Exam 4 Lesson 8 Flashcards
What extracellular factors integrate to influence cell growth?
nutrients
mitogens
Growth factors
survival factors
what is rapamycin? where does it come from?
a fungal antibiotic
from streptomycin
How does rapamycin limit cell growth?
a. mutagenize yeast
b. look for growth and rapamycin
c. identified mutants defective a protein kinase - “Target of Rapamycin” or TOR
What is TOR?
Target of rapamycin - a cytosolic protein kinase
What does TOR do?
It integrates growth factor signaling and nutrient status.
It leads to increased ribosome production and protein synthesis.
What is different in TOR expression between queen bees and hive bees? What happens if TOR is knocked out with RNAi in queen bees?
TOR protein is expressed at higher levels.
Knockout results in bees with size and morphology of worker bees.
How does myostatin regulate skeletal muscle cell size?
via the TOR pathway. An increase in TOR pathway results in increased muscle mass.
What does TOR pathway regulate?
a. longevity of unicellular and multicellular organisms
b. muscle mass
What does caloric reduction cause when it comes to TOR pathway? How?
increased life span
may be due to reduced incidence of cancer or other age-related diseases
What are the two types of cell death?
programmed cell death and necrosis
What are the two kinds of programmed cell death?
apoptosis and autophagic cell death
What happens during apoptosis?
a. cell shrinkage
b. “blebbing” of plasma membrane
c. orderly processing of DNA
d. degradation and cleavage of DNA
e. “clean” – no cellular leakage because membrane enclosed
f. no inflammatory response
What mediates autophagic cell death?
lysosomes
How is autophagic cell death similar to apoptosis?
similar hallmarks
neat - no inflammatory response
phagocytosis happens by adjacent cells
What is necrosis?
death of cell by insult/injury
causes cells to swell/burst with inflammatory response
Why do apoptosis (2)?
a. development – remove web b/w digits, for example
b. kill “dangerous” cells - infected or serious DNA damage
what are the key mediators of apoptosis?
caspases
What are caspases? What kinds are there? How many types?
special proteases that mediate apoptosis. There are ten types. There are effector and executioner caspases.
How does caspase work?
a. start with inactive pro-caspase that has inhibitor attached to it
b. signal results in auto cleavage of inhibitor
c. effector caspase is now active
d. effector caspase cleaves other caspases, leading to caspase cascade
e. caspase cascade turns into executioner caspases
f. executioner caspases target nuclear lamina, actin network, etc.
How do survival factors adjust the number of developing nerve cells to the amount of target tissues?
nerve cells receive an insufficient amount of survival factors to avoid apoptosis. More nerve cells are produced that can be used, but they are kept surviving with minimal survival factors until they can be eliminated.
How does DNA fragmentation work with executioner caspase?
a. start with endonuclease CAD associated with an inhibitor
b. executioner caspase cleaves inhibitor
c. CAD is active
d. CAD cuts chromosomal DNA between nucleosomes
In DNA fragmentation assay, why is there a barred pattern?
because nuclease is cleaving between histones
Two ways caspases are activated?
extrinsic pathway
intrinsic pathway
Describe extrinsic pathway.
extrinsic means from outside of cell.
a. Fas trimeric ligand (killer lymphocyte) on external cell binds with trimeric death receptor
b. receptors cluster and activate death domains on the receptor tails
c. death domains interact with similar domains on FADD adaptor protein
d. FADD protein recruits initiator caspase via a death effector domain on both FADD and caspase
e. this forms Death-inducing signaling complex (DISC)
f. within DISC, two initiator caspases interact and cleave one another to form an activated protease dimer
g. dimer cleaves itself in region linking protease to the death effector domain
h. this stabilizes and releases active caspase into cytosol, where it activates executioner caspases by cleaving them.
when is extrinsic pathway used?
a diseased cell targeted by immune cell
b. cell killed during development
What does intrinsic pathway require?
cytochrome C release from mitochondria
When is intrinsic pathway used?
for infected cell or DNA damage
Describe intrinsic pathway.
a. apoptotic intracellular stimulus gets mito to release cytochrome C
b. cyto C binds with Apaf1 and activates it
c. seven activated Apaf1 proteins form apoptosome
d. each Apaf1 protein has a caspase recruitment domain (CARD)
e. CARDs bind domains in similar caspase 9 molecules
f. once activated, caspase 9 cleaves and activates executioner caspases
g. this leads to caspase cascade that leads to apoptosis
What family of proteins regulates intrinsic pathway?
Bc12 family
How do Bc12 proteins control intrinsic pathway?
control release of Cytochrome C from mito
what kinds of Bc12 proteins are there?
pro-apoptotic and anti-apoptotic
pro-apoptotic Bc12 family members? How do they work?
Bax/Bak
form channels in outer mitochondrial membrane and help release cyto c into cytosol, which leads to a caspase cade
BH3 only protein
stimulated by pro-apoptotic proteins, it inhibits anti-apoptotic proteins
How does apoptotic stimulus work to activate effector Bc12 proteins on mitochondrial outer membrane?
Apoptotic stimulus aggregates active effector proteins and proteins release cyto C into cytosol.
How is intrinsic pathway activated?
a. start with inactive pathway, which consists of Bax/Bak proteins on mito membrane that are isolated from each other and blocked from cytosol by anti-apoptotic proteins.
b. activate BH3-only protein via apoptotic stimulus
c. BH3-only inhibits anti-apoptotic proteins
d. effector proteins aggregate and let cyto C out of mito
How does DNA damage lead to cell death?
DNA damage leads to activation of p53, a transcription factor. p53 leads to the expression of p21 and BH3-only.
P21 is a CKI that arrests cell cycle. BH3-only inhibits anti-apoptotic proteins that inhibit Bax/Bak.
Three ways that survival factors can inhibit apoptosis
a. increased production of anti-apoptotic Bc12 family protein
b. inactivation of pro-apoptotic BH3-only protein
c. inactivation of anti-IAPs
IAP
inhibitors of apoptosis
Hid
anti IAP protein in Drosophila
Bad
pro-apoptotic protein BH3-only
How do survival factors increase production of anti apoptotic BC12 protein family?
a. activate transcription regulator
b. regulator translocates into nucleus
c. Bc12 protein synthesis
How do survival factors inactivate pro-apoptotic BH3-only proteins?
a. activate Akt kinase
b. inactivate Bad
c. activate Bcl12 that is anti apoptotic
How does survival factor inactivate anti IAP in drosophile?
a. activate MAP kinase pathway
b. inactivates Hid, which works against the inhibition of apoptosis.
