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.

Free course


1 The three-dimensional nature of proteins

1.1 Introduction

Proteins are made up of one or more polypeptide chains, polymers of amino acid residues found in all proteins. The structure that a polypeptide adopts is determined by the component amino acid units – both their chemical properties and the order in which they occur in the polymer – and by the structure of the peptide bond that links them.

Protein structure is described in terms of four levels of organisation: primary, secondary, tertiary and quaternary. The linear sequence of amino acids in the polymer is its primary structure and the conformations that the polypeptide adopts are described as secondary structure. The arrangement of elements of secondary structure in a folded polypeptide defines its tertiary structure, and, finally, the quaternary structure describes the association of two or more folded polypeptides in multisubunit proteins. In this section, we will begin by considering the structure of the peptide bond, and then go on to look at each of the levels of protein structure in turn.


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