Protein - The Basics

PROTEIN

Protein is a macro nutrient composed of upto 21 amino acids and is the only macro source of nitrogen in the diet. Amino acids consist of an amino group, a carboxyl group, a hydrogen atom, and a distinctive R-group, all bonded to a carbon atom. Many amino acids join together by peptide bonds to form a polypeptide chain.

In 1953 Frederick Sanger determined the amino acid sequence of insulin, a protein hormone. This was a landmark discovery because it showed for the first time that a protein has a precisely defined sequence which determines its function. Each protein has a unique, precisely defined amino acid sequence.

The human body can make the majority of the amino acids however 9 of these are impossible to synthesise and so have to be taken in through the diet and are thus termed essential amino acids. Without them you would degenerate and die, it is as simple as that.

Over 50% of the dry weight of your body is protein and all bodily functions are controlled by enzymes which are also proteins. Protein is therefore undoubtedly a key nutrient for the human body.

Over 98% of the molecules that make up the human body are completely replaced each year. The body you have today is built almost entirely from what you have eaten over the past six months. The well-known saying "you are what you eat" is founded on the fact that the body is in a constant state of change at the chemical level. Protein is the primary building material for the human body, remove the water from the muscle and nearly everything that is left is protein. Consequently, eating the correct levels of protein is essential. The quality of the protein that you eat is also important, if you eat poor quality protein then all of the structures of your body synthesised from that protein will be poor quality.

There are two key questions to be answered here:

-How much protein do you need to take in?

-What is good quality protein?

The amount of protein required in a diet varies dramatically between sedentary individuals and athletes. This is because protein is used for energy providing 5-10% of the total energy supply during intense training. Also, protein is lost from the body in sweat and hemolysis (death of red blood cells) which increase substantially during exercise.

So, how much protein is needed for athletes?
A very high protein intake will maintain a highly positive nitrogen balance which is necessary for the building of muscle. However, it is not simply the protein that you eat that controls the use of nitrogen for muscle building. Such use is controlled by the processes in the liver that holds the available store of amino acids at precisely the level required to meet bodily demands. Any excess protein is simply broken down into carbohydrates and urea. It is therefore bodily demand that dictates how the protein you eat will be used, not the amount of protein taken in itself. If you take in masses of protein in the hope that it will build muscle you will see little in the way of results as any protein ingested in excess of what your body currently believes it needs, will simply be passed out of the body in the urea. Muscle growth is caused by the trauma of intense exercise. Following intense training your body will recognize that it is in need of more protein than it previously required and so any extra protein ingested will be utilised as opposed to expelled. Any use of anabolic growth agents such as steroids causes a rapid buildup of nitrogen balance and protein within the cells and your demands fro dietary protein dramatically increase.

The trick is therefore to match your protein intake to your training program.

Protein does nothing to stimulate growth, it simply provides the necessary materials for growth which is stimulated by the trauma placed on muscles during training. Preceeding growth, it only makes sense that there must be some form of stimulation for growth to occur.

BIOLOGICAL FUNCTIONS OF PROTEIN
Proteins play crucial roles in virtually all biological processes.

Enzymatic Catalysts
Nearly all chemical reactions in biological systems are catalysed by specific macromolecules called enzymes -nearly all enzymes are proteins, therefore proteins are central to determining the pattern of chemical transformations in biological systems such as the human body.

Transport and Storage
- Myoglobin (a protein) transports oxygen in muscles.
- Coordinated Motion
- Proteins are the major component of muscle and muscle contraction occurs by the sliding motion of two kinds of protein filaments.

Mechanical Support
The high tensile strength of skin and bone is due to collagen, a fibrous protein.

Immune Protection
Antibodies are highly specific proteins that recognise and combine with foreign substances and are therefore vital in distinguishing between self and non-self.

Generation and Transmission of Nerve Impulses
- The response of nerve endings to certain stimuli is controlled by specific receptor proteins.
- The remarkable range of functions mediated by proteins results from the diversity and versatility of the amino acids which are the building blocks of protein.