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Protein in the DietSo, where do the amino acids come from that are used to synthesize protein? Plants make their own. They start with glucose from photosynthesis and take nitrogen from nitrates and ammonia in the soil and through a variety of chemical reactions synthesize the amino acids which in turn can be used to synthesize the proteins. What about humans and other animals? Our bodies can make some of the amino acids that we need but essentially we get most of them from the proteins in our diet. We ingest those proteins from a variety of sources, whether they are plant or animal, and then those proteins are hydrolyzed (broken down) into the amino acids from which they were made. These are then absorbed and transported to the cells where they are converted back into protein in the process that we talked about earlier in this lesson. We will also be talking about that process some more in the next lesson on nucleic acids. In many ways it doesn't really matter what protein we eat, because the protein that we need to use in our bodies is created from the amino acids. What is important is that the protein we ingest, whether from animals or plants, contains the amino acids that we will need to make the protein that we use and it needs to have those amino acids in the proportion in which they are needed to make our protein. The term that is used to describe protein that contains all of the amino acids that are needed in roughly the proportions that they are needed is complete protein. One of the advantages of animal protein over vegetable protein as a dietary source of protein is that animals contain the same kinds of protein that we are going to make out of the amino acids that are contained in that protein; therefore, protein from meat is complete protein. Plant protein is just as good a source for amino acids as animal protein as long as it contains the same kinds of amino acids. Usually this requires a bit of mixing - some variety in the diet that will include different sources of plant protein which will, in combination, have the right mix of amino acids. One tradition way of achieving complete protein from plant sources is to combine beans and rice in the same meal. Another term that comes up when we talk about protein nutrition is the term essential amino acid. Our bodies can make quite a number of amino acids from other chemicals that are contained in the body and can convert some amino acids into other amino acids. However, there are some amino acids we are not able to synthesize ourselves. Those particular amino acids and they must be provided to us in our diet. Those amino acids are referred to as the essential amino acids. It's not to say that the non-essential amino acids are not necessary, it's just that it is not necessary for them to be in our diet because other things in the diet can be used to make them.
E-mail instructor: Sue Eggling Clackamas Community College |
