of the contents of secretory vesicles, facilitates breakdown of the contents of
phagosomes and lysosomes, and is involved in the cleavage of prohormones
to their active forms (e.g., proinsulin to insulin). The acidification process
functions through a vacuolar H+(proton) pump that is present in the mem-
branes of most endocytic and exocytic vesicles, including those of the
phagosomes, lysosomes, secretory vesicles, and some compartments of the
Golgi. Ribosomes are not dependent on a proton pump mechanism and are,
therefore, less sensitive to chloroquine. Note that pancreatic beta cells syn-
thesize insulin. Proinsulin is split into C-peptide +insulin in secretory vesi-
cles(answer b). In vivo, C-peptide release can be used to measure
production of insulin by a patient’s pancreatic beta cells. This is particularly
useful in patients who are receiving insulin. Glucagon is synthesized by
alpha cells (answer d),and amylase is an exocrine pancreatic product pro-
duced by the acinar cells (answer e).Gene and message expression and
message stability are also nottargets for chloroquine (answers d and e).
48.The answer is b.(Alberts, pp 770–774. Junqueira, pp 30–33.)The struc-
ture labeled B is the inner membrane of the mitochondrion, which is highly
impermeable to small ions because of the presence of cardiolipin. The inner
membrane contains the proteins required for the oxidative reactions of the
respiratory transport chain; it is the location of the cytochromes, dehydroge-
nases, and flavoproteins including cytochrome C as well as the transmem-
brane complex (ATP synthase) that is responsible for ATP synthesis. The inner
membrane is folded into convolutions called cristae. The number of cristae is
directly related to the metabolic activity of the cell. The elementary particles
that have been identified on the cristae are composed primarily of ATP syn-
thase complexes. The patient in the vignette is suffering from Leigh’s Disease
(Subacute Necrotizing Encephalomyelopathy), a generalized (systemic) form
of Cytochrome C oxidase (COX) Deficiency, characterized by progressive
degeneration of the brain and dysfunction of the heart, kidneys, muscles, and
liver. Symptoms include loss of acquired motor skills and loss of appetite,
vomiting, irritability, and/or seizure activity. As Leigh’s Disease progresses,
symptoms include generalized weakness; loss of muscle tone (hypotonia);
and/or episodes of lactic acidosis with lactate higher in the CSF than the
blood. The region labeled Ain the electron micrograph of the mitochondrion
is the mitochondrial matrix, or intercristal space. The matrix contains the cir-
cular DNA of the mitochondrial genome. Most mitochondrial proteins are
encoded for by nuclear DNA, but small proportions are encoded within the
Cell Biology: Cytoplasm Answers 121