GRE Subject Test: Biology › Understanding the Nucleus
What provides structural support for the nucleus and binds chromatin?
Lamina
Nucleolus
Nuclear pores
Cytoskeleton
Nuclear envelope
The correct answer is lamina. This is a fibrous network of filaments within the nucleus that provides architectual support similar to the cytoskeleton. Chromatin also is held in place by association with the lamina.
How are proteins imported into the nucleus?
With the assistance of special proteins known as importins
Passive diffusion through nuclear pore complexes
Translocation through nuclear pore complexes while they are being translated by membrane-bound ribosomes
Proteins are only exported from the nucleus
Nuclear import and export is tightly regulated by importin and exportin proteins. These proteins interact with target proteins to carry them into or out of the nucleus, respectively. Proteins cannot passively diffuse into the nucleus and they are not translocated into the nucleus during translation.
Which of the following is true regarding the nucleus?
All of these answers
The nucleus is studded with many openings called nuclear pore complexes
The nucleus is the site of assembly for ribosomal subunits
The nucleus is surrounded by multiple membranes
All of these choices are correct regarding the nucleus. Nuclear pore complexes are incredibly important for regulating nuclear import and export. Ribosomal subunits are assembled in the nucleolus, which is a portion of the nucleus. The nucleus is covered by two lipid bilayers, which constitute the nuclear envelope.