Exam 2 - Apoptosis Flashcards
Apoptosis is the _____ for cells unless they are provided survival factors.
default
What are 4 instances when cells need to die?
- Infected with viruses
- Elimination of immune cells
- Tissue development
- DNA damage
T/F: Apoptosis is a part of animal development
True
What is an example of apoptosis being involved in an animal’s development?
Interdigital tissue being removed in orderly function
What type of molecule is MDM2?
E3 ubiquitin ligase
What does phosphate do to p53?
Frees it once bound
What phases does phosphorylation of p53 trigger to start in the cell cycle?
G2/M
What happens to cell division and apoptosis when there are mutations in Rb or Ras?
Increased cell division; normal apoptosis
= tumor
What happens to cell division and apoptosis when there is a mutation in p53?
Normal cell division; decreased apoptosis
= tumor
What is the cell shape/size in apoptosis vs. necrosis?
Apoptosis: single cells/small clusters; cell shrinkage/convolution
Necrosis: contiguous cells; cell swelling
What is the state of the nucleus in apoptosis vs. necrosis?
Apoptosis: pyknosis and karyorrhexis
Necrosis: Karyolysis, pyknosis, karyorrhexis
What is pyknosis?
Nucleus condensation
What is karyorrhexis?
Fragmentation of nucleus
What is karyolysis?
Chromatin dissolution
What is the state of the cell membrane in apoptosis vs. necrosis?
Apoptosis: intact cell membrane
Necrosis: Disrupted cell membrane
What is the state of the cytoplasm in apoptosis vs. necrosis?
Apoptosis: cytoplasm retained in apoptotic bodies
Necrosis: cytoplasm released
In which cell (apoptotic or necrotic) does inflammation occur?
Necrotic
What takes up vesicles released due to apoptosis?
Macrophages
What is a CAD?
Caspase activated DNA endonuclease
How is CAD activated?
- Inactive CAD bound to iCAD
- Executioner caspase cleaves iCAD
- CAD is active
What does CAD do when active and which assay can measure this?
Plays a role in DNA fragmentation by cleaving DNA everywhere that it is not protected by histones.
- TUNEL assay
How does the TUNEL assay work?
DNA-damaged site is labeled in the cell using a fluorescent assay.
What events does necrosis typically follow?
Injury, trauma, lack of blood, lack of nutrient supply
In what organism is apoptosis normally seen?
Animals
What changes orientation in the cell membrane during apoptosis and why is this important?
Phospholipid phosphatidyl serine; presents an “eat-me” signal to macrophages so they can be phagocytosed
Where is the active site on a caspase?
Cysteine
Where do caspases cleave?
Aspartic acid
What are the 2 classes of caspases?
- Initiator caspases
2. Executioner caspases
What is the signal flow of an initiator caspase/how is it activated?
Inactive monomers dimerize upon receiving an apoptotic signal on adaptor proteins (binds to pts)
How is the executioner caspase activated?
It is cleaved by the active initiator caspase
What does an active initiator caspase do?
Activates executioner caspase by cleaving it
What does an active executioner caspase do?
Cleaves multiple substrates leading to apoptosis
T/F: Once a caspase activates another to begin a cascade, the cell can sometimes escape that cascade to avoid apoptosis.
False; once the cell is in the cascade, there is no turning back – it is destined to apoptose.
What protein is cleaved by caspase to allow the cell to collapse and shrink?
actin
What proteins are cleaved by caspase that breaks down the nucleus and what is the result?
Lamins; result in the cell’s DNA being exposed, allowing endonucleases to come in and break down the DNA.
What are the 2 mechanisms by which initiator caspase activates?
- Extrinsic pathway
2. Intrinsic pathway
What is the extrinsic pathway?
Death receptor pathway; always involves 2 cells (ligand–receptor)
What is the intrinsic pathway?
Mitochondrial pathway
What activates the intrinsic pathway?
Intracellular factors (oxidative stress, hypoxia, nutrient deprivation)
What does the intrinsic pathway cause?
Mitochondrial outer membrane permeabilization and cytochrome C leakage into the cytoplasm from mitochondria
Where is cytochrome C present in mitochondria?
