Christina Woodard, age 14, of Salt Lake City, Utah, for her question:
What exactly are proteins?
Proteins are the vital chemicals that every living cell needs to keep going. No wonder they are given such high priority in our daily diets. Actually, they are groups of simple molecules arranged in very complex chemical units. The simple units are made mostly from carbon and hydrogen, oxygen and nitrogen perhaps with other common elements such as iodine or sulphur.
The small units from which proteins are constructed are called amino acids. Bio¬chemists have found more than 60 different amino acids in various plant and animal cells. However, it seems that only about 20 of these are used to build the complex chemical units classed as proteins. Plants use the energy of sunlight to build simple raw materials into the proteins from certain foods they eat.
A protein molecule is a long chain of perhaps hundreds of units selected from 20 or so amino acids. The number of possible combinations is astronomical. And each living cell has a built in chemical lab to assemble the precise proteins it needs to perform this or that function.
We are told that meat and fish, milk and cheese and various vegetables are rich in proteins. So they are.' But as items in our daily diet, let's think of them as protein building foods. For our bodies are unable to use these ready made proteins as served. They must be properly digested to break them apart into amino acid units. Then the basic units are reassembled to form the particular proteins needed by the body.
Various amino acids are found distributed among the cells. There, in each nucleus, the DNA waits with its genetic blueprint of instructions. Prompted by subtle signals, it issues coded orders to assemble the available amino acids in certain protein struc¬tures. The assembly line is managed by RNA, the messenger biochemical. As this mir¬aculous chemistry proceeds, specially structured proteins are built and sent to fulfill this or that function in the fantastically complex business of cellular metabolism.
Proteins of various types make up the bulk of plant and animal tissues. Meaty muscles and plant fibers, nails and claws, hair and horns are made mostly of building type proteins. Other protein types perform more subtle duties as enzymes that govern vital cellular activities and hormones that signal general alerts to coordinate the reactions of the entire body.
The human body needs 20 or so different amino acids to build the many types of protein it needs. The variety of foods on a balanced daily diet should include these 20 units in digestible forms. No one food contains them all in balanced amounts. This is the main reason why nutritionists list a wide variety of foods on the diet. The other reason is that a varied menu tempts the taste buds and this pleasant ex¬perience helps the process of digestion.