A 5-month-old boy is brought to his pediatrician because his parents have noticed that he has very restricted joint movement. He was born at home without prenatal care, but they say that he appeared healthy at birth. Since then, they say that he doesn't seem to move very much and is hard to arouse. Physical exam reveals coarse facial structures and hepatosplenomegaly. Radiography reveals skeletal malformations, and serum tests show high plasma levels of lysosomal enzymes. The production of which of the following substances will most likely be disrupted in this patient?
AGlucocerebroside
BMannose-6-phosphate
CHeparan sulfate
DCeramide
An investigator is studying the function of the endoplasmic reticulum in genetically modified lymphocytes. A gene is removed that facilitates the binding of ribosomes to the endoplasmic reticulum. Which of the following processes is most likely to be impaired as a result of this genetic modification?
AProduction of secretory proteins
BNeutralization of toxins
CUbiquitination of proteins
Dα-Oxidation of fatty acids
ESynthesis of ketone bodies
A scientist is studying a protein that is present on the plasma membrane of cells. He therefore purifies the protein in a lipid bilayer and subjects it to a number of conditions. His investigations show that the protein has the following properties: 1) It is able to change ion concentrations across the membrane without addition of ATP to the solution. 2) Its activity increases linearly with substrate concentration without any saturation even at mildly supraphysiologic conditions. 3) In some states the protein leads to an ion concentration change; whereas, it has no effect in other states. 4) Changing the electrical charge across the membrane does not affect whether the protein has activity. 5) Adding a small amount of an additional substance to the solution reliably increases the protein's activity. These findings are consistent with a protein with which of the following functions?
AMaintenance of resting sodium and potassium concentrations
BTransporting water in the collecting duct of the kidney
CReabsorption of glucose in the proximal kidney tubule
DMediating neuronal to muscle end plate communication
ECausing depolarization during action potentials
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