Chapter 13: Biochemical Signaling Flashcards
Intercellular signals coordinate metabolic activities through complex biochemical signaling
systems. Intercellular signals are mediated by chemical messengers known as
hormones
that specifically binds a
hormone or other ligand
receptor protein
a mechanism for transmitting the ligand-binding event to the cell
interior
ligand
chemical changes catalyzed by what
kinases and phosphatases
in which a succession of events that each depend on the previous one amplifies the signal
enzyme cascades
Control Fuel Metabolism
Pancreatic Hormone
examples of Pancreatic Hormone
glucagon and insulin
what is the stimuli for the release of insulin
high blood glucose concentrations.
what is the stimuli for the release of glucagon
low blood glucose concentrations.
It stimulates the liver to release glucose through the breakdown of glycogen (glycogenolysis) and the synthesis of glucose (gluconeogenesis) from noncarbohydrate
precursors.
Glucagon
stimulates muscle, liver, and adipose cells to store glucose for later use by
synthesizing glycogen, protein, and fat.
Insulin
It also stimulates adipose tissue to release fatty acids through lipolysis.
Glucagon
hormone of the adrenal gland
epinephrine (adrenalin)
It can stimulate glycogenolysis, gluconeogenesis, lipolysis in adipose tissue, the relaxation of smooth (involuntar muscle in the bronchi and in the blood vessels supplying the
skeletal (voluntary) muscles, and increased heart action
epinephrine (adrenalin)
is allosterically controlled by the effectors AMP , A TP , and G6P and is mostly in the T state under
physiological conditions.
phosphorylase beta
is unresponsive to these
effectors and is mostly in the R state unless there is a high level of glucose.
phosphorylase alpha
Insulin and growth factor bind to receptors whose C-terminal domains have what kind of activity
tyrosine kinase activity
Upon binding insulin, the cytoplasmic
protein tyrosine kinase domains get what?
phosphorylated on specific T yr residues
This autophosphorylation activates the what so that it can phosphorylate other protein substrates
PTK
will then relay signals to their
targets
Kinase cascades
SH2-containing proteins that interact
with the insulin receptor substrates
some are kinases,
some are
phosphatases,
and some are GTPases that are
therefore known as G proteins.
When insulin activates the what, the result is an increase in protein
synthesis that supports cell growth and differentiation
Ras signaling pathway
a response consistent with
insulin’s function as a signal of fuel abundance.
differentiation
How a cell prevents inappropriate cross talk between closely related signaling pathways
scaffold proteins
that bind some or all of the
component protein kinases of a particular signaling cascade so as to ensure that the protein
kinases of a given pathway interact only with one another.
scaffold proteins
Intracellular signals must be “turned off” when?
after the system has delivered its message so that the system can transmit future messages
their activities are balanced by the activities of protein phosphatases that hydrolyze the phosphoryl groups
attached to Ser, Thr, or T yr side chains and thereby limit the effects of the signal that activated the kinase.
protein kinases
is caused by the Yersinia bacteria
Bubonic Plague (the flea-transmitted “Black Death”)
Bacteria lack what?
protein tyrosine kinases
are members of the superfamily of regulatory GTPases.
share common structural motifs that bind guanine nucleotides and catalyze the hydrolysis of GTP .
participate in signal
transduction systems
Heterotrimeric G proteins
transduction systems that consist of three major components
- G protein–coupled receptors
- Heterotrimeric G proteins
- Adenylate cyclase. A
catalyzes the synthesis of cAMP from ATP .
Adenylate cyclase
what is Adenylate cyclase main target In eukaryotic cells,
protein kinase A (also known as cAMP-dependent protein kinase
an enzyme that phosphorylates specific Ser or Thr residues of numerous cellular proteins.
protein kinase A (also known as cAMP-dependent protein kinase),
is a second messenger, that
is, it intracellularly transmits the
signal originated by the
extracellular ligand.
cAMP
bind peptide hormones, odorant (having an odor) and tastant (having a taste) molecules, eicosanoids. The importance of these receptors is also evident in the fact that some 60% of
the therapeutic drugs presently in use target them
The G protein–coupled receptors include the glucagon receptor, and a host of other proteins
In the absence of what , protein kinase A is an inactive heterotetramer of two regulatory and two catalytic subunits, R2C2.
cAMP
binds to the regulatory subunits to cause the dissociation of active catalytic monomers.
cAMP
The targets of protein kinase A include
enzymes involved in glycogen metabolism.
when what binds to the β-adrenoreceptor of a muscle cell, the
sequential activation of this system leads to the activation of glycogen phosphorylase,
thereby making glucose-6-phosphate available for glycolysis.
epinephrine
Each step of a signal transduction pathway can potentially be
regulated
In addition, reactions catalyzed by protein kinase A are reversed by protein
Ser/Thr
phosphatases.
Many drugs and toxins exert their effects by modifying components of the what
adenylate cyclase system.
The effect of G protein activation is short-lived, because of what
G alpha is also a GTPase that
catalyzes the hydrolysis of its bound GTP to GDP + Pi, although at the relatively sluggish rate of 2 to 3 min–1
When GTP is bound to G alpha, its phosphate group promotes conformational changes
causing G alpha to do what
dissociate from G beta γ.
antagonizes adenosine receptors causing an increase in cAMP concentration
caffeine
Deadlier effects result from certain bacterial toxins that interfere with
heterotrimeric G
protein function.
The toxin released by the bacterium causing cholera triggers what
massive fluid loss of over a liter per hour from diarrhea. Victims die from dehydration unless their lost
water and salts are replaced
causes the transfer of the ADP-ribose moiety of NAD to an Arg residue of Gs protein. The modified G protein constantly activates adenylyl cyclase results in an overproduction of cAMP
Cholera toxin
requires a receptor, a heterotrimeric G protein, a specific kinase, and a phosphorylated glycerophospholipid that is a minor component of the plasma membrane. It
Phosphoinositide pathway
Phosphoinositide pathway produces what?
inositol-1,4,5-
trisphosphate (IP3),
Ca2+
1,2-diacylglycerol (DAG)
The sense of taste in vertebrates reflects what?
the activity of neurons clustered in taste buds on
the surface of the tongue.
