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Download All About Proteins Proteins are highly folded polymers constructed
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All About Proteins Proteins are highly folded polymers constructed from monomers called amino acids. There are 20 Amino Acids and ALL have the same structure except for the R group or side chain. Notice the variety in the R groups shown below – and no, you do NOT need to memorize them. You DO need to recognize and be able to draw the general structure of an amino acid shown at left. The R groups are important because they may make an amino acid nonpolar, or polar, and some of the polar ones may become charged in water or act as acids or bases. These properties will play a role in helping the finished protein form. Amino acids by themselves are of no use to organisms. Instead, they must be formed into proteins. This process involves several stages. First, a polypeptide must be formed. We pretty much know how to do this – dehydration synthesis! Just as the process of building a triglyceride from glycerol and fatty acids looked a bit different from what you learned about joining monosaccharides, peptide bonding uses still different groups to provide the hydrogens and oxygen. However, once the bond is formed, a molecule of water will be made as a byproduct. How many peptide bonds are needed to link together 3 amino acids? How is the linking together of amino acids different from linking together carbs and lipids parts? Notice that the amino acids will always be lined up in the same way when creating a polypeptide. The amino group will always be left intact on the first amino acid in the chain, and the carboxyl group will be left on the last amino acid. This lets us define which amino acid is first in line and which is the last, as well as the position of every amino acid in between. This can be absolutely critical for making a complete and functional protein. How do we go from a polypeptide to a protein? The short answer is… very carefully! Lots of twisting and folding is required and a complex set of rules guides all this action. A finished protein can be described in terms of its level of structure. Four Levels of protein structure Basically, what you need to know for this class is the following: 1) The order of amino acids (primary structure) determines EVERYTHING ELSE!!!!! It is the unique characteristics of the individual amino acids that causes the chain to start folding up in a specific shape. 2) If you change the order of amino acids, you can change the structure of the final protein. This can mean the difference between curly hair or straight hair. 3) A proteins shape determines it function. If made incorrectly, it can result in terrible consequences for the organisms. This is basis for genetic diseases we will talk about this year. 4) We “know” how to put together the right amino acids to build a specific protein because the information is coded in our DNA! Essential vs. Non-essential Amino Acids Humans can produce 10 of the 20 amino acids. The others must be supplied in the food. Failure to obtain enough of even 1 of the 10 essential amino acids, those that we cannot make, results in degradation of the body's proteins—muscle and so forth—to obtain the one amino acid that is needed. Unlike fat and starch, the human body does not store excess amino acids for later use— the amino acids must be in the food every day. ?The essential amino acids are arginine (required for the young, but not for adults), histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. These amino acids are required in the diet. Plants, of course, must be able to make all the amino acids. Humans, on the other hand, do not have all the enzymes required for the biosynthesis of all of the amino acids. Since the foods we eat contain complete proteins and not just amino acids, what process occurs during digestion to free the individual amino acids? Why might it be important for someone who is training heavily for an athletic season to eat large amount of protein in their diet? Functions of Proteins Making a complete protein properly is obviously a complex process, and it provides virtually no limit to the shapes that can be formed. That is why we will not ask you to memorize a standard form for a complete protein – there isn’t one! Given all the complexity that is possible, you might guess that proteins can do many different jobs and you would be correct. A few important functions of proteins are as follows. Look up on the internet what each of these means in terms of a biological context. Enzymes: Structural proteins (collagen, cartialage): Contractile proteins (actin/myosin): Chemical messengers (hormones): Receptors: Membrane transport proteins: Defense (Antibodies):