Apoptosis Flashcards
apoptosis
when normal cells die
necrosis
where injury was extreme and sudden: ischemia following occlusion of a major artery, physical or chemical trauma, or overwhelming infection.
In necrosis, At the stage called “high-amplitude swelling”
it can no longer maintain its ionic gradients or oxidative phosphorylation, and the cell runs out of energy.
Necrosis is
intensely proinflammatory.
The defining morphological feature of apoptosis is a
collapse of the nucleus
Early in apoptosis cells ______, and the result is a
shrink remarkably, losing about a third of their volume in a few seconds.
peculiar, vigorous “boiling” action of the plasma membrane, which has been called zeiosis.
the goal of all the
morphological changes of apoptosis is
to ensure that
the apoptotic cell gets taken up by a healthy cell, before it has had a chance to spill its dangerous contents.
why is necrosis so inflammatory?
Lysis releases the cell’s intracellular contents into the extracellular, these internal lipids, proteases, and small molecules are intensely inflammatory.
They attract white cells, primarily macrophages, from around the body.
The effect of the inflammatory process is
debris removal, injury resolution, and, if the stroma has been damaged, scar formation.
in apoptosis, chromatin,
becomes supercondensed, appearing as crescents around the nuclear envelope and, eventually, spherical featureless beads.
zeiosis
By this action the apoptotic cell usually tears itself apart into apoptotic bodies, some of which contain chromatin.
Apoptosis is also accompanied by
changes in the plasma membrane, the most obvious of which involves the phospholipid phosphatidylserine (PS).
All the PS in a normal plasma membrane is confined to the______
inner leaflet of the lipid bilayer
flippase ensures that any
PS molecule that strays to the outer leaflet is quickly returned.
Soon after apoptosis begins, the distribution of PS becomes
equal on both sides of the membrane, by a “scrambling” mechanism involving, as you’d guess, “scramblase.”
This means that PS is now exposed on the cell’s exterior surface.
Phagocytic cells have receptors for PS, and
recognize, bind to, and ingest cells that have committed to the apoptotic pathway, consuming them while they are still alive.
In this way the apoptotic cell never has a chance to lyse and release inflammation-causing molecules to the extracellular space.
a macrophage that recognizes a cell as apoptotic
does not become activated.
So the removal of apoptotic cells
physiological and silent,
______ are the most radiation-sensitive cells in the universe;
Lymphocytes
0.05 grey will kill one by apoptosis, while it takes 150 grey to kill a macrophage.
If lymphocytes are exposed to radiation in the presence of a drug that blocks transcription, they
do not die.
low-dose radiation does not kill lymphocytes;
it induces them to kill themselves.
if one cell type has “death genes,” then
all cells in the body do, since they share the same genome.
any cell in the body could be made to undergo apoptosis if
we could understand how to get it to turn on these genes, and any cell that intended to die might be prevented from doing so by a reverse strategy.
morphogenetic death determines
the final shape of body parts and organs.
Apoptosis: In the nervous system,
many more cells develop than the organism needs; those that form the correct contacts at the correct time are bathed in survival factors by the target they have innervated; if not, they are dispensable.
Apoptosis In limbs,
the death by apoptosis of cells between the digits gives the final form to fingers and toes.
Indeed, even the formation of as precise a structure as the brain depends on a
Darwinian-style selection of cells that have chanced to make the best connections. Other local conditions could determine cell survival.
cell shape, as influenced by the local tissue geometry, affects
whether a cell will live or die.
Mitosis is estimated to occur
25 million times a second in an adult human.
In a steady-state system whenever a cell in a particular compartment divides,
another must die, or else the size of the compartment will change.
But using the 1 mitosis = 1 apoptosis assumption we find that, in an average adult,
2 x 1012 cells die every dayan incredible number.
for cancer progression, mutations that
inhibit death may be just as important as those that stimulate growth.
death controlled by
pro- and anti-apoptotic Bcl-2 factors
two pathways for apoptosis:
- intrinsic: from the inside, typically mitochondria
2. extrinsic: cytotoxic T cells
