Chapter 8

Which, if any, of the following polypeptides would be expected to lack a signal peptide: collagen, acid phosphatase, hemoglobin, ribosomal proteins, glycophorin, proteins of the tonoplast?

In what cellular compartment would a glycoprotein be expected to have its greatest mannose content? its greatest \(N\) -acetylglucosamine content? its greatest sialic acid content?

It was noted on page 316 that peroxisomes are able to import folded proteins. Yet, these same organelles are impermeable to relatively small molecules such as NADH and acetyl-CoA. How is it possible to be permeable to one and not the other?

Name two proteins you would expect to find as integral components of the RER membrane that would be absent from the SER? Name two proteins of the SER that would not be present in the RER?

Suppose you wanted to study the process of regulated secretion in a cell that lacked mature secretory granules, that is, vesicles containing secretory material that was ready to be discharged. How might you obtain a cell that lacked such granules?

Autoradiography depends on particles emitted from radioactive atoms striking a photographic emulsion that lies on top of the tissue section. When the emulsion is developed, the site where the particle struck the emulsion appears as a silver grain, as in Figure \(8.3 a .\) How do you think the thickness of the section might affect the resolution of the technique, that is, the ability to locate the precise site in the cell where radioactivity is incorporated?

In which part of a cell would you expect the following compounds to be first incorporated: \(\left[^{3} \mathrm{H}\right]\) leucine, \(\left[^{3} \mathrm{H}\right]\) sialic acid \(\left[^{3} \mathrm{H}\right]\) mannose, \(\left[^{3} \mathrm{H}\right]\) choline, \(\left[^{3} \mathrm{H}\right]_{8}\) lucuronic acid (a precursor of GAGs), \(\left[^{3} \mathrm{H}\right]_{\text {pregnenolone }}(\) a precursor of steroid hormones), \(\left[^{3} \mathrm{H}\right]\) rhamnose in a plant cell (rhamnose is a precursor of pectins \() ?\)

Which of the following cells would you expect to be engaged most heavily in bulk-phase endocytosis: (a) an erythrocyte, (b) a pancreatic acinar cell, (c) a skeletal muscle cell? Why?

Would you expect the properties of the cisternal side of Golgi membranes to be more similar to the extracellular or cytosolic side of the plasma membrane? Why?

Which compartment(s) of a cell is associated with each of the following: clathrin, calcium ions in a skeletal muscle cell, dolichol phosphate, ribonuclease and lipase, digitalis, LDL receptors, COPI proteins, COPII proteins, unbound SRPs?

If you were to add a drug that interfered with the ability of ribosomes to bind to mRNA, what effect would this be expected to have on the structure of the RER?

Not all receptors that carry out RME are located in coated pits prior to binding ligand, yet they too become concentrated in coated pits prior to internalization. How do you suppose the binding of a ligand to a receptor would cause it to become concentrated into a coated pit?

Studies of a rare inherited disorder, Dent's disease, revealed that these individuals lacked a chloride ion channel in the endosomes of the cells of their kidney tubules. These patients suffered from a variety of symptoms that suggested that their endosomal compartments were not as acidic as those of normal individuals. How do you suppose that a defect in a chloride channel could account for this condition?