Proline: Structure & Overview

Instructor: Brekke Peterson Munks
Proline is one of 20 amino acids that play a vital part in biological life. In this lesson, you'll learn how proline is structured, why it's important and where you can find it. Then, test your knowledge with a quiz.

The Structure of Proline

Amino acids are the building blocks of proteins and, as such, are one of the largest components of cells, tissues and muscles in humans. They have a variety of other roles as well, from helping control insulin and repairing muscle tissue to aiding in metabolism and absorption of vitamins and minerals.

Denoted by the abbreviations of P or Pro in scientific literature, proline is distinct in structure compared to other amino acids because its amino group is cyclical. The basic formation of an amino acid includes an amino group (made up of one nitrogen atom and two hydrogen atoms), a central carbon atom, a carboxyl group (a carbon atom double bonded to one oxygen atom and singly bonded to another oxygen atom that's bonded with a hydrogen atom) and a side chain referred to as an R-group.

Basic amino acid structure
Basic amino acid structure

The amino group, central carbon atom and carboxyl group make up the backbone of all amino acids, with the side chain always branching off the central carbon. Well, almost always.

In proline, the R-group is bonded to the central carbon as well as the nitrogen atom of the amino group, forming a house-like structure, as seen below. This makes proline unique in structure among all other amino acids.

Structure of proline

Function of Proline

The nitrogen in proline isn't bound to hydrogen when in a protein or peptide bond. Additionally, proline is very rigid in structure. As a result, this amino acid can't donate hydrogen to stabilize other bonds or promote stability of molecules.

However, even without hydrogen donation, proline can promote stability in secondary protein structures, which are 3D forms of local segments of proteins. Proline is generally found at the beginning of a protein or on the sides of structures that turn, called helices. This is because proline isn't linear and can cause the protein to twist or have an angled shape.

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