Lecture 22: Apoptosis-programmed cell death Flashcards Preview

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Flashcards in Lecture 22: Apoptosis-programmed cell death Deck (43):
1

Programmed Cell Death

• Programmed cell death is a vital process to the overall good of a multicellular organism 

• Apoptosis is one form of programmed cell death 

• Up to half of the neurons in a developing vertebrate organism die soon after they are formed (target selection) 

• Some tissues are formed and most are maintained at a consistent size by selective apoptosis 

2

Morphological changes during apoptosis 

• Cells shrink in size 

• Chromatin condenses and fragments 

• The cytoskeleton disassembles 

• The nuclear envelope collapses 

• The cell surface distends or “blebs” 

• The plasma membrane is chemically altered to promote phagocytosis

3

____ results from acute injury and the cells typically swell and burst causing an inflammatory response. 

Cell necrosis

4

_____ are essentially degraded from the inside out without damage to neighboring cells 

Apoptotic cells

5

Cell death is induced by the absence or low amounts of “_______” 

survival factors

6

Biochemical changes associated with apoptosis 

• DNA fragmentation 

• Loss of phospholipid asymmetry in the plasma membrane.

    – Phosphatidylserine flips to the outer leaflet 

• Cell surface modifications that promote phagocytosis 

• Loss of Proton Motive force in mitochondria 

• Some of these changes can be detected in dying cells 

7

_____ that are activated as a result of apoptosis cut genomic DNA into a characteristic ladder patterns due to cleavage in the linker regions between nucleosomes 

Endonucleases

8

How does the TUNEL assay detect apoptosis?

The newly generated DNA ends that result from genomic cleavage can be detected in cells by modifying the ends of DNA with a fluorescent nucleotide. 

 

TUNEL=TdT mediated dUTP nick end labeling 

TdT=terminal deoxynucleotide transferase

9

____ is responsible for the apoptosis that is involved in limb formation

BMP

10

The primary mechanism of destruction is the activation of proteases called ____ (active site cys, cleave at specific asp residues) 

caspases

11

Not all caspases are involved in apoptosis, some are important for the _____

inflammatory response 

12

An activation cascade is thought to be set in motion by _____ that are activated in response to a signal through their _____. 

initiator caspases

caspase recruitment domain (CARD)

13

Once activated, these initiator caspases propagate the cascade of activation through ______

executioner caspases

14

Caspases involved in inflamation

– Caspase 1 (Interleukin-1 converting enzyme, ICE), 2, 4 

15

Initiator caspases

– Extrinsic pathway 

• Caspases 8, 10 

– Intrinsic pathway 

• Caspases 2, 9 

16

Executioner Caspases

– Caspases 3, 6, and 7 

17

Activation of Caspases

A image thumb
18

Caspase Cascade

A image thumb
19

How do caspases trigger DNA fragmentation

-executioner caspases cleave iCAD, cleave iCAD releases CAD which cuts DNA between nucleosomes

20

Extrinsic pathway 

– Activation of Cell surface receptors (death receptors) 

21

Intrinsic pathway 

– Triggered in response to injury or stress 

– DNA damage 

– Lack of oxygen, nutrients, or survival signals 

22

Extrinsic pathway of Apoptosis

• Cell surface receptors (death receptors) activate the extrinsic pathway 

• Single span membrane proteins with an extracellular ligand binding domain and an intracellular death domain 

• Receptors are homotrimers of the tumor necrosis factor (TNF) family 

• Includes the TNF receptors itself and the Fas death receptor

23

Induction of apoptosis by extracellular stimuli 

Extrinsic pathway by activation of Fas death receptors 

A image thumb
24

Intrinsic Pathway of Apoptosis

• Depends on the release of mitochondrial intermembrane space proteins into the cytosol 

• The release of cytochrome c, the electron carrier between ETS complex III and cytochrome oxidase, can trigger apoptosis 

• Released cytochrome c binds to a procaspase activating adapter called Apaf-1 (apoptotic protease activating factor), driving its oligomerization into a wheel like heptamer called the apoptosome 

• The aggregated Apaf-1 binds and activates caspase-9 by induced proximity 

• This initiator caspase-9 activates downstream executioner caspases

25

Induction of apoptosis by intracellular stimuli 

A image thumb
26

_____ proteins control the release of cytochrome c from mitochondria 

Bcl-2 (B-cell lymphoma-2)

27

_____ inhibit apoptosis (anti-apoptotic) 

 (Bcl-2 and BclXL)

28

Other family members _____ promote apoptosis (pro-apoptotic)by increasing cytochrome c release from mitochondria. 

(Bax and Bac)

29

anti-apoptotic Bcl2 family proteins have:

all 4 BH domains

30

pro-apoptotic Bcl2 family proteins have

BH 1-3 domains

31

BH3 only pro-apoptotic proteins include: 

Bad, Bim, Bid, Puma, Noxa

32

___ is tightly bound to the mitochondrial membrane even in the absence of an apoptotic signal 

Bak

33

___ is mainly located in the cytosol an translocates to the mitochondria in response to an apoptotic signal 

Bax

34

Upon activation, Bax and Bak generate....

pore-forming proteins in the mitochondrial outer membrane 

35

Bcl2 mechanism of cytochrome C release

A image thumb
36

Bcl-2 and Bcl-XL

• Located on the cytosolic surface of the mitochondrial outer membrane 

• Binds to bax to prevent bax oligomerization

37

BH3 only proteins 

  • proapoptotic
  • Binds to Bcl2 to inhibit their ability to bind and inhibit Bak or Bax

38

____ is transcriptionally upregulated in the absence of cell survival signals 

Bim

39

___ and ___ are transcriptionally upregulated in response to DNA damage

Puma and Noxa

40

Bid is cleaved to tBid by activated ___ coordinating the extrinsic and intrinisic pathways in some cells 

caspase 8

41

Inhibitors of Apoptosis (IAPs) 

• Caspase inhibitors 

• Used by viruses to prevent the host cell form committing suicide prior to viral replication 

• IAPs can be countered by anti-IAPs in some cells 

• Anti-IAPs bind to IAP and prevent them from inhibiting caspase 

• Genetic manipulation of IAP or anti-IAPs have dire consequneces in flies indicating the delicate balance needed for apoptosis during development 

42

Three methods of survival factor inhibition of apoptosis 

  1. increased production of anti-apoptotic Bcl2 family protein
  2. inactivation of pro-apoptotic BH3-only protein
  3. inactivation of anti-IAPs

43

Apoptotic cells are cleared by ____

phagocytosis