Tissue Cell and Renewal Flashcards
What is apoptosis? How does it occur?
Apoptosis- programmed cell death; this process is part of controlling a cell’s growth and development.
In apoptosis, the organelles within parenchymal cells separate, condense and fragment into pieces. Then phagocytotic cells engulf fragmented cell and send to lysosomes where they are degraded.
What is a residual body?
Residual body- vesicle filled with particles that cannot be digested.
Describe the different morphological characteristics of apoptotic cell death.
Characteristics:
- apoptosing cells shrink, condense and round up.
- Nuclear envelope disassembles
- Chromatin condenses (pyknosis) and breaks into fragments (karyorrhexis)
- Cytoskeleton collapses
- PM blebs and bulges, but PM still remains intact
- Cell corpse may break into fragments (called apoptotic bodies)
- Surface of corpse changes to be recognized by neighboring cells for phagocytosis
- engulfed by neighboring cells before contents spill out (apoptosis vanish)
Compare and contrast a normal WBC vs. apoptotic WBC.
Normal- wbc has microvilli, membrane covered microgilaments and extensions of cytoskeleton, round.
Apoptotic- wbc has blebs (regions detached from cytoskeleton that has broken down).
Differentiate between apoptosis and necrosis functionally and physically.
Apoptosis- active, ATP-dependent process, mutations that can prevent apoptosis. Also cell breakdown is clean, membrane still bound.
Necrosis- passive process, no mutation can prevent necrosis from occurring. Cell break down is messy, contents LEAK out.
Compare and contrast Apoptosis and Necrosis
Apoptosis- single cells or small cluster of cells, cell shrinkage and convolution, chromatin condensation (pyknosis) and fragmentation (karyorrhexis); cell membrane is intact, cytoplasm is retained in apoptotic bodies, ATP-dependent, genetically programmed, little or no inflammation.
Necrosis- contiguous cells (adjacent), cell swelling, cell separation (karyolysis, pyknosis, karyorrhexis), disrupted cell membrane, cytoplasm released, ATP INDEPENDENT, NOT genetically programmed, may cause inflammation.
What two major pathways cause apoptosis? Differentiate between the two pathways.
The intrinsic and extrinsic pathway both cause apoptosis.
Intrinsic pathway- cell ITSELF will decide if it should die (something will happen to cell that will make it undergo apoptosis).
Extrinsic pathway- once cell will tell ANOTHER cell that it needs to die.
Describe what occurs in the intrinsic pathway.
In intrinsic pathway you have death stimulus like radiation, hypoxia. In this pathway, the initiator caspase must be cleaved to become activated. Death receptor will initiate cascade of caspase.
Bc12 family of proteins are involved- BH3 only proteins, Bc12 protein and bak and bax.
In pathway, cytochrome c is present, with Killer T cells that damage cell and induce cell death.
What must occur in the extrinsic pathway of apoptosis?
In extrinsic pathway, the death ligand must bind to death receptor to initiate the apoptosis.
What feature of apoptosis is common to both extrinsic and intrinsic pathways? What is the amplification step in this cascade?
The CASPASE CASCADE is common to both pathways. A caspase must be cleaved to be activated.
The amplification step is during the executioner caspase step, leading to cleavage of nuclear components.
Starting from procaspase, how is one caspase molecule activated?
initially you have two inactive procaspase molecules. These procaspase molecules will then be cleaved at their sites (cleave pro domains) and assemble together to form one active caspase molecule.
Explain the reason behind the name CASPASES. What does this name signify?
Caspases- C is for cysteine and ASP is for ASPartate.
Caspases are proteinases that have a cysteine at their active site and cleave their target proteins at specific ASPARTIC Residues.
What happens when during proteolytic cleavage of pro-caspase?
cleavage of pro-caspase will rearrange the protein to form active site (important to activate enzymes).
Compare and contrast inititator caspases and executioner caspases. What do they have in common? how do they differ?
Initiator caspases and executioner caspases have different structures.
Both initiator and executioner caspases are activated by proteolytic cleavage.
Initiator caspases are activated when they DIMERIZE
Executioner caspases are activated when they are CLEAVED by INITITATOR caspases.
What occurs in the amplification step of proteolytic cascade?
In the amplification step:
one initiator caspase can activate many executioner caspases, leading to amplification of apoptotic signal.
a proteolytic cascade involving initiator and executioner caspase lead to apoptosis.
Describe the different functions of proteins in Bc12 family of proteins? Which are the pro-apoptosis? Which are anti-apoptosis?
Bc12 family of proteins:
1. proteins that are pro-apoptosis- BH3 only proteins, and Bak and Bax proteins.
