The Amino Acid Skeleton: Alpha Carbon and Side Chain

Module 2 · Lesson 1 of 3 · 4 min read · Beginner

All 20 standard amino acids that make up proteins share the same basic skeleton. Once you know it, you can read any of them.

At the centre sits one carbon atom called the alpha carbon. Four different things are attached to it. The first is an amino group, a nitrogen atom with hydrogens attached. The second is a carboxyl group, a carbon bonded to two oxygens. The third is a single hydrogen atom.

The fourth attachment is the side chain, often written as R. This is the only part that changes from one amino acid to the next. In glycine it is just a hydrogen atom. In tryptophan it is a large double ring. Everything that makes one amino acid different from another comes from its side chain.

The amino group and the carboxyl group matter because they are the parts that link up. The carboxyl group of one amino acid joins the amino group of the next to form a peptide bond. Repeat this many times and you get a backbone of alternating nitrogen, alpha carbon and carbonyl carbon atoms. The side chains stick out from this backbone like charms on a bracelet.

This design is powerful. The backbone is the same in every peptide, so cells can build chains with one set of machinery. The side chains supply the variety, which lets different sequences fold into different shapes.

References

1. Berg JM, Tymoczko JL, Stryer L. Biochemistry, 5th ed., Section 3.1: Proteins Are Built from a Repertoire of 20 Amino Acids (2002)
2. Alberts B et al. Molecular Biology of the Cell, 4th ed., The Chemical Components of a Cell (2002)

Educational content about laboratory research. Not medical advice. All Orion compounds are for laboratory research use only.