Question

What will happen to the nucleus if the nuclear pore is blocked? ​

Answer 1

Answer:

One of the defining characteristics of eukaryotic species (like us) is that their nuclei are surrounded by a phospholipid membrane, similar to the membrane that surrounds nearly all cells. Much like the cell membrane, the vast majority of biological macromolecules can't cross the nuclear membrane. Given that transcription of RNA happens exclusively in the nucleus, and translation of proteins happens exclusively in the cytoplasm, a completely impenetrable nuclear membrane poses a severe problem. The other extreme -- no membrane at all -- removes the opportunity to control what goes in and out and how much of it moves.

The nuclear pore complex (or NPC) is a structured ensemble of proteins that sits in the nuclear membrane and enables regulated transit of proteins and RNAs between the nucleus and cytoplasm. You can essentially think about it as having three parts: the pore itself (in yellow in the image below), the cytoplasmic regulatory face (in blue below), and the nuclear regulatory face (in red).

There are a lot of different transport pathways that push biomolecules through the NPC that have similar general features but very different details -- so I'm going to use nuclear import of proteins as an example of how biomolecules get through the pore.

Proteins that are translated in the cytoplasm, but destined for the nucleus (the proteins required to replicate DNA are a great example) tend to contain a short stretch of amino acids called a nuclear localization signal. While a molecule of this protein is being translated (the "cargo"), the NLS is recognized by a type of protein called an importin, which marks the protein to be translocated as cargo. Once translation is complete, the bound importin molecule interacts with the NPC and allows the cargo protein to diffuse through the NPC.

After the cargo protein enters the nucleus, the importin is removed by a nucleus-specific protein (a Ran-GTPase), which ensures that the transported protein remains in the nucleus.

Nuclear transport allows the roles of the nucleus and cytoplasm to be specialized, and is essential for the intricate molecular biology that eukaryotes rely on.