of cytosolic proteins. DAG (Bin the figure) activates protein kinase C (so
called because of its Ca^2 +-dependency), which is labeled D.The protein
kinase C phosphorylates (F)specific serine and threonine residues and
may alter gene transcription. In contrast, IP 3 functions to mobilize Ca^2 +by
binding to IP 3 -gated channels in the ER membrane (answer b).The two
intracellular messenger pathways do interact in that elevated Ca^2 +translo-
cates protein kinase C from the cytosol to the inner leaflet of the plasma
membrane. Gi(answer d)is the inhibitory G protein that leads to 5’-AMP
production through the action of phosphodiesterase instead of cAMP. GSis
involved in adenylate cyclase signal transduction (answer e).
59.The answer is b.(Alberts, pp 757–758.)Cirrhosis damages hepatocytes
leading to a reduction in synthesis of serum proteins. The pathway labeled
in the figure as II (C → E) is the constitutive (default) pathway, which is fol-
lowed by proteoglycans, fibronectin, and collagen synthesized by fibrob-
lasts, serum proteins synthesized by hepatocytes (albumin, transferrin and
lipoprotein), and immunoglobulins produced by lymphocytes. The path-
way labeled as I (A → D) differs from constitutive secretion (C → E) in sev-
eral ways. The most important difference is the requirement for a
secretagogue (substance that induces secretion from cells) in the regulated
pathway(answers a and c),which binds to a cell-surface receptor. Secre-
tion in the constitutive pathway is not regulated at the level of second mes-
sengers(answers d and e).Regulated secretion (process I) shows the
recognition of a receptor (B)for its ligand (A),resulting in the release of
secretion in response to the stimulus of secretagogue-receptor binding. The
synthetic processes in the two pathways are then identical until the Golgi.
The vesicles that bud from the Golgi (D)in the regulated pathway are
clathrin-coated and contain a receptor involved in the concentration of
secretory product that normally occurs before release. The constitutive
pathway shuttles proteins such as integral membrane proteins and lipids in
vesicles to the apical and basolateral membranes. The vesicles are nonclathrin-
coated in the constitutive pathway. Exocytosis requires vesicle fusion with
the membrane in both regulated and constitutive pathways. Ras-superfam-
ily GTPases, members of the protein kinase D family and tethering com-
plexes such as the exocyst are involved in constitutive secretion.
60.The answer is e.(Alberts, pp 720–722, 724, 729–730, 744–745.
Junqueira, pp 39, 50.)The child is suffering from inclusion (I)–cell disease.
136 Anatomy, Histology, and Cell Biology