?
It takes exactly 3 days to develop an egg to a sexually mature organism.
How many cells are present in the adult c.elegans?
Exactly 959 somatic cells all of which have a lineage and function that has been determined.
What process allowed for determining the function of cells within a c.elegans?
Laser ablation.
How many cells will the 959 cells that form the C.elegans arise from?
From 1090 original cells.
How do the 1090 original cells of the c.elegans become the 959 cells that form the developed adult?
131 are killed by apoptosis.
What type of cells make up the 302 cells that are killed by apoptosis in the developing c.elegans?
Neurons.
Who was the scientist that discovered what controlled the fate of the 131 cells that are killed by apoptosis in a developing C.elegans?
Horvitz.
How did Horvitz discover what controlled the fate of the 131 cells that are killed by apoptosis in a developing C.elegans?
He screened for worms that contained undead cells.
What did Horvitz find in the undead cells of c.elegans?
He discovered that they contained 3 interesting genes called CED-3, CED-4 and CED-9.
What did Horvitz find happened to developing c.elegans that expressed mutations in the CED-3 and CED-4 genes?
They not undergo any apoptosis at all and all 1090 cells survived.
What did Horvitz find happened to developing c.elegans that expressed mutations in the CED-9 gene?
They did suffer from apoptosis and this apoptosis killed all 1090 cells.
What did Horzitz conclude from his study of developing C.elegans?
That the genes CED-3 and CED-4 were required for apoptosis.
That CED-9 was responsible for suppressing apoptosis.
Do mammals contain CED genes?
No, but they do contain homologues which are known as caspase enzymes.
What does the name caspase stand for?
For Cysteine dependent ASpartate directed ProteASE’s.
What are caspase enzymes?
A family of cysteine protease’s which play essential roles in apoptosis.
How does a caspase function?
It uses the cysteine in its active site to cleave aspartic acid peptide bonds within proteins.
What kind of enzyme is a capsase?
A cysteine aspartase.
When are caspase enzymes regulated?
At the post transcriptional level.
Why are caspases regulated at the post transcriptional level?
As they are first synthesised as inactive pro-caspase’s.
What structures make up an inactive pro-caspase?
A prodomain and a small and large subunit.
What molecules will activate pro-caspase’s?
Via proteolytic cleavage by another member of the caspase family.
How are pro-caspase’s activated?
By the proteolytic cleavage of the pro-domain.
What structures make up an active pro-caspase?
The small and large subunits.
What doe the initial activation of a procaspase enzyme amplify?
It leads to a chain reaction which activate more pro-caspase enzymes.
What are the functions of the CED genes in C.elegans?
Depending on the CED gene, their function is to activate and inhibit apoptosis within the organism.
Do humans contain CED genes?
No, they contain analogues of these genes called BCL genes.
What happens within a cell when the signal for apoptosis arrives in c.elegans?
It will directly inhibit the CED-9 gene.
What happens within a cell when the signal for apoptosis arrives in humans?
It will directly inhibit the BCL-2 gene.
The BCL-2 and CED-9 genes can be described as being what kind of genes?
As anti apoptosis genes.
What happens once the CED-9 gene has been inhibited in C.elegans?
The CED-3 and CED-4 genes will be activated and these genes will promote apoptosis within the cell.
What is the function of the EGL-1 gene in c.elegans?
It will activate apoptosis by activating CED-3 and CED-4.
What happens in humans when the BCL-2 gene is inbhibited by the death signal?
It will activate the APAF-1 gene and a caspase enzyme and this will lead to apoptosis.
How can c.elegans or human cells stop apoptosis after the death signal has affected a cell?
By the production of survival factors.
What are survival factors?
Trophic factors that can inhibit CED-4 and APAF-1.
What genes can inhibit the BCL-2 gene?
By the activation of the EGL-1 gene or the BAD gene and this will also lead to apoptosis.
Can any extrinsic sources activate apoptosis?
Yes. E.g. A viral or bacterial infection.
Why will infections activate apoptosis?
They will activate T lymphocytes which will induce apoptosis in cells that have been infected.
What is the first step of T lymphocyte induced apoptosis?
T lymphocytes use their FAS ligand, to bind to a cells FAS death receptor and this activates and FADD protein.
What is the second step of T lymphocyte induced apoptosis, after the FADD protein has been activated?
The 2 subunits of the FADD proteins bind to caspase 8 or 10.
What is an FADD protein?
The FAS associated death domain (FADD protein).
What are the 2 subunits of the FADD protein?
The death domain and the death effector domain.
What is the third step of T lymphocyte induced apoptosis, after the FADD protein has bound to caspase 8 or 10?
It activates the caspase enzyme.
