Where does the name "protein" come from?
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The name protein is derived from the Greek term proteos, which means “primary” or “to take place first”. Protein was first identified in a laboratory about a century ago at which time scientists described it as a nitrogen-containing part of food that is essential to human life. While protein has long been the darling of the weight lifting and sport community, over the past few years there has been more attention focused on the importance of protein during weight loss and general health. |
What are amino acids?
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We now know that all proteins are collections of amino acids. Said another way, amino acids are the “building blocks” of proteins. Although the final functional form of some proteins may contain minerals or other nonprotein components, the basis for these proteins is still amino acids. All amino acids have the same basic design, as shown in Amino Acid Figure. There is both a nitrogen-containing amino portion and carboxylic acid portion attached to a central carbon atom. The presence of both an amino and an acid portion on each molecule led to the name amino acid for this family of molecules. There is also a hydrogen atom attached to the central carbon, as well as a mysterious “R” group. |
An amino acid contains a central carbon atom (C) with the following attachments:
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Amino group
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Carboxyl (carboxylic acid) group
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Hydrogen (H)
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“R” group or side chain
The R group denotes the portion of an amino acid that will be different from one amino acid to the next. The R portion of an amino acid may be as simple as a hydrogen atom, as in glycine, or much more complex to include carbon chains and rings, acid or base groups, and even sulfur (S). The structure of the twenty amino acids used to make protein is shown in Amino Acids Figure.
How many amino acids are in proteins?
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There are probably hundreds of different amino acids found in nature, but only twenty are incorporated into the proteins found in living things (see Amino Acid Table). This means that these twenty amino acids are the basis of protein found in birds, lizards, plants, bacteria, fungi, yeast, and so on. This is a very profound and also convenient situation. First, it allows us to further appreciate that, despite the obvious structural and functional differences between the different life-forms on this planet, there is common ground and more than likely common ancestry. |
Second, it somewhat simplifies human nutrition as we are able to obtain all of the amino acids we need to make our body proteins by eating the proteins of other life-forms on this planet, there is common ground and more than likely common ancestry. Second, it somewhat simplifies human nutrition as we are able to obtain all of the amino acids we need to make our body proteins by eating the proteins of other life-forms .
Some proteins contain just a few amino acids linked together, while others contain hundreds of amino acids. Scientists often refer to the links of amino acids in the following manner:
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Peptides are two to ten amino acids including dipeptides, tripeptides, etc.
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Polypeptides are 11 to 100 amino acids.
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Proteins are > 100 amino acids.
Other scientists will describe protein size based upon the weight of the protein molecule (molecular weight) and sometimes use the term Daltons as a unit of weight. When we discuss proteins in this book we will only refer to protein size and design only if its helps us understand a protein’s unique function.
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