Amino acids - the building blocks of protein
Brian Mackenzie provides an overview of the role and function of amino acids and protein
During the process of digestion the proteins in our food are broken down into their constituent amino acids which are in turn absorbed by the blood capillaries and transported to the liver. The amino acids are then synthesized into proteins or stored as fat or glycogen for energy. Each gram of protein produces approximately 4 Calories. Many proteins function as enzymes and others:
All proteins are broken down into single amino acids by the digestive enzymes in either the stomach or in the small intestine and then reassembled into the specific new proteins by other enzymes within the body. The cells within the digestive tract can only absorb single amino acids, known as free form, and very small chains of two or three amino acids called peptides. In the same way that glycogen is made up of many molecules of glucose put together, protein is made up and linked together by many amino acids. These amino acids are linked together in long and varied chains by peptide bonds. The types of peptide bonds are:
A combination of more than 100 amino acids joined by peptides finally forms a protein.
Amino acids are the building blocks of protein. The formation of protein can result in dehydration because water molecules are lost as amino acids combine to form more complex molecules. The body requires 20 different amino acids of which 8 are referred to as essential amino acids which cannot be synthesized by the human body. Animals and plants manufacture proteins which contain these essential amino acids. Non-essential amino acids can be synthesized by body but this does not mean they are unimportant, they are, it is just that the body is capable of producing sufficient to meet the demands for growth and tissue repair. It is therefore important that our diet contains appropriate levels of protein.
Essential Amino Acids
There are 8 essential amino acids. These are the amino acids that the body must obtain on a daily basis through the foods we eat. The essential Amino Acids are:
Nonessential Amino Acids
There are 14 nonessential amino acids. These are the amino acids that the body produces itself in the liver through a process known as transamination. Being called nonessential does not mean that these amino acids are unimportant. They form from compounds that are already in the body at a rate that meets the needs of normal growth and tissue repair. The non-essential Amino Acids are:
*Histidine is essential for babies but not for adults.
Recommended Protein Intake
Despite the beliefs of many coaches and athletes, eating excessive protein provides little benefit. Protein intake significantly above the recommended values can prove harmful because excessive protein breakdown strains the liver and kidney functions through the production and elimination of urea and other solutes.
The recommended daily allowance for men and women:
Source of Protein
Proteins that contain all the essential amino acids in approximately the right proportions for your body's requirements are sometimes called 'high-biological-value' proteins. These are found in foods that are derived from animals:
Complete and Incomplete Proteins
Animals and plants provide us with proteins that contain essential amino acids. There are no health benefits or physiological advantages from an amino acid that comes from an animal as opposed to that which comes from a vegetable. However, because an animal's body is similar to human being's, its proteins contain similar combinations of amino acids which mean that our bodies absorb these proteins more efficiently than other proteins. These are known as high quality, or complete proteins, as they contain ample amounts of all the essential amino acids.
Sources of complete Proteins are:
With the only exception of soybeans, the following sources of protein have limited amounts of some amino acids, so are not easily absorbed by the body and cannot be used as efficiently as animal proteins. These are known as incomplete proteins as they limit the combinations of other proteins that can be produced from them.
Sources of Incomplete Proteins are:
Training and Protein Needs
Research suggests that protein breakdown increases during and immediately after exercise, and that protein manufacture slows down at the same time. The more intense the exercise, the greater your protein breakdown will be, and the greater your needs will become. If you train to increase muscle mass, your protein needs will be greater still. Extra protein will be needed not only to compensate for protein breakdown but also for new protein to be made and for muscle growth. It is important to realise that a high-protein diet alone will not lead to any increase in strength or muscle size. It is only when it is combined with heavy resistance exercise that additional protein can cause this to happen.
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About the Author
Brian Mackenzie is a British Athletics level 4 performance coach and a coach tutor/assessor. He has been coaching sprint, middle distance and combined event athletes for the past 30+ years and has 45+ years experience as an endurance athlete.
The following Sports Coach pages provide additional information on this topic: