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Capítulo 8
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1. Hemoglobin (the globin polypeptides that make up the protein) and ribosomal proteins.

2. The cells would be expected to secrete lysosomal enzymes into the medium. If the cells were incubated with 32 P-phosphate, the label would not be expected to appear in lysosomal enzymes as it would in control cells. Golgi fractions prepared from the cells should lack the enzyme N -acetylglucosamine phosphotransferase, which transfers the phosphorylated sugar from UDP to a mannose receptor.

3. Endoplasmic reticulum; medial/trans golgi cisternae; trans Golgi cisternae/TGN

4. The peroxisomal proteins contain specific signals (PTSs) that mediate import via interaction with a peroxisome-protein receptor. NADH cannot trigger this response. The channel is not simply an open pore allowing any substance through, but is likely gated and opened by the PTS receptor.

5. The RER would have the SRP receptor and protein-translocating channel proteins. The SER would have a calcium pump (Ca 2+ -ATPase), glucose 6-phosphatase, and cytochrome P 450s.

6. The process can be studied in embryos where it occurs for the first time. Alternatively, cells could be stimulated hormonally or with agents that increase intracellular calcium to provoke granule discharge.

7. They are mutant cells that lack the glycosyltransferases that add sugars onto the mannose residues.

8. While autoradiography is useful in determining whether, for example, secretory proteins are synthesized on the RER or the Golgi complex, it lacks the resolution required to determine, for example, which side of a membrane a protein is synthesized on. Thicker sections will have radioactive isotopes located at a greater distance beneath the covering emulsion. As a result, the path of the particles will occur at a wider angle and strike the emulsion at a site that is farther away from the point in the emulsion that is directly above the particle source.

9. [ 3 H]leucine in the cytosol and the RER; [ 3 H]sialic acid in the trans end of the Golgi complex; [ 3 H]mannose in the rough ER; [ 3 H]choline in the rough ER; [ 3 H]glucuronic acid in the Golgi complex; [ 3 H]pregnenolone in the SER; [ 3 H]rhamnose in the Golgi complex.

10. A pancreatic acinar cell because it is the only one of three that engages in large-scale secretion. Secretory activity requires exocytosis during which the surface area of the plasma membrane is increased. Bulk-phase endocytosis provides a mechanism to internalize excess plasma membrane.

11. To the extracellular side. The cisternal (luminal) side of the Golgi becomes the inner (luminal) side of secretory vesicles and, following exocytosis, becomes the external side of the plasma membrane.

12. Plasma membrane; SER; RER; lysosome; plant vacuole; plasma membrane; TGN (or other membranes of the biosynthetic pathway); cytosol.

13. Throughout the entire biosynthetic pathway and the extracellular medium.

14. The surface of the RER would be smooth not unlike the SER

15. Binding to a ligand would change the conformation of the cytosolic domain of the receptor causing it to bind to adaptors on the inner surface of the plasma membrane.

16. One way would be to treat the section with gold-labeled antibodies against one of the lysosomal enzymes.

17. Chloride ions normally move passively through the chloride channels of the endosomal membrane, which prevents the buildup of an electric potential across the membrane that would counteract the continued pumping of protons. Without these channels, the pump cannot generate as high a proton gradient as it would otherwise, so that the endosomal lumen cannot become as acidic as would normally be the case.

18. The red fluorescence indicates the location of COPI proteins, which are present on vesicles carrying ER resident proteins back to the ER. Consequently, one would expect COPI proteins to appear at lower levels in the ER membranes.







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