Amino Acids - Protein Synthesis
The topic of amino acids and protein synthesis is complex, but can be broken down into a series of smaller arguments in the same way that sugar chemistry in the body can be reduced to a more simple explanation. An amino acid has two features: a carboxylic acid (CO2H) and an amine (NH2). The amino (amine) part may be further substituted and the amino part of one amino acid can link to the acid function of another, a water molecule then being lost: a peptide bond is formed. There now exists a new chemical entity comprising two amino acid units. A third amino acid can combine with the new compound forming yet another different one but involving three amino acid units. This extension by peptide bond formation continues several hundred times creating a long chain of amino acid units but simply linked through the amine part of one and the carboxyl group of another. The linking can be linear, branched or a mix of both. The number of amino acids known runs into thousands but those involved in the formation of human protein numbers only 20 and of these 8 are so called essential in that the body has no mechanism to synthesise them and another set of 8 are considered conditionally essential and the two requirements can be differentiated.
Essential (8):
Conditionally Essential (8):
Non-Essential (4):
Relatively simple chemistry is involved in the formation of the non-essential amino acids, but tyrosine can be synthesised from phenylalanine and is an example of an essential amino acid being used to make another essential amino acid [conditionally essential] and if any amino acid is lacking in the diet, protein will be destroyed by catabolism (breaking up into its constituent amino acid parts) and the deficient amino acid used from this source. Protein loss is then greater than that of synthesis. Amino acids are used not only to form the two proteins used in muscle growth (actin and myosin) but also the many thousands of other structural proteins in the human body for tissue repair.
Animal and vegetable are the two main sources of dietary protein and each has many of the necessary amino acids, but protein from vegetable sources has in some cases less of the essential amino acids. This does not mean that the quality of non-animal protein should be underestimated. A combination of two or more types of non-animal protein may complement one another by providing sufficient amounts of all. For example, cereals are generally high in methionine and tryptophan but low in lysine. Pulses on the other hand are low in methionine and tryptophan but have a high lysine content. Between them all three amino acids are available in quantity as in the combination of beans on toast.
In much the same way that the 26 letters of the alphabet can be arranged to make many thousands of words the 20 amino acids can produce the 200,000 proteins found in the human body. It is the particular sequence of amino acids in the polypeptide chain which distinguishes one protein from another. The resulting shape of the large molecule in its twists and turns creates a definite form. In water, the most abundant liquid in the body, there exist what are known as hydrogen bonds. These are electronic features which bind portions of the same molecule (intermolecular) together so producing this definite shape. Different molecules can also be bound together to form a regular shape (intramolecular defines between different molecules). The contractile protein actin is one instance where two string like strands are twisted together reinforcing the structure of the protein. Imagine two lengths of rope twisted together. The resulting strength of the two strands linked together is far greater than each one separately. The outside of the protein actin has a hydrophilic (attracted to water) and internally a hydrophobic (repels water) part but which is attracted to other hydrophobic portions of the molecule. So, internally there is binding between the two strands and externally stability in water.
Protein synthesis occurs in the cell. The code to copy the exact sequence of construction of a protein is retained within the cell structure. The mechanism by which this is done is very complex and involves messenger RNA (mRNA), transfer RNA (tRNA) and ribosomes but the result is the definite order of amino acids to produce a particular protein maybe many hundreds or thousands of amino acid units in length. There is nothing random about the synthesis of protein.
An interesting question arises concerning the formation of the actin/myosin, the contractile proteins of muscle. Most proteins are structural in some way and are synthesised by the body to repair and replace damaged tissue, but what causes a large amount of these two proteins to be made in the muscle growth process? Is it to repair damaged muscle that has been stressed that causes this growth? Or some other response mechanism triggered within the body when muscle has been stressed? Clearly though, muscle must be considerably stressed to result in growth. Does (physical not psychological) stress trigger the release of human growth hormone (somatotropin)?
It is important to appreciate that protein synthesis (anabolism) and degradation (catabolism) is taking place constantly. This is generally known as metabolism, but involves both synthesis and degradation. Once a protein has been constructed it will not exist in that form forever. New and identical protein will replace older protein which is broken down into the constituent amino acids and these acids reused to form new and different protein. The amino acid pool. This process ensures that newly ingested protein through diet and amino acids already in the body are always available to synthesise any protein necessary for the survival of the life form. All protein-containing body tissue is constantly being regenerated. Over a variable period, every cell-type has died off and been replaced by a new one. The single cell is a complete entity capable of replication (reproducing itself). The human body is a mass of countless billions of different cells which coexist as the human and the particular collection of cells distinguishes the human from any other animal species. Cells die off but are replaced with new ones. The dead material is eventually removed from the body.
