ILA 13 Apoptosis

Question 1

What is apoptosis?

Answer 1

The death of cells which occurs as a normal and controlled part of an organism’s growth or development

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Question 2

Why is apoptosis important?

Answer 2

• Cellular Homeostasis - Immune response; water and salt balance; nerve activity; potassium levels; blood pH; tissue development, repair/organ integrity
• Protection - cells harboring dangerous mutations; viral/bacterial infection

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Question 3

The average adult loses how many cells per day via apoptosis?

Answer 3

50-70 billion

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Question 4

What are the 3 main modes of programmed cell death distinguished by their morphological changes?

Answer 4

1. Necrosis
2. Autophagic cell death
3. Apoptosis

Apoptosis was initially called “programmed cell death”

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Question 5

Describe what happens during necrosis.

Answer 5

• enlargement of cell volume
• swelling of organelles
• membrane bursting

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Question 6

Describe what happens during autophagic cell death.

Answer 6

• “cell death w/ autophagy”; autophagy does NOT induce death; inhibitors for autophagy do not inhibit cell death
• occurs when apoptosis is blocked
• massive vacuolization of cytoplasm which accumulate into autophagosomes

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Question 7

What are the morphological features of apoptosis?

Answer 7

• cell rounding
• reduction of cellular & nuclear volume
• Pyknosis - chromatin condensation
• Nuclear & DNA fragmentation
• Plasma blebbing
• apoptotic bodies
• engulfment by phagocytes

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Question 8

Explain what it seen in the picture.

What is responsible for this pattern?

Answer 8

DNA Laddering
Caspase activated- DNAse cuts DNA 200 base pairs
*only see this pattern on gel with apoptosis

caused by nuclear fragmentation of the apoptotic cell

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Question 9

What is blebbing?

Answer 9

• results when the cell’s cytoskeleton breaks up causing the membrane to bulge
• Bulges may break from the membrane forming apoptotic bodies. These bodies are taken up by phagocytes.

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Question 10

How does phosphatidylserine (PS) recognition work?

how does it cause apoptosis?

Answer 10

Normal Cells–> PS is on cytosolic side of plasma membrane

Apoptotic cells–> PS gets flipped to the extracellular side of the plasma membrane where it is recognized by receptors on phagocytes and engulfed

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Question 11

What is used to distinguish between the three types of PCD?

Answer 11

Morphological changes induced in each cell defines the pathway of death induced

Question directly from powerpoint

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Question 12

What are the key morphological changes brought on by apoptosis? (These are used for diagnosis)

Answer 12

Pyknosis, nuclear and DNA fragmentation, plasma blebbing

Question directly from the powerpoint

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Question 13

What are the 2 main pathways of apoptosis?

Answer 13

Intrinsic & Extrinsic

Main difference b/w 2 is Initiation. Execution & Phagocytosis are same

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Question 14

How does initiation occur in the intrinsic pathway?

also called mitochondrial pathway

Answer 14

initiated by signals from the cell’s own genes or detection of intracellular proteins that recognize DNA damage and involve the inhibition of anti- and activation of pro-apoptotic BCL2-proteins

includes genotoxic stress & growth factor removal

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Question 15

How does genotoxic stress induce apoptosis??

Answer 15

• Double stranded breaks activate PI3 kinases such as ATM and DNA-PKcs
• results in activation of p-53 which in turns activates the BCL-2 protein BAX

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Question 16

How does growth factor (GFs) removal induce apoptosis?

Answer 16

Removal of GFs which signal cell proliferation can cause apoptosis through activation of BAX

(ex. IL-2 stimulate T cell proliferation during immune response or Vascular Endothelial Growth Factor (VEGF) which promotes angiogenesis)

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Question 17

What is occurring in B cell lymphoma-2 (BCL-2)?

Answer 17

• translocation mutation carried by pts w/ follicular variant of b-cell lymphoma
• results in BCL2 overexpression
• BCL-2 does NOT promote cell proliferation; it inhibits apoptosis of cancerous B cells

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Question 18

What are the antiapoptotic regulators?

Answer 18

Bcl-2 and Bcl-xL

bind pro-apoptotic proteins (BAX/BAK) keeping them inactive

Question 19

What are the multidomain proapoptotic regulators?

Answer 19

• Bax and Bak
• These proteins are bound in their inactive form by BCL-2 in the cytoplasm

Question 20

What are the BH3-only proapoptotic regulators?

Answer 20

• Bid, Bad, Noxa, Puma, Bim
• These proteins bind BCL-2 releasing it from BAX/BAK

Question 21

Why is active BAX or BAK dangerous?

Answer 21

• Once in its active form, BAX or BAK migrates to the mitochondria where it forms a pore within the outer mitochondrial membrane
• This releases Cytochrome C stored in the intermembrane space –> APOPTOSIS

Question 22

What makes up the DISC (Death-inducing signal complex)?

Answer 22

FADD & Pro-caspase 8

Question 23

What are the two ligands for death receptors?

Answer 23

FasL and TNF-α

Question 24

Formation of the DISC causes what?

Answer 24

activation of pro-caspase 8 which in turn activates caspase 3 leading to Apoptosis