A tour of the cell
A tour of the cell

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

Nuclear structure and the transport of molecules

The structure of the nucleus is maintained by a family of intermediate filament proteins known as lamins, which form a network of filaments on the inner surface of the nuclear membrane. This network is called the nuclear lamina and is linked both to the nuclear membrane and to the chromatin; the nuclear lamina is thought to help to organise the chromatin.

When viewed at high magnification, it can be seen that the membrane that surrounds the nucleus is actually a double membrane, or nuclear envelope, as it is sometimes called. Within the envelope are gaps called nuclear pores (Figure 11b and Figure 14) which create channels of about 9 nm diameter. Small water-soluble molecules diffuse freely through the nuclear pores, but the movement of proteins into and out of the nuclear pore is regulated by a complex arrangement of proteins known as the nuclear pore complex. The nuclear pore complex allows RNA molecules and ribosomes to pass out of the nucleus, and allows selected proteins to enter the nucleus, but prevents passage of most other proteins.

  • What type of proteins would you predict to be transported into the nucleus from the cytoplasm?

  • Histones, which are needed for the packing of DNA; the enzymes and other proteins needed for replication and transcription of DNA; the proteins needed for ribosome assembly; and the proteins that make up the nuclear lamina.

Described image
Figure 14 TEM micrograph showing the surface of the nuclear envelope and the nuclear pores.

The nucleus, then, is crucial as the site of DNA replication, transcription of DNA into RNA and ribosome assembly. You have seen that the ribosome subunits and mRNA molecules leave the nucleus through the nuclear pores. The next section describes what happens to them in the cytosol.

Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to University-level study, we offer two introductory routes to our qualifications. You could either choose to start with an Access module, or a module which allows you to count your previous learning towards an Open University qualification. Read our guide on Where to take your learning next for more information.

Not ready for formal University study? Then browse over 1000 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus371