Intracellular transport
Intracellular transport

This free course is available to start right now. Review the full course description and key learning outcomes and create an account and enrol if you want a free statement of participation.

Free course

Intracellular transport

4 Signals for compartmentalisation

4.1 Introduction

We have noted how proteins for different destinations are packaged in transport vesicles, a process that depends on signal sequences in the proteins. In this section we shall look in a little more detail at the nature of the signal sequences. Except for the few proteins synthesised in the mitochondria or chloroplasts, cellular proteins are encoded by nuclear genes and synthesised on ribosomes in the cytosol or at the ER. Consequently, these proteins, if destined for organelles, must be sorted to the correct target membrane and translocated to the organelle. Sorting of proteins for their ultimate destinations occurs in conjunction with a variety of post-translational modifications. These modifications represent ‘recognition signatures’ for a variety of biological processes, including organelle targeting, subcellular anchoring and the formation of macromolecular complexes.

  • In the absence of a signal sequence, or if the signal sequence is removed by genetic modification, where is the protein likely to end up?

  • At the plasma membrane. Constitutive secretion is the default pathway (Section 2.4) and specific signals are needed to retain proteins in the ER and the Golgi or to direct them to the secretory pathways or lysosomes.


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, find out more about the types of qualifications we offer, including our entry level Access courses and Certificates.

Not ready for University study then browse over 900 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 prospectus