Nutrition: Proteins
Nutrition: Proteins

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

Nutrition: Proteins

1.6.3 A faulty shape

An example of the effect of a single change in the amino acid sequence of a protein is provided by haemoglobin, the protein in the red blood cells that binds oxygen as it is transported from the lungs to the cells elsewhere in the body. The sixth amino acid in the haemoglobin chain starting from the amino end, is normally glutamate, but in some individuals, valine appears there instead, profoundly altering the shape of the haemoglobin molecule.

Activity 29

The R groups of glutamate and valine are shown below.

Why do you think the shape of the haemoglobin molecule is affected so much when valine replaces glutamate?

Discussion

The R group of glutamate carries a negative charge (—COO, carboxylate group), which interacts with other charged groups and is important in determining the overall shape of the haemoglobin molecule. The R group of valine has no charge and so is unable to take part in such interactions.

Haemoglobin molecules with valine at position 6 fold up into the wrong shape. The red blood cells containing this type of haemoglobin assume a curved ‘sickle’ shape under certain conditions, as shown in Figure 9a, instead of the normal disc shape (see Figure 3). This altered shape is distinctive of the condition known as ‘sickle cell disease’. The characteristics of the disease are shown in Figure 9b. This case is just one example of how the correct amino acid sequence of a protein is fundamental to the way that the protein functions.

Figure 9
Figure 9 Sickle cell disease. (a) Red blood cells of a person with sickle cell disease, at various stages of sickling. (b) Origin and characteristics of sickle cell disease
SK183_1

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 over 40 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