Understanding the Nucleus - GRE Subject Test: Biology

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Question

How are proteins imported into the nucleus?

Answer

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.

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Question

Which of the following is true regarding the nucleus?

Answer

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.

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Question

What provides structural support for the nucleus and binds chromatin?

Answer

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.

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