Chapter 16, Problem 16.7PS

Nuclear Structure and Function. Indicate the implications for nuclear structure or function of each of the following experimental observations.

1. (a) Sucrose crosses the nuclear envelope so rapidly that its rate of movement cannot be accurately measured.
2. (b) Colloidal gold particles with a diameter of 5.5 nm equilibrate rapidly between the nucleus and cytosol when injected into an amoeba, but gold particles with a diameter of 15 nm do not.
3. (c) Nuclear pore complexes sometimes stain heavily for RNA and protein.
4. (d) If gold particles up to 26 nm in diameter are coated with a polypeptide containing a nuclear localization signal (NLS) and are then injected into the cytosol of a living cell, they are transported into the nucleus. If they are injected into the nucleus, however, they remain there.
5. (e) Many of the proteins of the nuclear envelope appear from electrophoretic analysis to be the same as those found in the endoplasmic reticulum.
6. (f) Ribosomal proteins are synthesized in the cytosol but are packaged with rRNA into ribosomal subunits in the nucleus.
7. (g) Treatment of nuclei with the nonionic detergent Triton X-100 dissolves the nuclear envelope but leaves an otherwise intact nucleus.