Virus particle used for gene therapy

What are genes?
All living organisms consist of cells. Very simple organisms like bacteria or amoebae consist of one cell only. This cell has to perform all the tasks necessary to stay alive. Complex organisms like people consist of billions of cells and hundreds of different cell types. Different cells perform different tasks. Yet, to a large extend the cells are autonomous, managing their own growth, energy and survival just like the amoeba.

The cells can function largely independently, because each cell contains a complete copy of the genome. The best analogy for the genome is a cookbook, A large collection of recipes (the genes) each describing how to perform a specific task. Some genes describe tasks that are essential for every cell in the body, e.g. how to burn fuel for energy. Other genes describe tasks that are only done by specific cells. E.g. the genes that describe how to make the light sensitive machinery are only used in the photoreceptor cells, the light detecting cells in the retina.

What happens if a gene is mutated, in other words if it does not describe the task properly? If it is a gene of universal importance like that burning of fuel, the defect will be lethal, because none of the cells in the body can function properly. But a mutation in a gene that is only used by specialised cells will often lead to disease. Sometimes it is quite mild, while for other genes the results can be more serious. A defect in the gene for rhodopsin, a light sensitive chemical, means that the photoreceptor cell cannot make rhodopsin; therefore it cannot react to light, resulting in visual impairment.

This page last modified 18 December, 2012 by xxx