Latest update: 29/06/2017


The human organism is controlled by a code that we call DNA, which is short for DeoxyriboNucleic Acid.
It is present in (almost) all our cells.

DNA is a chain (in humans) of billions of nucleotides (or bases) arranged in a specific sequence. There are only four different bases: adenine (A), cytosine (C), guanine (G) and thymine (T).

These are joined in a constantly changing sequence to a chain of sugars and phosphates, thereby forming a long chain.
They occur in pairs and every base is joined to another base (always the same one):

  • A is always joined to T (and T to A);
  • C always to G (and G to C).

In other words DNA forms a double chain that looks like a rolled-up spiral ladder. Each pair of bases forms a single rung on this ladder. This is the so-called double helix structure of DNA (see the diagram).
The bonded nucleotides - always in groups of three (see genes) - are responsible for making all the amino acids in our body. Amino acids join together to form proteins, and these are in turn needed to build or repair cells and tissues.

In short: the long DNA code controls our whole organism, so those four letters form the basis for all human life.

Introduction DNA

Our body - every body, every living being - is made up of cells, just as a building is made up of bricks. Humans have many millions of cells, somewhere in the region of ten trillion (ten followed by twelve zeros).
Every cell contains a nucleus surrounded by cytoplasm, which is in turn enclosed in a cell membrane.
The cytoplasm contains a number of organelles, such as mitochondria (the tiny power plants of our body) and lysosomes (the 'wasteprocessing plants' in our cells).
We will come back to these in the biochemistry laboratory.
The nucleus contains nuclear DNA (from the word nucleus), and the mitochondria contain mitochondrial DNA.

Our DNA stores the programming code that determines the structure and function of our bodies.
The DNA code is different for all living beings, with the exception of identical twins.
This being said people in the same family do usually share a number of characteristics: their eye or hair colour, physical build, level of intelligence, susceptibility to particular diseases, etc.
This phenomenon occurs as a result (sometimes an unpleasant result) of our genes.

In short, although the genome of every person on earth appears almost identical, there are tiny differences that make each one of us unique. These are also what make us similar (in some ways) to our blood relatives, since we share certain characteristics.
These small but specific DNA mutations that can occur indifferent members within a single family allow us to trace someinherited diseases very precisely.