Chap. 21 Problem 11
Experiments performed with knockout mice indicate that neurons in the brain
and other tissues die by apoptosis in animals in which neurotrophins or their
receptors are inactivated (Fig. 21.36, skin & muscle). This indicates that
apoptosis is the default pathway in the absence of trophic factors.
Chap. 21 Problem 12
Apoptosis is a regulated program that
can be induced by withdrawal of trophic
factors, which signal cells to stay alive,
or by receipt of death signals like tumor
necrosis factor, which trigger apoptosis.
The structural changes that occur during
apoptosis are morphologically distinct
from changes that occur due to cell
death via necrosis (Fig. 21.30). In
necrosis, cells typically burst and release
their contents outside. This damages
surrounding cells and can lead to
inflammation. In apoptosis, cells shrink,
condense, and fragment without the
release of cell contents. Cell fragments
known as apoptotic bodies are later
phagocytosed. Apoptosis proceeds via the
same morphological events regardless of
whether it is triggered by a death signal
or by withdrawal of a trophic factor.
This is because the same intracellular
processes are triggered by the two types
of signaling.
Chap. 21 Problem 16
a) Bad is a pro-apoptotic factor
that is activated in the absence
of trophic factors (Fig. 21.38).
Phosphorylation of Bad in the
presence of a trophic factor
inhibits its pro-apoptotic
activity. Thus, a mutation that
blocks Bad phosphorylation will
cause cells to undergo apoptosis
even in the presence of trophic
factors.
b & c) Cells that overexpress
Bcl-2, an anti-apoptotic factor
should not undergo apoptosis
even in the absence of trophic
factors. Likewise, Bax
mutations that block its
oligomerization should interfere
with apoptosis.
Both b & c types of mutations
could contribute to cancerous
transformation due to the fact
that they block apoptosis even
in the absence of trophic
factors.