What is the fourth step of T lymphocyte induced apoptosis, after caspase 8 or 10 has been activated?
The complex of proteins moves to the cell membrane and binds to the intracellular domain of the FAS death receptor.
What is formed during T lymphocyte induced apoptosis after the complex of proteins has bound to the intracellular domain of the FAS death receptor?
The death induced signalling complex (DISC).
What is the fith step of T lymphocyte induced apoptosis, after caspase 8 or 10 has been activated?
The large subunits of the caspase proteins will detach, leaving the small subunits attached to the DISC.
This leads to the activation of more caspase enzymes and eventually the cell will be destroyed.
What usually causes the intrinsic signals that lead to apoptosis?
Damaged or stressed cells.
How can damaged or stressed cells induce apoptosis?
By releasing cytochrome-C from the mitochondria.
What is the first step of self induced apoptosis after cytochrome-C has been released from the mitochondria?
The released cytochrome C molecules bind to APAF-1 proteins by displacing a CARD domain.
What is a card domain?
Caspase activation and recruitment domain.
Where is the CARD domain displaced to when cytochrome C binds to the APAF-1 protein?
It is displaced to the end of the APAF-1 protein.
What is the second step of self induced apoptosis after cytochrome-C has bound to the APAF-1 protein?
Several similar APAF-1’s use their CARD molecules to bind and create a molecule called the apoptosome.
What is the apoptosome formed from?
From several APAF-1/cytochrome C complexes, all of which are bound together by their CARD domains.
What is the third step of self induced apoptosis after the apoptosome has been formed?
The active apoptosome recruits and binds to the CARD domain on procaspase 9.
What is the fourth step of self induced apoptosis after the apoptosome has bound to procaspase 9?
The caspase proteins and this starts a chain reaction that activates more caspase’s and leads to apoptosis.
What are the BCL-2 protein family?
A group of proteins which control the critical step in a cells commitment to apoptosis.
What is the job of the BCL-2 and BCL-X proteins?
They are anti-apoptotic proteins determine the permeability of the outer mitochondrial membrane.
What is the job of the BCL-2/BH213 proteins such as BAX and BAK?
They are pro-apoptotoic proteins that allow the outer mitochondrial membrane to become permeable and secrete cytochrome C.
What is the job of the BCL-2/BH3 proteins such as BAD, BIM, BID, PUMA and NOXA?
They will activate the BH123 proteins that are pro-apoptotic.
What are mitogens?
Extracellular factors that mimic growth factors by stimulating cell division.
What is the first step by which mitogens stimulate cell division?
The mitogens bind to specific receptors on the cell membrane and activate the RAS protein.
What is the scond step by which mitogens stimulate cell division, after the RAS protein has been activated?
The RAS protein stimulates the activation of MAP kinase.
What is the second step by which mitogens stimulate cell division, after the MAP kinase has been activated?
MAP kinase leads to the activation of the MYC gene and this will lead to the production of MYC proteins.
What is the third step by which mitogens stimulate cell division, after the MYC proteins have been produced?
The MIC proteins tells the cell to begin to divide by activating a G1-CDK complex and an SCF complex.
What is the SCF-complex that is activated during mitogen stimulated cell division?
It is a ubiquitin ligase.
What is the fourth step by which mitogens stimulate cell division, after the G1-CDK and SCF complexes have been activated?
The SCF complex will lead to the poly-ubiquitination and destruction of the CKI protein.
What happens if mitogen production is uncontrolled?
It can lead to uncontrolled cell division.
How can the body repsond to excessive mitogen production?
By activating P-19-ARF.
How does P-19-ARF lead to apoptosis?
It binds to and inhibits MDM-2 and this prevents the degradation of P-53.
This activates the P-53 pathway which will direct the cell towards apoptosis.
What are survival factors?
Extracellular signals that can control the fate of cells as their signals will inhibit apoptosis.
How are nerve cells produced during development?
They are produced in excess.
What happens to the excess nerve cells that are produced during development?
They all compete with each other for limited amounts of survival factors which are secreted by target cells.
What determines which nerve cells survive during development?
The nerve cells that receive enough survival factors will survive and those that don’t receive enough will die.
What are common survival factors that are secreted by cells during development?
Neurotropins.
The binding of survival factors to cell surface receptors leads to the activation of what?
Protein kinase B.
What is the job of protein kinase B after it has been activated by survival factors?
It phosphorylates and inactivates the BAD protein.
This prevents BAD from binding to the apoptosis inhibitor BCL-2 and this keeps BCL-2 active and prevents apoptosis from occurring.
Will protein kinase B only bind to BCL-2 to prevent apoptosis?
No, it can also bind to and inactivate other proteins which promote apoptosis such as FORKHEAD.
