1.5.3 Amino acid sequences
With 20 different amino acids as constituents and proteins several hundred amino acids long, it would in theory be possible to construct an almost infinite number of different protein molecules. But a particular protein only functions correctly in the body if it is made of a particular set of amino acids joined together in precisely the correct sequence.
In what form does the code exist that enables cells to make proteins and all their other components?
The code exists in the DNA, which is present in chromosomes in the nuclei of human cells. This code gives the sequence of amino acids needed to make each protein.
The first protein whose amino acid sequence was worked out in the laboratory was insulin, a hormone secreted by the pancreas. Although insulin is composed of only 51 amino acids (as you will see later in Figure 8), it nevertheless took almost six years for a group of research scientists in Cambridge to complete the task. The group was headed by Frederick Sanger, who was awarded the Nobel Prize for this work in 1958. Since then, the speed of finding out the sequence of amino acids in a protein (a process known as ‘sequencing’) has increased hugely and the time for the process can now be measured in hours, rather than years.