43.The answer is d.(Alberts, pp 769–783. Junqueira, pp 29–30, 32. Ross
and Pawlina, pp 52–54.)The mitochondrial electrochemical gradient is
established by a proton pump. The pump is located in the inner mem-
brane, associated with the respiratory chain and ATP synthase. The imper-
meability of the inner membrane to protons causes an osmotic and
electrochemical gradient to develop. Mitochondria produce energy that the
cell uses in transport and other energy-dependent processes. Cellular
energy is stored as ATP, which is synthesized by the phosphorylation of
ADP by ATP synthase (answer a).Mitochondria use the electron-transport
(respiratory) chain that transfers energy from NADH to O 2 (answer b).As
electrons released by oxidation of substrate in the matrix flow down the
respiratory chain, hydrogen ions are pumped into the intermembrane
space(answer c).Protons in the matrix drive ATP synthase in a mecha-
nism similar to that of a waterwheel. ATP synthase, therefore, couples
oxidative transport through the electron-transport (respiratory) chain with
energy storage (ATP). ATP is not transported out of the matrix compart-
ment by a specific transporter (answer e).
44.The answer is d.(Alberts, pp 702–703. Mole, pp 70–76.)The patient is
suffering from the infantile form of Batten’s disease, neuronal ceroid lipo-
fuscinoses, in which there is a build-up of lipofuscin because of the
absence of specific lysosomal enzymes. Dolichol is normally associated
with N-linked glycosylation in the rough endoplasmic reticulum (RER) an
en blocmethod in which dolichol is added to the protein. O-linked glyco-
sylation occurs in the Golgi, by a mechanism involving oligosaccharide
(glycosyl) transferases rather than en blocwith dolichol (answers b and c).
N-linked oligosaccharides are the most common oligosaccharides found in
glycoproteins and contain sugar residues linked to the NH 2 amide nitrogen
of asparagine. O-linked oligosaccharides have sugar residues linked to
hydroxyl groups on the side chains of serine and threonine. The diversity
in oligosaccharides is produced by selective removal of glucose and man-
nose from the core oligosaccharide. This trimming process begins in the
RER before reaching the Golgi, where the final mannose-residue trimming
occurs. Sulfation (answer a)and protein sorting (answer e)are carried out
in the Golgi apparatus, but do notinvolve dolichol.
45.The answer is b.(Alberts, pp 687–688. Ross and Pawlina, p 55. Junquiera,
p 40.)The child suffers from Zellweger syndrome, in which peroxisomes are
Cell Biology: Cytoplasm Answers 119