LECTURE 19 - AUTOPHAGY AND APOPTOSIS

what is autophagy

the mechanism in which the cell removes unneccessary or dysfunctional components

what are the stages involved in lysosome digestion of intracellular components

signal/activation

nucleation

expansion

fusion

degradation

explain autophagy signalling

signalling by mTOR (controlled by RAS-MAPK and PI3K AKT pathways)

mTOR switches off autophagy when cell is nutrient rich

when cell is scavenging mTOR will switch autophagy on

explain what happens in autophagosome nucleation

autophagosome is a double membraned structure with PtdIns-3-P in the outer membrane

PtdEtn is attached to LC3 I, forming LC3 II, which can associate with the membrane

explain degradation/macroautophagy

after autophagosome has fused with lysosome, contents are expelled within

hydrolases from the lysosome will break down the released contents

what is an autolysosome

the product of an autophagosome and lysosome fusing

explain microautophagy

involves the invagination of the lysosomal membrane

what is microautophagy used for

to control the size of or remove damaged organelles

what is apoptosis

programmed cell death

why is apoptosis highly regulated

because once it begins you cannot stop it

why is apoptosis needed in early organism development

to remove unwanted cells

e.g. tail, webs between fingers

what does too much apoptosis result in

neurodegeneration

what are the 2 ways apoptosis can occur

intrinsic pathway

extrinsic pathway

name some conditions increased apoptosis causes

myocardial infarction

stroke

neurodegenerative disease

name some conditions decreased apoptosis can cause

cacer

hyperplasia

graves disease

what are the 2 types of caspases

initiator caspases

executioner caspases

what does caspase stand for

cysteine dependent aspartate directed proteases

what do caspases do

proteolyse key cellular proteins

explain how the intrinsinc apoptosis pathway occurs

At the mitochondria:

• BH3 binds to Bc12

• Bc12 dissociates from Bax and Bak, so Bax and Bak oligomerise

• the oligomers form pores, making mitochondrial membrane permeable, allowing cytochrome C to enter the cytoplasm

• cytochrome C binds and activates Apaf 1

• procaspase 9 is recruited to the apoptosome and is activated within it, releasing caspase 9

• caspase 9 activates caspases 3,6,7

what is BC12

apoptosis inhibitor

what are Bax and Bak

pro-apoptopic proteins

what are the executioner caspases

3,6,7

what is the intrinsic initiator caspase

9

what is the extrinsic initiator caspase

8

explain the extrinsic apoptosis pathway

• activation of death recptor, like Fas, by binding of its ligand results in formation of death induced signalling complex (DISC)

• death domain of FADD binds to death domain of Fas

• death domain effector (DED) of FADD binds to DED of pro-caspase 8

• pro-caspase 8/10 is activated with DISC

• caspase 8/10 activates caspases 3,6,7

what does lipid flippase do

it flips phosphatidyl serine from inner leaflet to outer leaflet of plasma membrane

how is phopshatidylserine presented in apoptosis

it will start to be presented on the outer of the cell

how can we visualise apoptosis

bind protein to outer presenting phosphatidylserines and detect this

electrophorese cleaved genomic DNA

how does DNA exist in apoptosis

the DNA begins to cleave upon apoptosis