Question

You purified fragments of nuclear envelope from human fibroblasts by biochemical fractionation. You first decide to use electron microscopy to test for the presence of the nuclear lamina on these envelope fragments. Which of the following structures would suggest the presence of the nuclear lamina?

An organized meshwork of ~ 10 nm fibers
Large pores that span through both nuclear membranes
Two phospholipids bilayers
"Little bumps", presumably membrane proteins, at the surface of the inner membrane
~300 and ~700 nm fibers

In a second set of experiments, you decide to treat the purified nuclear envelope fragments with a solution that disrupts all protein-protein interaction, but that leaves phospholipid bilayers intact. Which of the following proteins would be missing from the nuclear envelope fragments after treatment?

Lamin associated protein 1
Lamin associated protein 2
Lamin-B
Lamin A
The lamin B receptor

Answer 1

Answer

1. The nuclear lamina is a network of fibers inside the nucleus. It is a dense structure which is about 30 to 100 nm thick. When viewed under an electron microscope, a meshwork of lamin A, B, and C indicates the presence of nuclear lamina.

Therefore, the correct answer is option (a).

2. After the nuclear envelop fragments are treated, the lamin A would be missing from the nuclear envelop. Lamin A and C are structural filamentous proteins which are present in the nuclear lamina that surrounds the nucleus. As they are exposed to the outside environment it makes them susceptible to chemical disturbances leading to disruption of protein-protein interactions.

Therefore, the correct answer is option (d).