|MadSci Network: General Biology|
Aloha,Savanna, Protein is essential for humans...that means that we can't do without it in our food and in our bodies, in part because of the nitrogen it contains (the major source of nitrogen for the body) and in part because of the particular building blocks that make up protein. Protein is made up of twenty different building blocks, called amino acids, arranged in thousands and thousands of different ways. Every cell in the human body contains protein as part of its structure (cell membrane and other structures). It also serves to build strong stuctures in the body, as a whole (bones, muscles, tendons, and ligaments); it makes up the compounds that your body used to make the biochemical reactions occur in your body, called enzymes; it is found in your blood as parts of the red blood cells (hemoglobin) and as carriers for other materials (transport proteins); and it is part of the immune system (antibodies) that helps protect your body from foreign invaders, such as bacteria, viruses, and toxic substances. Some proteins help keep the fluid in your body where it should be, such as the proteins in your blood. Some proteins in your blood and other tissues help keep the acid-base balance in your body in ranges that allow you to stay alive. This last function is kind of interesting. The structure of proteins allows them to act as either acid or base...and they can break apart in the body to help neutralize too much base or acid, especially in the blood stream. There are some hormones that are built up of proteins; hormones are very complicated compounds made in one organ and then moved somewhere else in the body to have their effect. For example, insulin, a hormone made in the pancreas and important for keeping the glucose level in your blood stream at a safe and healthful level, is actually a protein. It helps take glucose in the blood stream into tissues where it can be used as energy or be stored away for future use. Lastly, speaking about energy, your body can use the proteins in your food (from both plant- and animal-based foods) for energy...you get about 4 kilocalories/gram from protein. However, your body 'prefers' to use a mixture of carbohydrate and fat for energy...not a lot of protein. Under certain circumstances (starvation, a reducing diet, illness), your body will use protein for energy, when the supply of the other two nutrients gets low or is not available. This limitation on the use of protein is because protein (and the amino acids that make up protein) are better used for the other purposes that I have mentioned above. As I reread what I have written, it sounds very much like part of the lecture that I do on 'protein' for my introductory nutrition students, here at the University of Hawai`i/Manoa. In fact just to make sure that I didn't forget anything, I used the textbook (Contemporary Nutrition, Wardlaw, 5th edition)to help me with the answer. To recap, protein is needed in the human body for 6-7 main reasons: part of body structures (from cell to organ to system), maintain fluid and acid-base balance, makes up some hormones and all enzymes, important for the immune system, and a sometime source of energy. One last comment, from the nutrition scientist in me. We, in the US, probably get plenty of protein in our food. In fact, most of us eat about 2-3 times what our body actually needs. The body just breaks apart the extra protein and stores away the byproducts or uses them for energy. Most of our protein in the US comes from animal food (meat, poultry, fish, and animal products, like eggs and milk). The rest comes from plants (grains, seeds, and some vegetables). Some nutritionists, myself included, think that the proportions of where our protein comes from should be reversed, for a number of reasons (health, economics, environment)...that is, we should get less of our protein from animal foods and more from plant foods. Can you think of some reasons why I might say this? Good luck on your project...I judge for the Hawai`i State Science Fair every year!
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