Nutrition Science and Everyday Application - beta v 0.1

Protein Structure
WHAT IS PROTEIN?
Proteins are macromolecules composed of amino acids. For this reason, amino acids are
commonly called the building blocks of protein. There are 20 different amino acids, and we
require all of them to make the many different proteins found throughout the body. Proteins
are crucial for the nourishment, renewal, and continuance of life.
Just like carbohydrates and fats, proteins contain the elements carbon, hydrogen, and
oxygen, but proteins are the only macronutrient that also contain nitrogen as part
of their core structure. In each amino acid, the elements are arranged into a specific
conformation, consisting of a central carbon bound to the following four components:
• A hydrogen
• A nitrogen-containing amino group
• A carboxylic acid group (hence the name “amino acid”)
• A side chain
The first three of those components are the same for all amino acids. The side
chain—represented by an “R” in the diagram below—is what makes each amino acid unique.
Figure 6.1. Amino Acid Structure.
Amino acid side chains vary tremendously in their size and can be as simple as one
hydrogen (as in glycine, shown in Figure 6.1) or as complex as multiple carbon rings (as
in tryptophan). They also differ in their chemical properties, thus impacting the way amino
acids act in their environment and with other molecules. Because of their side chains,
some amino acids are polar, making them hydrophilic and water-soluble, whereas others
are nonpolar, making them hydrophobic or water-repelling. Some amino acids carry a
negative charge and are acidic, while others carry a positive charge and are basic. Some
carry no charge. Some examples are given below. For this class, you don’t need to memorize
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