Essential Cell Biology 5th edition

Questions
571
KEY TERMS
adaptation GTP-binding protein phosphoinositide 3-kinase
adenylyl cyclase hormone (PI 3-kinase)
Ca 2+ /calmodulin-dependent inositol 1,4,5-trisphosphate phospholipase C
protein kinase (CaM-kinase) (IP 3 ) protein kinase
calmodulin inositol phospholipid protein kinase C (PKC)
cell signaling intracellular signaling pathway protein phosphatase
cyclic AMP ion-channel-coupled receptor Ras
cyclic-AMP-dependent local mediator receptor
protein kinase (PKA) MAP kinase receptor serine/threonine kinase
diacylglycerol (DAG) MAP-kinase signaling module receptor tyrosine kinase (RTK)
enzyme-coupled receptor molecular switch serine/threonine kinase
extracellular signal molecule monomeric GTPase signal transduction
G protein neurotransmitter steroid hormone
G-protein-coupled receptor nitric oxide (NO) tyrosine kinase
(GPCR)
nuclear receptor
QUESTIONS
QUESTION 16–8
Which of the following statements are correct? Explain your
answers.
A. The extracellular signal molecule acetylcholine has
different effects on different cell types in an animal and
often binds to different cell-surface receptor molecules on
different cell types.
B. After acetylcholine is secreted from cells, it is long-lived,
because it has to reach target cells all over the body.
C. Both the GTP-bound α subunits and nucleotide-free
βγ complexes—but not GDP-bound, fully assembled
G proteins—can activate other molecules downstream of
GPCRs.
D. IP 3 is produced directly by cleavage of an inositol
phospholipid without incorporation of an additional
phosphate group.
E. Calmodulin regulates the intracellular Ca 2+
concentration.
F. Different signals originating from the plasma membrane
can be integrated by cross-talk between different signaling
pathways inside the cell.
G. Tyrosine phosphorylation serves to build binding sites
for other proteins to bind to RTKs.
QUESTION 16–9
The Ras protein functions as a molecular switch that is set
to its “on” state by other proteins that cause it to release
its bound GDP and bind GTP. A GTPase-activating protein
helps reset the switch to the “off” state by inducing Ras
to hydrolyze its bound GTP to GDP much more rapidly
than it would without this encouragement. Thus, Ras works
like a light switch that one person turns on and another
turns off. You are studying a mutant cell that lacks the
GTPase-activating protein. What abnormalities would you
expect to find in the way in which Ras activity responds to
extracellular signals?
QUESTION 16–10
A. Compare and contrast signaling by neurons, which
secrete neurotransmitters at synapses, with signaling carried
out by endocrine cells, which secrete hormones into the
blood.
B. Discuss the relative advantages of the two mechanisms.
QUESTION 16–11
Two intracellular molecules, X and Y, are both normally
synthesized at a constant rate of 1000 molecules per second
per cell. Molecule X is broken down slowly: each molecule
of X survives on average for 100 seconds. Molecule Y is
broken down 10 times faster: each molecule of Y survives
on average for 10 seconds.
A. Calculate how many molecules of X and Y the cell
contains at any time.
B. If the rates of synthesis of both X and Y are suddenly
increased tenfold to 10,000 molecules per second per cell—
without any change in their degradation rates—how many
molecules of X and Y will there be after one second?
C. Which molecule would be preferred for rapid signaling?