A New Way to Look at Protein

Proteins are extremely important because they constitute the majority of the structural tissue in your body, such as bone and the connective tissues that provide the shape and form to which your cells attach. The eminent importance of protein to our life is reflected in the term itself: protein is derived from the Greek term protos, which means "taking first place." Proteins are involved in just about every function in your body, in particular, enzymes are proteins, and enzymes are the molecules in the body that do much of the work like building new tissue, breaking down old tissue, and even providing channels in your cells' membranes to let in necessary nutrients, plus removing wastes and toxins from the body by metabolizing, or breaking them down.

Your body is constantly making new proteins to replenish those lost from tissue damage, to fight invaders and protect your body, and to provide for growth. For example, the antibodies of your immune system, some hormones of your endocrine system, the enzymes in your digestive system, and the blood coagulating factors of your circulatory system are all made of proteins.

Amino Acids

Proteins are made up of smaller molecules called amino acids that are strung together by chemical bonds like beads on a chain. To become an active, functional protein, this string of amino acids folds in on itself forming a twisted and entwined, three-dimensional structure. Proteins come in many sizes. Some chains of amino acids are quite small, for example, the hormone insulin, a protein which is only 51 amino acids long. Most proteins, however, are larger. Most of proteins in your body contain between 200-400 amino acids, for example, many of the enzymes your body uses for digestion of food such as chymotrypsin, which is 245 amino acids, or pepsinogen, which is 362 amino acids. Some of the proteins in your body are very large. The protein hemoglobin, which carries oxygen in your blood to your cells, is made of 574 amino acids; the immunoglobulins that help protect your body from infectious invaders contain 1,320 amino acids, and the ATPase complex, the enzyme at the end of the electron transport chain in the mitochondria (the energy-production factories in our cells), is composed of 9 large protein chains containing around 3,000 amino acids in total.

Individual proteins also can join together to form large protein complexes. The largest protein complexes in your body are the proteins that make up the matrix of your bone, skin, nails, hair, tissue and teeth upon which all your cells attach. These include proteins like collagen, elastin (which gives your skin its elasticity), and keratin. Collagen, for example, is composed of three strings of 1,000 amino acids each that twist together into a long, cylindrical chain of 3000 amino acids. This chain then complexes with many other collagen chains to form a thicker, stronger cylinder, called a fibril. Fibrils can have 6 to 20 or more collagen chains per section, which means they can contain tens of thousands of amino acids in one protein structure. Fibrils provide the structure upon which your bone mineralizes, and they crisscross throughout your soft tissue to keep your cells in contact with each other.

The single amino acid is similar to a simple sugar, in that it is the single unit your body works with to build larger protein chains. And, in a manner similar to the digestion of carbohydrates, your body breaks proteins down to amino acids during the digestion process, taking in only the small single amino acid unit, or sometimes a two or three amino acid unit. Like carbohydrates, amino acids are composed of carbon, hydrogen, and oxygen, but unlike carbohydrates, amino acids also contain nitrogen. In fact, amino acids are your body's way of getting this necessary component: nitrogen.

How Much Protein Do I Need and How Do I Get It?

A healthy adult is estimated to need around 40 to 65 grams of amino acids per day. If this is not provided in the food you eat, your body will begin to break down its own muscle to support its need for amino acids. Inadequate intake of amino acids from protein can lead to stunting, poor muscle formation, thin and fragile hair, skin lesions, a poorly funcitoning immune system, and many other symptoms. You get these amino acids primarily from the protein in plant and animal foods, which requires digestion. Free amino acids, which require no digestion, just absorption in the small intestines, are also present in whole foods, but are often removed during processing. Although vegetables and grains do provide some proteins, you get the majority of your protein from nuts, legumes, eggs, fish, meats and dairy products.

In processed foods, protein is sometimes provided as hydrolyzed proteins, which means it has been chemically cut into smaller chains of from two to 200 amino acids, which are called peptides. Some specially produced foods for hospital or healthcare use are made of elemental amino acids; these products provide the free amino acids themselves and require no digestion before absorption.

Peptides are short strings of amino acids bonded together. Since there are twenty different amino acids, a great number of different peptides can be created. When peptides link together, they undergo chemical processes that cause their molecules to fold in upon themselves, creating a complex structure classified as a protein.

The Essential Amino Acids: What Are They and Why Do I Need Them?

Amino acids are made into approximately 20 different versions, and proteins require all of these at some level, so for your body to make a protein, it must have all 20 amino acids available. Your body can synthesize many of these amino acids from other molecules; however, nine amino acids cannot be made in your body. These are called the "essential" amino acids, because your diet must supply them for your survival. Examples of essential amino acids include leucine, methionine, phenylalanine, and tryptophan.

All proteins have these essential amino acids, but your body requires them in certain amounts and ratios to each other. Animal foods contain these amino acids in ratios that are similar to those found in humans, while most plant-based foods do not. In the past, people were concerned that vegetarians and people whose diets consisted mostly of plant foods were at risk of protein deficiency since they were not eating "complete" proteins. More recently, this old theory has been rejected. Researchers and healthcare practitioners have suggested that since different plant-based foods provide different essential amino acids, eating a varied diet featuring whole grains, legumes, and vegetables does provide all of these important building blocks to sustain health and promote vitality. In addition, some plant-based foods, such as soy, actually feature an essential amino acid protein profile similar to animal-based foods.

This page was updated on: 2003-11-15 01:02:50
© 2002 The George Mateljan Foundation