Professor Hayflick of the University of California, San Francisco, showed in the early 1960s that cells (he was using human connective tissue cells) in a laboratory dish, which were kept well-nourished and at optimum temperatures and conditions, would continue to divide up to around 50 times, after which they would start to die. When cells from older people were taken and treated in the same way they divided fewer times compared with embryonic cells, which when cultured divided more often. In all cases, whether the cells came from embryos or middle-aged or old people, they always reached a point in time when for no apparent reason their ability to divide and reproduce themselves declined, and they ultimately died.

What does a cell do while it is functioning?
Most of our body cells have unique and specific tasks to perform. They are not unlike integrated factories in which a constant supply of raw materials is delivered, entering via the cell membrane (factory gate) which keeps out what is undesirable and lets in (and out) what is needed, including fatty acids and glucose for energy production (fuel). Fuel for energy is essential so that a wide array of different substances can be manufactured, which will then be used or stored by the body, including proteins for the repair or building of tissues, energy storage molecules such as polysaccharides, and various fats and information storage units deoxyribonucleic acid and ribonucleic acid (DNA and RNA).

In order for the manufacture to take place accurately and efficiently a number of protein catalysts are essential at each stage of manufacture (catalysts are substances which take part in chemical processes but which are not themselves used up by the process). It is known that up to 200 million protein molecules, some used as catalysts, others in the structural creation of new molecules, are involved in this whole process, and exist together inside each cell. Each and every one of these proteins will have been encoded with their particular characteristics, uses and functions by DNA (genetic instruction and information messages).

Since proteins are made up of collections of building blocks called amino acids, the unique structure and attributes of each protein is decided by which of the twenty or so amino acids they contain~and the order in which these 'building blocks' are assembled. Each protein has different quantities and ratios to those found in another protein. This is why kidney cells are not me same as blood cells, and why brain tissue is not the same as skin. All are protein-based but each is different, and it is the DNA encoding which tells the cells which amino acids and what ratios and quantities of these to assemble in order to create that individuality.

This whole protein manufacturing process is carried out in the cytoplasm of the cell while the DNA is kept safely tucked away in the nucleus of the cell. So, whenever a new protein is required (a constant process) for use as a structural unit in the tissue of an organ or part of the body, it is necessary to send instructional blueprints from the nucleus DNA (the master copy) to the cytoplasm (from the central office to the factory floor so to speak). This is achieved by sending copies of that part of the DNA which is required, from the nucleus to the cytoplasm, as a plan containing separate instruction information on RNA (ribonucleic acid) molecules. This messenger RNA then acts as a blueprint/template from which the new protein is designed and manufactured in a unit of RNA/protein called a ribosome (just like a specific machine tool).