Intermembrane space
How many subunits does the human apoptosome have?
7
What activates the human apoptosome?
cytochrome C
How many subunits does the fruit fly apoptosome have?
8
What activates the fruit fly apoptosome?
Cytochrome C BUT may not always need it for activation
Where do caspases bind on the nematode apoptosome?
Back side of the ring
What does cytochrome C fuse with when it leaves the cell?
Green Fluorescent Protein
Bax is a type of _____ protein.
Bcl2
How does Bax assist in cytochrome C leakage?
Bax proteins are present in the mitochondrial membrane; they aggregate under an apoptotic stimulus and provide pores for cytochrome C and other pts to exit the cell
What are the 3 types of Bcl2 proteins that regulate the intrisic pathway?
- Pro-apoptotic (pore-forming) Bax
- Anti-apoptotic Bcl2
- Proapoptotic BH3-only Bad
What happens if Bcl-2 binds Bax?
No cytochrome C leakage bc no pores can be formed
What happens when Bad binds Bax?
Bax aggregation and cytochrome C leakage (formation of pores)
What does IGF-1 stimulate?
Cell survival and growth
What does IGF-1 inhibit?
Apoptosis
What type of signaling pathway does IGF-1 utilize?
enzyme-linked
What are the 7 steps of the IGF-1 pathway to inhibit apoptosis?
- IGF-1 (survival signal) binds receptor tyrosine kinase
- RTK is phosphorylated and activated
- PIP₂ –> PIP₃
- Akt is phosphorylated and activated
- Akt phosphorylates Bad (bound to Bcl-2)
- Bad dissociates from Bcl-2
- Bcl-2 is activated and inhibits apoptosis
Other than going into the nucleus, what other way does p53 induce apoptosis?
By dissociating from mdm2 and stimulating aggregation of Bax and Bak proteins, which form pores in mitochondria for cytochrome C leakage.
p53 is mutated in over ___% of cancers.
50%
What are the 2 main ways that apoptosis can be inhibited through survival factors?
- Receptor regulates transcription in the nucleus, resulting in Bcl-2 proteins being present
- Active Akt kinase causes dissociation of Bcl-2 and Bad – Bad is inactivated, Bcl-2 is active and inhibits apoptosis
What is a DISC?
Death-Inducing Signaling Complex
How does the death receptor (extrinsic) pathway function (5 steps)?
- Killer lymphocyte with Fas ligand binds to Fas death receptor on cell surface
- DISC is assembled
- Caspase-8 is cleaved and activated
- Executioner caspases are activated
- Target cell udergoes apoptosis
How is apoptosis activated from inside the cell (intrinsic pathway) (4 steps)?
- Cytochrome C released and binds to Apaf-1
- Apaf-1 aggegates and binds to procaspase-9
- Procaspase-9 is activated
- Caspase cascade is activated
Cells are constantly _____ multiple inputs to decide whether to divide, differentiate, or die.
balancing
What 3 processes can cells go through during proper organ development?
- Proliferation
- Survival
- Apoptosis
Proper organ development requires _____.
Coordination of cellular processes
What is microphthalmia?
“Small eye” phenotype; proliferation defect; genetic/infectious/environmental
Microphthalmia is a _____ defect.
proliferation
What occurs when there is too much proliferation of muscle cells?
Hypertrophy; myostatin mutation
What is the normal role of myostatin?
Differentiation factor that inhibits myogenesis.
What are 4 examples of mutations in myostatin?
- Mighty mice
- Belgian Blue Cattle
- Texel sheep
- Whippets
What occurs in a myostatin mutation at the genetic level?
Sequence is truncated (313 AAs instead of normal 375 AA protein)
- TGT –> TGA
- Cysteine –> stop codon
What is syndactyly?
Fusion of digits
How does syndactyly occur?
Incomplete apoptosis of interdigital cells between developing digits
Where is survival best understood?
developing brain
What do cells compete for in survival?
Survival factors
What 2 things are required by cells for normal development?
- Proliferation
2. Apoptosis