In the normal mixed diet it is not likely that any particular amino acid will be deficient. In most sources of animal protein all the amino acids are present, but in differing amounts. It is difficult to estimate the actual levels without knowing the exact sequence of amino acids in any specific protein since thousands of different proteins are probably present in total. However, if 1.5g/kg protein were used as a guide then 120g of protein would be the daily intake for someone of 80kg body weight. Obviously, with increased body mass (of muscle) then the greater the level of protein that must be consumed.
Essential (8):
Conditionally Essential (8):
Non-Essential (4):
Relatively simple chemistry is involved in the formation of the non-essential amino acids, but tyrosine can be synthesised from phenylalanine and is an example of an essential amino acid being used to make another essential amino acid [conditionally essential] and if any amino acid is lacking in the diet, protein will be destroyed by catabolism (breaking up into its constituent amino acid parts) and the deficient amino acid used from this source. Protein loss is then greater than that of synthesis. Amino acids are used not only to form the two proteins used in muscle growth (actin and myosin) but also the many thousands of other structural proteins in the human body for tissue repair.
Animal and vegetable are the two main sources of dietary protein and each has many of the necessary amino acids, but protein from vegetable sources has in some cases less of the essential amino acids. This does not mean that the quality of non-animal protein should be underestimated. A combination of two or more types of non-animal protein may complement one another by providing sufficient amounts of all. For example, cereals are generally high in methionine and tryptophan but low in lysine. Pulses on the other hand are low in methionine and tryptophan but have a high lysine content. Between them all three amino acids are available in quantity as in the combination of beans on toast.
In much the same way that the 26 letters of the alphabet can be arranged to make many thousands of words the 20 amino acids can produce the 200,000 proteins found in the human body. It is the particular sequence of amino acids in the polypeptide chain which distinguishes one protein from another. The resulting shape of the large molecule in its twists and turns creates a definite form. In water, the most abundant liquid in the body, there exist what are known as hydrogen bonds. These are electronic features which bind portions of the same molecule (intermolecular) together so producing this definite shape. Different molecules can also be bound together to form a regular shape (intramolecular defines between different molecules). The contractile protein actin is one instance where two string like strands are twisted together reinforcing the structure of the protein. Imagine two lengths of rope twisted together. The resulting strength of the two strands linked together is far greater than each one separately. The outside of the protein actin has a hydrophilic (attracted to water) and internally a hydrophobic (repels water) part but which is attracted to other hydrophobic portions of the molecule. So, internally there is binding between the two strands and externally stability in water.
Protein synthesis occurs in the cell. The code to copy the exact sequence of construction of a protein is retained within the cell structure. The mechanism by which this is done is very complex and involves messenger RNA (mRNA), transfer RNA (tRNA) and ribosomes but the result is the definite order of amino acids to produce a particular protein maybe many hundreds or thousands of amino acid units in length. There is nothing random about the synthesis of protein.
An interesting question arises concerning the formation of the actin/myosin, the contractile proteins of muscle. Most proteins are structural in some way and are synthesised by the body to repair and replace damaged tissue, but what causes a large amount of these two proteins to be made in the muscle growth process? Is it to repair damaged muscle that has been stressed that causes this growth? Or some other response mechanism triggered within the body when muscle has been stressed? Clearly though, muscle must be considerably stressed to result in growth. Does (physical not psychological) stress trigger the release of human growth hormone (somatotropin)?
It is important to appreciate that protein synthesis (anabolism) and degradation (catabolism) is taking place constantly. This is generally known as metabolism, but involves both synthesis and degradation. Once a protein has been constructed it will not exist in that form forever. New and identical protein will replace older protein which is broken down into the constituent amino acids and these acids reused to form new and different protein. The amino acid pool. This process ensures that newly ingested protein through diet and amino acids already in the body are always available to synthesise any protein necessary for the survival of the life form. All protein-containing body tissue is constantly being regenerated. Over a variable period, every cell-type has died off and been replaced by a new one. The single cell is a complete entity capable of replication (reproducing itself). The human body is a mass of countless billions of different cells which coexist as the human and the particular collection of cells distinguishes the human from any other animal species. Cells die off but are replaced with new ones. The dead material is eventually removed from the body.
In the normal mixed diet it is not likely that any particular amino acid will be deficient. In most sources of animal protein all the amino acids are present, but in differing amounts. It is difficult to estimate the actual levels without knowing the exact sequence of amino acids in any specific protein since thousands of different proteins are probably present in total. However, if 1.5g/kg protein were used as a guide then 120g of protein would be the daily intake for someone of 80kg body weight. Obviously, with increased body mass (of muscle) then the greater the level of protein that must be consumed.
posted by Louis Brothnias @ 9:41 AM
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