L17 - Apoptosis, necrosis and exitotoxicity

Question 1

define apoptosis

Answer 1

programmed cell death

Question 2

define necrosis

Answer 2

cell death from acute injury

Question 3

define excitotoxicity

Answer 3

type of cell death in neuronal tissue

Question 4

list some causes of necrosis

Answer 4

1. ischaemia
2. injury
3. hypoxia

Question 5

list some causes of apoptosis

Answer 5

1. withdrawal of GF
2. chemo
3. contact with cytotoxic T cells
4. development

Question 6

what are some characteristics of necrosis

Answer 6

1. membrane damage

2. leakage of cellular contents

Question 7

what does leakage of cellular contents in necrosis lead to?

Answer 7

inflammatory response

Question 8

what are some characteristics of apoptosis

Answer 8

1. intact membrane with blebbing
2. no leakage of cellular contents
3. condensed chromatin

Question 9

define blebbing

Answer 9

when the cytosol separates from the membrane leading to circular protrusions

Question 10

why is preventing cell leakage during apoptosis important?

Answer 10

1. avoid triggering inflammatory response

2. in neurons, release of exocytotic mediators eg glutamate from a cell can cause damage to nearby neurons

Question 11

describe process of apoptosis

Answer 11

1. chromatin condensation
2. blebbing
3. cell fragmentation forming apoptotic bodies
4. apoptotic bodies engulfed by phagocytes

Question 12

list some reasons why cells undergo apoptosis

Answer 12

1. metamorphosis (tadpole tail)
2. served developmental purpose (eg fetus hand development from bud - fingers)
3. cells infected by virus
4. cancer cells
5. cells with excessively damaged DNA

Question 13

what assay can detect apoptotic cells

Answer 13

TUNEL assay

1. run gel electrophoresis of cells induced apoptosis
2. overtime the ladder will increase as more fragments are forming
3. this generates more free ends of DNA
4. TUNEL assay uses fluorescence to detect these free ends

Question 14

what membrane lipid can act as a signalling molecule during apoptosis and how

Answer 14

phosphatidylserine

flips and concentrates on outer layer which signals to phagocytes

Question 15

what enzymes drive apoptosis

Answer 15

caspases (class of protease)

Question 16

characteristics of caspases

Answer 16

proteases that contain cysteine in active site

Question 17

caspases cleave their substrate at what site?

Answer 17

aspartate sites

Question 18

what is CAD

Answer 18

Caspase dependant DNAase

Question 19

what is the role of ICAD

Answer 19

binds to CAD enzymes inhibiting apoptosis

Question 20

how do caspases trigger apoptosis?

Answer 20

1. cleave ICAD-CAD rendering DNAase active
2. cleave lamins leading to nuclear envelope breakdown and fragmentation
3. cleave gelsolin causing blebbing

Question 21

what are the two apoptotic pathways

Answer 21

intrinsic (responding to intrinsic signals)

extrinsic (responding to extrinsic pathways)

Question 22

give examples of intrinsic signals

Answer 22

cytotoxic drugs

DNA damage

Question 23

describe the extrinsic apoptosis pathway

Answer 23

1. transmembrane death receptors (part of tumour necrosis factor - TNF- receptor family) respond to extrinsic signals by activating caspases

Question 24

describe thee intrinsic apoptosis pathway

Answer 24

1. stimuli cause leakage of mitochondrial membranes
2. cytochrome C leaks from M into cytoplasm
3. cytochrome C activates caspases

Question 25

what activates caspases

Answer 25

cytochrome C | transmembrane death receptors

Question 26

what amino acid can lead to excitotoxicity in nerve cells

Answer 26

glutamate

Question 27

what can cause glutamate release

Answer 27

hypoxia / hypoglycaemia

Question 28

explain the process of neuronal cell death by excitotoxicity

Answer 28

1. hypoxia/hypoglycaemia can cause glutamate leakage from broken vesicles 2. leads to prolonged activation of receptors (AMPA&NDMA) 3. AMPA causes NA+ influx which depolarises membrane 4. this dislodges Mg2+ from NMDA receptor leading to Ca2+ influx 5. Ca2+ dependant enzymes activated (lipases, DNAases)

Question 29

why does excitotoxicity only occur in nerve cells

Answer 29

only nerve cells express surface glutamate receptors

Question 30

what enzymes are activated during excitotoxicity

Answer 30

Ca2+ dependant ones (lipases, DNAases)

Question 31

what receptors does glutamate bind to in nerve cells

Answer 31

AMPA | NMDA

Question 32

what medical conditions can lead to severe apoptosis

Answer 32

heart attack | stroke

Question 33

name a disease caused by excessive apoptosis

Answer 33

diabetes type 1

Question 34

insufficient apoptosis can lead to what disease?

Answer 34

autoimmune diseases

Question 35

how are the effects of glutamate reduced (excitotoxicity)

Answer 35

glial cells take up glutamate from the synaptic cleft and convert it to glutamine

Question 36

in what diseases can excitotoxicity occur?

Answer 36

1. stroke 2. epilepsy 3. Parkinson's 4. Alzheimer's

Question 37

give an example of how apoptosis can be detected

Answer 37

by binding of labelled annexin V.

Question 38

what organisms never undergo apoptosis?

Answer 38

bacteria