Study Set Content:
In all cases, the crucial step is stimulation of membrane
enzymes:
Phospholipase C (PLC)
Phosphatidylinositol-4,5-biphosphate (PIP 2)
– is confined to the membrane,
where it activates a phospholipid and calcium-sensitive
protein kinase called protein kinase C.
Diacylglycerol (IDAG)
is
water-soluble and diffuses through the cytoplasm to
trigger the release of Ca2+ by binding to ligand-gated
calcium channels in the limiting membranes of internal
storage vesicles.
Inositol-1,4,5-trisphosphate (IP3 or InsP3)
Elevated cytoplasmic Ca2+ concentration resulting from IP 3-
promoted opening of these channels promotes the binding of Ca2+
to the calcium-binding protein
calmodulin,
Elevated cytoplasmic Ca2+ concentration resulting from IP 3-
promoted opening of these channels promotes the binding of Ca2+
to the calcium-binding protein calmodulin, which regulates
activities of other enzymes, including
calcium-dependent protein
kinases.
has established signaling roles in only a few cell types.
C. Cyclic Guanosine Monophosphate (cGMP)
In(blank), the cGMP-
based signal transduction mechanism closely parallels the cAMP-
mediated signaling mechanism.
intestinal mucosa and vascular smooth muscle
Ligands detected by cell-surface receptors stimulate membrane-
bound (blank) to produce cGMP, and
guanylyl cyclase
Ligands detected by cell-surface receptors stimulate membrane-
bound guanylyl cyclase to produce cGMP, and cGMP acts by
stimulating a
cGMP-dependent protein kinase.
The actions of cGMP in these cells are terminated by
enzymatic degradation of the
cyclic nucleotide
The actions of cGMP in these cells are terminated by
enzymatic degradation of the cyclic nucleotide and by
dephosphorylation of kinase substance.
The other mechanism mediates responses to
nitric oxide (NO),
The other mechanism mediates responses to nitric oxide (NO),
which is generated in vascular endothelial cells in response
to natural vasodilator agents such as
acetylcholine and
histamine.
After entering the target cell, nitric oxide binds to and
activates a
cytoplasmic guanylyl cyclase.
(blank) and (blank)signaling pathways
oppose one another in some cells and are complementary
in others.
Calcium-phosphoinositide ,cAMP
For example, (blank) that contract smooth
muscle act by IP3-mediated mobilization of Ca2+,
Vasopressor agents
For example, Vasopressor agents that contract smooth
muscle act by IP3-mediated mobilization of Ca2+, whereas
agents that relax smooth muscle often act by elevation of
cAMP
Almost all second messenger signaling involves
reversible
phosphorylation,
Almost all second messenger signaling involves reversible
phosphorylation, which performs two principal functions in
signaling:
Amplification
Flexible Regulation
powerfully amplifies the initial regulatory signal by recording
a molecular memory that the pathways have been activated,
Amplification
