Molecular Biology of the Cell by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morgan, Martin Raff, Keith Roberts, Peter Walter by by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morg

CHAPTER 15 END-OF-CHAPTER PROBLEMS
887
active (+ P )
inactive (– P)
100
% active
MAP kinase
50
0
(A) POOLED OOCYTES
– +
0.001 0.01 0.1 1 10
progesterone (µM)
(B) INDIVIDUAL OOCYTES
–+
0.03 µM progesterone
0.1 µM progesterone
0.3 µM progesterone
Figure Q15–3 Activation
of frog oocytes
(Problem 15–14).
(A) Phosphorylation
of MAP kinase in
pooled oocytes.
(B) Phosphorylation of
MAP kinase in individual
oocytes. MAP kinase
was detected by
immunoblotting using
a MAP-kinase-specific
antibody. The first two
lanes in each gel contain
nonphosphorylated,
inactive MAP kinase (–)
and phosphorylated,
active MAP kinase (+).
(From J.E. Ferrell, Jr., and
E.M. Machleder, Science
280:895–898, 1998.
With permission from
AAAS.)
Before you crushed the oocytes, you noticed that not all
oocytes in individual dishes had white spots. Had some
oocytes undergone partial activation and not yet reached
the white-spot stage? To answer this question, you repeat
the experiment, Problems but this p15.11/15.18
time you analyze MAP kinase activation
in individual oocytes. You are surprised to find that
each oocyte has either a fully activated or a completely
inactive MAP kinase (Figure Q15–3B). How can an all-ornone
response in individual oocytes give rise to a graded
response in the population?
15–15 Propose specific types of mutations in the gene for
the regulatory subunit of cyclic-AMP-dependent protein
kinase (PKA) that could lead to either a permanently active
PKA or a permanently inactive PKA.
15–16 Phosphorylase kinase integrates signals from the
cyclic-AMP-dependent and Ca 2+ -dependent signaling
pathways that control glycogen breakdown in liver and
muscle cells (Figure Q15–4). Phosphorylase kinase is composed
of four subunits. One is the protein kinase that catalyzes
the addition of phosphate to glycogen phosphorylase
to activate it for glycogen breakdown. The other three subunits
are regulatory proteins that control the activity of the
phosphorylase kinase
inactive
cAMP
Ca 2+
Ca 2+
Ca 2+
phosphorylase kinase
active
Figure Q15–4 Integration of cyclic-AMP-dependent and Ca 2+ -
dependent signaling pathways by phosphorylase kinase in liver and
muscle cells (Problem 15–16).
catalytic subunit. Two contain sites for phosphorylation by
PKA, which is Problems activated by pQ15.04/Q15.04
cyclic AMP. The remaining subunit
is calmodulin, which binds Ca 2+ when the cytosolic
Ca 2+ concentration rises. The regulatory subunits control
the equilibrium between the active and inactive conformations
of the catalytic subunit, with each phosphate and
Ca 2+ nudging the equilibrium toward the active conformation.
How does this arrangement allow phosphorylase
kinase to serve its role as an integrator protein for the multiple
pathways that stimulate glycogen breakdown?
15–17 The Wnt planar polarity signaling pathway normally
ensures that each wing cell in Drosophila has a single
hair. Overexpression of the Frizzled gene from a heatshock
promoter (hs-Fz) causes multiple hairs to grow from
many cells (Figure Q15–5A). This phenotype is suppressed
if hs-Fz is combined with a heterozygous deletion (Dsh Δ )
of the Dishevelled gene (Figure Q15–5B). Do these results
allow you to order the action of Frizzled and Dishevelled
in the signaling pathway? If so, what is the order? Explain
your reasoning.
(A)
hs-Fz / +
+ / +
Figure Q15–5 Pattern of hair growth on wing cells in genetically
different Drosophila (Problem 15–17). (From C.G. Winter et al., Cell
105:81–91, 2001. With permission from Elsevier.)
(B)
P
hs-Fz / +
Dsh ∆ / +
P
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Problems p15.32/15.21
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