Protein and amino acid Basics
Protein and amino acid Basics
By Jamie Hale
Protein is a molecule composed of amino acids joined together by peptide bonds. Protein consists of the elements carbon, hydrogen, oxygen, nitrogen and sulfur.
Protein is found in the structure of all living organisms. Protein also play many other roles in the body including enzymatic structures, immunoglobulins- also called antibodies, protein hormones- chemical messengers, in blood some amino acids help maintain blood acid-base balance, protein act as carriers to transport various ions or molecules across cell membranes or in the blood. Proteins display an incredible diversity of functions, yet all share the common structural feature of being linear polymers of amino acids.
Although more than 300 amino acids have been described in nature we commonly refer to 20 amino acids constituting mammalian proteins. (these are the amino acids coded for in the cell). Each amino acid (except proline) has a carboxyl group, an amino group, and a distinctive R side chain (R-group) bonded to the alpha carbon atom. The nature of the side chain ultimately dictates the role an amino acid plays in a protein.
Essential amino acids, also called indispensable amino acids must be supplied in the diet either as free amino acids or as constitutes of protein. These amino acids are no made in adequate amounts in the body to supply needs, thus dietary ingestion is required
Essential Indispensable amino acids include- Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, Valine (Leucine, Isoleucine, Valine or Branched Chain amino acids). The branched chain amino acids (BCAAS) are named so because they have a carbon chain which deviates or branches from the main linear carbon backbone. The BCAAS are metabolized primarily by the peripheral tissues rather than by liver. BCAAS have been shown to stimulate Mtor pathway (pathway enhances muscle protein synthesis).
Creatine monohydrate is an amino acid derivative that is obtained from food and is also formed in the liver from the amino acids arginine, glycine, methionine. Creatine is uptaken by skeletal muscle where it forms phosphocreatine, the high-energy phosphate compound. The amount of phophocreatine in skeletal muscle partially determines the length of time that maximum muscle work can be done.
Conditionally essential, several amino acids can be considered conditionally essential as they are rate limiting for protein synthesis under specific conditions. Conditionally essential amino acids include- Arginine, Cysteine, Glutamine, Histidine, Proline, Taurine, Tyrosine
Glutamine is the most abundant amino acid in human muscle and plasma and is found in relatively high levels in many human tissues. Glutamine constitutes over 50% of highly concentrated amino acid in plasma also making up over 60% of the total intramuscularly amino acids. Glutamine plays various roles in the body including renal aminogenesis, maintenance of acid-base balance during acidosis, nitrogen precursor for the synthesis of nucleotides, cellular fuel in certain tissues, immune system function, and as a direct regulator of protein synthesis and degradation.
Nonessential or dispensable amino acids are made in adequate amounts by the body to meet needs. These amino acids are made from metabolic intermediates as well as other amino acids. Nonessential amino acids include- Alanine, Asparagine, Aspartic Acid, Citrulline, Glutamic Acid, Glycine, Ornithine, Serine.
Proteins are generally to large to be absorbed by the intestine. They must, be hydrolyzed to yield their constituent amino acids, which can be absorbed. Proteolytic enzymes responsible for degrading proteins are produced by three different organs stomach, the pancreas and the small intestine.
Of the three macronutrients protein exhibit’s the highest thermic effect (specific dynamic action). The increase in metabolic rate which occurs following the ingestion of protein is 25-30%. The increase in metabolism results from increased oxidation associated with not only digestion of food, but also absorption, transport, metabolism and storage of energy following eating. The thermic effect of food is also known as diet induced thermo genesis.
Bodily storage of amino acids includes two sites. The first of these is in tissues such as muscle and liver proteins. There also exists a free amino acid pool. The free pool provides amino acids for protein synthesis and oxidation. The sizes of these two sites are considerably different with the bodily protein stores in an average male making up approximately 15% of bodyweight, while the free pool might consist of 100 grams of amino acids. We can also expect an additional 5 grams of free AAs circulating in bloodstream. The free pool is 1% of the size of AA storage in bodily tissue. Various amino acids in the free pool are directly correlated with muscle protein synthesis.
Every day your body is synthesizing and breaking down proteins (referred to as protein turnover). Under normal dietary conditions and individual may turnover 300 grams of protein per day ( this does not imply that 300 grams of ingestion are required per day- large portion of the protein broken is resynthesized)
Athletes protein needs, Peter Lemon suggest the following intakes after looking at protein data 1.2-1.4 g/ kg of protein for endurance athletes, 1.6-1.8 g/ kg of protein for strength athletes. Although there is some research suggesting that higher levels are needed for some people (particularly bodybuilders). There are numerous athletes who have reported higher muscle gains with even higher levels of protein.
There is no scientific data indicating kidney problems when protein intake is above suggested levels. Although people with pre-existing kidney problems could face problems with high levels of protein intake. Also people with metabolic disorders such as Fabrays disease, maple syrup urine diseases, and PKU have different amino acid oxidation properties (need to limit amino acid ingestion).
Champe, P,C. Harvey, R,A. Ferrier, D,A. (2005). Lippincott’s Illustrated Reviews Biochemistry 3rd Edition. LWW.
Dipasquale, M. (1997). Amino Acids and Proteins for the Athlete. CRC PRESS.
Gropper, S,S. (2000) The Biochemistry of Human Nutrition 2nd edition. Wadsworth.
McDonald, L. Protein www.mesomorphosis.com/articles/mcdonald/protein-01.htm
Now available! The book that takes an in depth look at protein and amino acids. The book will include basic protein issues, advanced protein issues and metabolism as well as protein research studies
Description of various amino acids
Protein testing methods
Determining protein needs
What supplement companies don’t want you to know
Amino acids most suited for muscle protein synthesis
Copyright 2005 Jamie Hale