Amino Acids vs. Proteins
Difference Between Amino Acids And Proteins
Proteins constitute the third major class of biological building blocks. Proteins are the structural material of muscles and help form other organs as well as hair and nails. In the form of enzymes, certain proteins direct the moment-to-moment chemical activities of every cell, organ, and living system. Still other proteins form part or all of the many hormones that carry messages between living cells. Hair and silk are examples of natural products made primarily of protein.
Proteins differ from carbohydrates and lipids in that their molecules always contain nitrogen and often contain sulfur atoms. Proteins make up some of the largest and most complicated molecules found in living organisms. In essence, they are long chains of hundreds to thousands of smaller units called amino acids. The specific order of the amino acids determines each protein’s special properties.
As its name suggests, an amino acid is made up of an organic acid with an attached amino group, -NH2. The proteins found in living things are made up primarily of an assortment of 20 common amino acids. The simplest is glycine (NH2CH2COOH). The individual amino acids are linked together through bonds between the carbon end of one amino acid and the nitrogen end of the next. This special type of bond is called a peptide linkage.
The human body can manufacture many of the amino acids it needs. But we have to obtain nine from the food we eat. These nine are known as essential amino acids. Certain foods—such as meat, dairy products, soybeans, and eggs—contain a complete set of all the essential amino acids. They are often called complete proteins. Incomplete proteins include foods such as most grains and beans, which must be combined to create complete proteins. Combining two incomplete proteins, such as beans and rice, creates a complete protein. They must be combined for complete nutrition. Diets that lack some or all of the essential amino acids can lead to protein-deficiency disease, or kwashiorkor, still common among young children in impoverished regions of the world.
When the body digests food proteins, it uses various enzymes to break them down into their constituent amino acids. The body then reassembles these amino acids into the specific proteins it needs. Even the simplest protein in the human body contains no less than 30 amino acids. The most complicated contain thousands.
The linear sequence of amino acids in a protein’s stretched-out chain is the protein’s primary structure. Attractive forces between the amino acids in the protein chain cause this primary structure to twist, coil, and fold in on itself in various places. The resulting spirals, helices, and sheets are the protein’s secondary structures. Most proteins have several different kinds of secondary structures. Taken together, they determine the protein’s overall three-dimensional shape, or tertiary structure.
This complex twisting and folding holds a protein in the highly specific configuration needed to act as a catalyst for one or more chemical reactions. Unfolding, or denaturing, a protein destroys this function, though the amino acids may remain linked together in their proper order. You see the effects of denaturation whenever you cook an egg. Heat denatures the egg white’s albumin protein—turning it in the process from a clear liquid to a white solid.