How can understanding your genes lead to a longer, healthier life?
The function and activity of all the cells in your body combine to define what makes you an individual and member of the human race. These activities are controlled and influenced by the genetic content contained in the cells' DNA. The DNA is located on chromosomes within a structure inside the cell called the nucleus - the 'control centre' of the cell. The DNA in a chromosome exists as a double helix, which looks like a 'twisted step ladder'. The sides of the 'ladder' are made up of chains of molecules called nucleic acids. The 'rungs' of the ladder are made up of nucleotide bases, small molecules attached to the chains of nucleic acids by chemical bonds.

In your DNA there are only four types of nucleotide bases: adenine (A), thymine (T), guanine (G) and cytosine (C). These are abbreviated to the letters A, T, G and C. Due to the chemical structure of the four nucleotide bases they bind together in defined sequences to form 'base pairs: G pairs with C while A pairs with T. Each DNA strand within a chromosome is made up of thousands of 'base pairs'. A gene is a unit or sequence of different combinations of the four
nucleotide bases and can be composed of thousands of bases. An individual gene occupies a specific place or locus on the DNA strand on a chromosome and is always found on the same type of chromosome. Every cell has a pair of each of its chromosomes (there are 23 pairs in
total); hence there are two copies of every gene, one in each chromosome.

The diagram below illustrates the structure of your DNA and the sequence of nucleotide base pairs that make up your genes.

Diagram A: How we go from a cheek sample to examining the sequence
of nucleotide bases in your genes

These gene pairs are known as alleles. Your genotype is expressed in terms of your two alleles, which can be identical (homozygous) or slightly different (heterozygous). One copy of your genes is inherited from your father, the other from your mother. The subtle differences between these versions of each gene account for such differences as eye or hair colour.
Within the body almost everything from your hair to your hormones, to the enzymes that control the chemical reactions that digest food, remove toxins, convert nutrients into energy and energy into movement, are either made of proteins (chains of amino acids) or made by proteins. It is your genes that provide the specific code for the formation of your body's proteins, the type of protein that is made, when it is made and what it will be used for within the body.

Enzymes are a special class of proteins; they carry out and control your body's metabolic reactions that can convert food into energy for growth, movement, and other necessary functions. For example, melanin proteins give colour to our hair and eyes, haemoglobin proteins carry oxygen in our blood and myosin proteins make your muscles move. Inside your cells, a gene is transcribed into a messenger molecule within the nucleus. This messenger translates the code from your genes into a chain of amino acids that forms the protein, the actual product of the gene (see diagram B).

Your body can form an infinite number of proteins co-ordinated and controlled by your genes. Small differences in the structure of proteins can make them perform their functions differently or less efficiently. These differences are coded in your genes and they account for the unique differences between individuals and species. These differences are due to naturally occurring alterations in a gene's sequence of nucleotide bases, usually at a single location on the DNA strand and they are referred to as single nucleotide polymorphisms or SNPs (pronounced "snips"). A gene can therefore have multiple forms or polymorphisms. Changes in the sequences of nucleotide bases may also occur in more than one place in a gene. In these cases the general term polymorphism instead of SNP is used to describe the alteration of the sequence in nucleotide bases.

Each person has many single nucleotide polymorphisms, which together create an individual's unique genetic profile. It is these polymorphisms that account for the different levels of activity and efficiency of an individual's genes and impact on the potential outcome of the genes' function (see diagram B).

Diagram B: How genes code for enzymes and how polymorphisms
effect the outcome of their activity.

For your body to produce the proteins needed to function properly, it requires a source of nutrients and effective metabolic processes which are necessary to digest and convert these nutrients into the substances needed by the body. In addition, the body must remove the toxins and by-products that are produced by these metabolic processes in order to ensure that the body remains healthy and efficient.

It is your genetic make-up that determines what and how nutrients are utilised, how toxins are removed, what happens to the by-products produced and how efficient and effective these key processes are within the body.

Your health is a result of how these processes interact with environmental and lifestyle factors such as diet, exercise, stress, smoking and alcohol. By learning about the specific nature of some of your genes, you'll find out how their make-up affects the way in which your body manages these processes and how you can avoid the things shown to have a negative
impact and focus on factors that are of greatest benefit.