Life

Biology

Bacteria or prokaryotes are the most common living beings on Earth: one spoonful of soil can contain, for instance, up to 10,000 billion bacteria. They are unicellular organisms, i.e. they consist of one cell only. They are very small in size, since a large part of bacterial cells have a diameter of 1 to 10 microns (one micron equals one thousandth of a millimetre), so an orderly row of one thousand bacteria would be just one millimetre long. Bacterial cells, unlike the cells of superior organisms (eukaryotes), do not have organelles enwrapped in membranes (nucleus, Golgi apparatus…) or chromosomes. Chromosomes are structures made of DNA wrapped around proteins, called histones, and their purpose is to make the long DNA molecules contained in the nucleus more compact and orderly. Chromosomes are essential since they arrange the large amount of genetic material contained in eukaryote cells: if, for instance, the DNA contained in just one human somatic cell were unwrapped, the resulting molecule would be approximately two metres long! In bacteria, instead, the DNA is not contained in a nucleus and is round in shape. Another specific feature of bacteria is their protective structure (the wall) that enwraps and encloses the whole cell. The cellular wall is composed of proteins and sugars and, as well as protecting the micro-organism, it puts the cell in contact with the external environment and the other bacterial cells.