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The Chemistry of Food, Part 3--Proteins and Amino Acids

© Linda Mamassian

Proteins are an important class of macronutrients (along with carbohydrates and fats). Our bodies use proteins for growth and to build and repair body tissues. Hormones, antibodies, and the enzymes that regulate the body's chemical reactions are all made of protein. Each protein is a large complex molecule made up of a long chain of building blocks called amino acids. The molecular weights of protein molecules range from about 10,000 to over 1,000,000 amu (atomic mass units).

When you eat protein in food, digestive enzymes break the protein down into shorter amino acid chains (polypeptides and then peptides) and finally into individual amino acids. The amino acids then enter the blood stream and travel to the cells where they are incorporated into new proteins.

The 20 amino acids the body needs can be linked in thousands of different ways to form thousands of different proteins, each with a unique function in the body. Humans can make some of the amino acids within their own bodies, but eight must be eaten in our food and are called essential amino acids. (Two others, histidine and arginine, are essential for infants.) The names, structural formulas, and 3-D models of the amino acids are shown in the table below.
 

Amino Acids

Name (Essential/Nonessential)	Chemical Structure	3-D Model
Alanine Nonessential
Arginine Essential for infants
Asparagine Nonessential
Aspartic Acid Nonessential
Cysteine Nonessential
Glutamic Acid Nonessential
Glutamine Nonessential
Glycine Nonessential
Histidine Essential for infants
Isoleucine Essential
Leucine Essential
Lysine Essential
Methionine Essential
Phenylalanine Essential
Proline Nonessential
Serine Nonessential
Threonine Essential
Tryptophan Essential
Tyrosine Nonessential
Valine Essential

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