2. Proteins that are anti-apoptosis- Bc12- tries to keep the cell alive.
BH3 only proteins- sense difference signals and act as sensors to inhibit anti-apoptotic cells by inactivating Bc12. BH3 activates Bak and Bax proteins.
Bc12- try and keep cell alive and induce, by inhibiting Bak and Bax proteins.
The Bak and Bax proteins- pro-apoptosis; they make holes in mitochondria to release cytochrome c
Once cytochrome c is lost, cell is not functional
Cytochrome c will bind to protein Apaf1 (adaptor) and form complex apoptosome which activates initiator caspase.
What role does BH3-only proteins play in apoptosis?
BH3 only proteins- acts as sensors of a variety of apoptotic signals. They inhibit anti-apoptotic Bc12 proteins, and allow pro-apoptotic effector proteins to cluster and release cytochrome C.
Some BH3 only proteins- bind effector proteins directly to stimulate aggregation.
What is the role of anti-apoptotic Bc12 protein and BclXL? Where are they located?
They are located on cytosolic surface of outer mitochondrial membrane, where they bind and block activation (by preventing oligomerization) of pro-apoptotic (Bax and and Bak ) Bc12 family proteins.
Why are Bc12 proteins important?
Every cell needs at least one ACTIVE anti-apoptotic Bc12 protein to SURVIVE.
How do all proteins in Bc12 family proteins regulate apoptosis?
they regulate apoptosis by controlling the mitochondrial membrane permeability and release of cytochrome c and other intermembrane proteins into the cytosol.
What is the role of Bc12 family effector proteins (Bak and Bax)?
What would happen to cell without effector Bc12 proteins?
The activated pro-apoptotic effector Bc12 proteins (Bak and Bax) AGGREGATE on outer mitochondrial membrane and cause intermembrane proteins to be released.
Without effector Bc12 proteins, a cell cannot respond to an intrinsic apoptotic signal.
Describe the involvement of mitochondria in the intrinsic pathway of apoptosis.
The intrinsic pathway of apoptosis involves mitochondria, as the release of cytochrome c from intermembrane space of mitochondria goes into cytosol.
Describe the steps that occur in intrinsic pathway of apoptosis.
Steps in intrinsic pathway:
- Diverse apoptotic stimuli (not death receptor) initiates signaling that activates Bc12 family proteins Bak and Bax.
- Bak and Bax activation changes inner mitochondrial membrane and leads to opening of a pore.
- the loss of mitochondrial transmembrane potential occurs and causes release of mitochondrial proteins into cytosol.
- Cytochrome C binds adaptor protein (Apaf1), which heptamerizes into apoptosome.
- after binding to cyto c, adaptor protein binds pro-caspase-9 (initiator caspase) and forms hexamer.
- multimerization of pro-caspase-9 leads to proteolytic cleavage and activation. It can now cleave executioner caspases.
How can apoptotic cells with released mitochondrial cyto c be differentiated from non apoptotic cells (retain cytochrome)
They can be differentiated through FLOURESCENCE MICROSCOPY.
a cell that merged green fluorescence in cell indicates cell with cytochrome c in cytosol, left mitochondria.
What happens when cytochrome C binds to adaptor protein (Apaf1)?
The binding of cytochrome C causes the adaptor protein to unfold partly, exposing a domain that interacts with same domain in other activated adaptor protein molecules.
What is an apoptosome?
A protein complex made of adaptor proteins, cytochrome C and Pro-caspase-9 molecules bound together into a hexamer shape.
What does the adaptor protein do, after binding to cytochrome C?
After binding cytochrome C, adaptor protein binds to pro-capspase-9 (initiator caspase) molecules to form hexamer.
Describe the steps that occur in the extrinsic pathway, and the cellular structures involved.
Extrinsic pathway:
- Starts with FAS ( trimeric death receptor) and Fas ligand. Trimeric Fas ligand binds trimeric Fas receptor
- The death domains on the cytosolic tails of Fas bind intracellular death domain adaptor proteins (FADD), which then binds initiator caspases (primarily Caspase-8) forming a DEATH INDUCING SIGNALING COMPLEX (DISC).
- DISC allows dimerization and activation of initiator caspases, which cleaved their partners, which are then released to activate executioner caspases and induce apoptosis.
What is the DISC? what are its components?
DISC- Death inducing signaling complex composed of initiator caspase (caspase 8), FADD and Fas death receptor. This complex helps dimerize initiator caspases, prepare for cleavage and activate executioner for apoptosis.
Describe the structure of death receptors. also discuss what kind of family these receptors belong to as well as their ligands.
Death receptors are transmembrane proteins that contain an extracellular ligand-binding domain, a single transmembrane domain, and an intracellular death domain.
