BIO 201 Midterm II Review

Lamins are members of a class of structural cytoskeletal proteins called

intermediate filaments. Microtubules and microfilaments are also components of the

proteinaceous cytoskeleton. What is the major difference between lamins on the one

hand and microtubules and microfilaments on the other?

• Lamins are non-force generating and structural only.

• Lamins are found in both animal and plant cells.

• Lamins are located exclusively inside the nucleus.

• Lamins associate with each other; the other proteins act as monomers.

Answer explanation

Lamins are the fibrous proteins that make up the nuclear lamina. The nuclear lamina is a filamentous meshwork that provides structural support to the nucleus. They are a class of intermediate filament proteins similar to the proteins that make up the cytoskeleton.

Depending on size, molecules can enter the nucleus by the process of ____ or ____.

Answer explanation

Proteins must be transported into the nucleus through the nuclear pore complex

because.

• the nuclear pore complex is selective in what it transports.

• nuclear transport receptors are specific for an individual nuclear localization

  signal.

• the energy to drive the transport is generated by cytoplasmic mitochondria.

• there are no tRNAs or ribosomes inside the nucleus.

Both the large and small ribosomal subunits are assembled in the

• cytoplasm

• nucleolus

• nucleus

• ensoplasmic reticulum

Receptor-dependent protein transport into the nucleus requires the recognition of a ______ on the cargo protein

Answer explanation

A major regulatory protein for nuclear import and export of proteins is the small GTPase ____.

Nuclear localization signals are usually short sequences rich in which amino acids?

Answer explanation

Lysine and arginine which is recognized by cytosolic transport proteins (e.g. importins)

In addition to replication factories, the nucleus contains a number of discrete structures, maintained by protein-protein and protein-RNA interactions, that are referred to as ____ _____.

Inactive, condensed chromatin is called heterochromatin.

• TRUE

• FALSE

Answer explanation

Remember the 'topography' of chromatin usually heterochromatin is associated with the lamina near the nuclear envelope and the nucleolus while euchromatin is distributed throughout the nucleus.

What is the function of karyopherins?

Answer explanation

They are nuclear transport receptor proteins.