Apoptosis

Question 1

Necrotic cell death

Answer 1

Lysis of cell membrane leads to the release of cell’s content into extra cellular space

Occurs in trauma, bacterial/viral infection

More gradual

Question 2

Apoptosis

Answer 2

Initials of intracellular biochemical, which are not associated with cell lysis

Initiated by signals from damaged DNA, lack of necessary growth factors, forced entrance of the cell to S phase

Leads to the activation of proteases called capspases

Question 3

What are capspases?

Answer 3

Family of enzyme proteases

Hydrolyzes specific peptide bonds in proteins

Contribute to cells by inactive of important proteins

Tightly regulated

Question 4

Activation cascade of Caspase

Answer 4

Procaspase 8, 9, 10 –> auto catalytic just that they can work on themselves –> once bound to adaptor proteins and attached onto membrane, can be active Caspase –> Caspase 8, 9, 10 –> proteolytic activation of effector caspases 3, 6, 7 –> cellular proteins cleavage

activities are changing, not protein levels

Question 5

Characteristics of an apoptotic cell

Answer 5

Changes in plasma membrane protein content causes the membrane to become blabbed (fluidity) and to shed membranous particles that contain intracellular material

Endonucleases (Caspase activated DNase) are activate and they degrade chromosomal DNA into fragments

Degradation and changes in cytoskeletal proteins such as actin, plectin causes a dramatic change in cell shape

Question 6

What is the fate of an apoptotic cell?

Answer 6

The remains are up taken and digested by macrophages

Question 7

Death receptor pathway

Answer 7

Triggered by members of death receptor superfamily including CD95

Question 8

Death ligand

Answer 8

Proteins that activate the death receptor and downstream signaling

Ie; TNF and FAS ligand

Ligand binding to the receptor promotes binding of an intracellular adaptor protein to the cytoplasmic side of the receptor

Question 9

TNF, FAS ligand pathway

Answer 9

FADD- death domain adaptor protein

TNF (ligand) + Fas receptor + FADD protein –> procaspase 8, 9 ,10 –> Caspase cascade

TNF + FAS increases affinity to FADD

Question 10

Mitochondrial pathway of apoptosis- Cytochrome C, Caspase pathway (basics)

Answer 10

Mitochondria contains Cytochrome C in the mitochondrial membrane space

Translocation of cytochrome C to the cytosol via pores generated in the outer mitochondrial membrane, leads to apoptosis (Cytochrome C is essentials for cell survival)

Question 11

Cytochrome C, Caspase pathway- detailed outline

Answer 11

Outside mitochondria

Cytochrome C + Apaf1 + procaspase 9 –> apoptosome –> procaspase 9 activation to Caspase 9 –> released from complex to activate caspases 3, 6, 7

Activation not expression increased ***

Question 12

What regulates the release of Cytochrome C from the mitochondria?

Answer 12

A family of Bcl proteins (about 24 proteins)

Question 13

Anti-apoptotic Bcl proteins

Answer 13

Bcl-2 and Bcl-XL

Question 14

Pro-apoptotic Bcl proteins

Answer 14

Bax and Bak

Question 15

How does a pro-apoptotic Bcl family protein promote apoptosis?

Answer 15

The pores in the mitochondrial membrane through which Cytochrome C passes are generated by dimers or polymers of Bax and Bak

Bid, Bad, Noxa are pro-apoptotic facilitator proteins that help the formation of these stable dimers

Question 16

How does Bcl-2 prevent apoptosis?

Answer 16

Anti-apoptotic Bcl-2 and BclXL prevent cytochrome C leakage by binding to Bak and Bax and preventing their self association to form membrane proteins

Question 17

Ultimately what determines cell death or survival?

Answer 17

The ratio between anti and pro apoptotic proteins

Question 18

XIAP and Smac/Diablo

Answer 18

XIAP- Caspase inhibitor protein

X linked inhibitor of apoptosis

The protein Smac/Diablo inhibits XIAP and therefore allows activation of the Caspase cascade

Regulated mainly by proteins

Question 19

P53

Answer 19

P53 was first identified as a tumor suppressor protein

Transcription factor that regulates expression of various genes

Question 20

How does p53 induce apoptosis?

Answer 20

P53 increases the transcription of pro-apoptotic genes such as Bax and Noxa

Activates cytoplasmic Bax to bind to the mitochondrial membrane

Increases the expression of p21, which leads to cell cycle arrest

Question 21

How is MAPK activated?

Answer 21

The proteins MAPK: mitogenic activated protein kinases are activated by growth factor signals, UV light, radiation

Question 22

What does MAPK do?

Answer 22

MAPK known as Raf phosphorylates Bad, leading to its dissociation from the mitochondrial membrane –> leakage of cytochrome c –> leading to inhibition of apoptosis