These death receptors belong to TUMOR NECROSIS FACTOR RECEPTOR (TNFR) family. Their ligands belong to TNF Family of signaling factors.
ligands do not float freely in cell.
What kind of structures are both death ligand and death receptor. What occurs when ligand binds to receptor?
Both the death ligand and death receptor are TRIMERIC structures.
Binding of ligand to receptor will alter conformation of receptor, so that it binds a DEATH DOMAIN ADAPTOR protein (FADD), which recruits and activates initiator caspase (caspase 8), triggering caspase cascade that leads to death.
Describe the pathology of disease ALPS (autoimmune lymphoproliferative syndrome).
ALPS- is associated with dominant mutations in death receptor FAS (include point mutation and terminal truncations).
In individuals heterozygous for mutations, lymphocytes do NOT die at their normal rate and accumulate (hence lymphocyte proliferation)
Describe the series of human diseases that have either too much or too little apoptosis as a major factor.
- Heart attacks and strokes- many cells die by necrosis due to ischemia (lack of blood supply), but some also die by apoptosis (receive damage signals)
- Autoimmune disease- caused by mutations in Fas death receptor or Fas ligand which leads to overproduction of lymphocytes and a breakdown of self-tolerance.
- Neurodegenerative diseases- like Alzheimer’s, Parkinson’s, Huntington’s diseases and ALS: cells die due to oxidative stress, perturbed calcium homeostasis and mitochondrial dysfunction.
- Cancer: mutations in Bc12 lead to B-cell Lymphoma: p53 gene is mutated or inhibited in more than half of cancers, thus blocking signal from DNA damage to apoptotic pathway.
Which anti-cancer drugs aid in prevention of the blocking of apoptosis and where are they bound? Which protein blocks apoptosis?
Anti-cancer drugs like ABT-737 inhibit the anti-apoptotic Bc12 family proteins (they prevent apoptosis)
This ABT-737 drug binds to anti-apoptotic Bc12 family proteins like BC1XL, and prevent them from blocking apoptosis.
The drug will bind to Bc1XL within long hydrophobic pocket of Bc1XL (where pro-apoptotic BH3 only proteins bind).
Describe the three types of extracellular signaling molecules and their functions.
Extracellular signaling molecules:
- Survival factors- block apoptosis
- mitogens- promote cell entry into S phase by overcoming intrinsic inhibition of cell cycle.
- Growth factors- stimulate growth in cell size and mass by promoting biosynthesis and inhibiting degradation.
Why do cells compete for survival factors? provide an example.
Cells compete for limited amounts of survival factors produced by other cells to prevent their apoptosis to control tissue development and maintenance.
Ex: normal overproduction of nerve cells in developing mammalian CNS makes nerves compete for survival factors (limited supply) that are secreted by target cells that they connect to .
Nerve cells that die must have active a default death pathway that must be inhibited by survival signal for them to survive.
What is the role of extracellular survival factors in apoptosis?
Extracellular survival factors may STIMULATE TRANSCRIPTION of anti-apoptotic Bc12 protein which leads to blocking of apoptosis.
What is the difference between growth factor and mitogen. What are their similarities?
Growth factor and mitogens DIFFER in the effect each have on CELL BEHAVIOR.
mitogen- cause the cell to replicate, and stimulate cell division
Growth factor- causes cells to grow and cell to become larger; stimulate cell proliferation
Growth factor and mitogens are both extracellular signals.
What are myoblasts and where are they located? What is their function.
Myoblasts (aka Satellite cells) are muscle stem cells in adult muscle.
Myoblasts- dividing cell that can produce muscle; aka satellite cells, they receive signals to inhibit over-proliferation.
What is myostatin and its function?
Myostatin- extracellular signaling molecule that does opposite of mitogen. Myostatin PREVENTS cell from dividing AND becoming MUSCLE.
Muscle fibers secrete myostatin, which is a TGF beta family member, in order to inhibit proliferation and differentiation of myoblasts.
What cellular structure secretes myostatin, and for what use? What kind of molecule is myostatin? What happens to mice who lack myostatin? As well as cattle with mutation in myostatin gene?
Muscle fibers secrete myostatin, which is a TGF beta (transforming growth factor) family member, in order to inhibit proliferation and differentiation of myoblasts.
mice that LACK myostatin have muscles 2-3x than normal.
Cattle with mutations in myostatin gene are double-muscled.
Describe the evolution of multicellularity. How do cells specialize in their functions?
Cells in the human body have lost capacity for independent survival. instead, cells are members of cohesive and integrated organism.
Each cell type is highly specialized, each having particular biochemistry, behaviors, shape, and arrangement that serve the needs of the body as whole.
