52.The answer is a.(Alberts, pp 742–743, Fig. 13-35. Rubin, pp 785–787.
Kumar, pp 910–911. Kapser, pp 409–410.)The patient in the scenario suffers
from Wilson’s disease in which copper accumulates in the tissues. For exam-
ple, in the liver the mutation in ATP7B prevents translocation of copper from
the cytosol to the late endosome blocking biliary copper excretion via lyso-
somes and resulting in accumulation of copper in the liver. The late endosome
is part of the endocytic pathway. Cargo proteins from the late endosome reach
the lysosome by development into lysosomes, transport to lysosomes via vesi-
cles, or fusion with lysosomes. Clathrin-coated pits and vesicles (answer b)
endocytose and subsequently deliver proteins to the early endosome in the
first stages of the endocytic process. Multivesicular bodies (MVBs) are the
means of transport from early to late endosomes (answer c).The CGN (cis-
Golgi network) receives transitional elements in the form of coatomer-coated
vesicles carrying proteins and lipids from the rough endoplasmic reticulum
and participates in phosphorylation. The remaining Golgi stacks are the cis,
medial,trans, and TGN (trans-Golgi network). The medial compartment is
responsible for the removal of mannose and the addition of N-acetylglu-
cosamine. The transface is responsible for the addition of sialic acid and galac-
tose. The TGN serves as a sorting station for proteins destined for various
organelles (e.g., lyosomes), the plasma membrane, and protein for export
from the cell (answer e).Golgi-derived transport and secretory vesicles bud
off from the TGN. Recycling of receptors occurs from early endosomes to the
plasma membrane (answer d).
53.The answer is d.(Junqueira, pp 34–35.)The predominant organelle in
the transmission electron micrograph is the rough endoplasmic reticulum
(RER). Different proteins display different rates of folding in the ER, and
these rates determine the time required for transport to the cell surface.
Within the ER there are protein chaperones and mechanisms to prevent
aberrant protein folding and to catalyze isomerization of correct covalent
bonds. Frequently, changes in the extracellular environment result in aber-
rant protein folding in the ER as occurs in Alzheimer disease from which
the patient in the vignette suffers. O-linked glycosylation, sorting of pro-
teins and sulfation (answers a, b and c)occur in the Golgi apparatus and
glycogenolysis(answer e)occurs in the smooth endoplasmic reticulum.
Cell Biology: Cytoplasm Answers 125