An Introduction to Molecular Biology

The cell constitutes the basic structure of all living organisms (cellula in latin means small chamber). The typical diameter of a cell is 10–100 micrometers (μm), its volume around 10 picoliters (pl) and its mass around 1 nanogram (ng).

Cells can be divided in two main groups. Prokaryotic cells, such as bacteria, lack nucleus and are unicellular organism, characterized by a relatively simple organization with only one compartment containing a circular DNA molecule. Eukaryotic cells are characterized by a nucleus and a cytoplasm containing many sub-cellular compartments. The nucleus is surrounded by a nuclear envelope with nuclear pores that allow the transport of macromolecules between the nucleus and the cytoplasm. The DNA molecule is localized inside the nucleus and organized in chromosomes. Some eukaryote organisms are unicellular such as yeasts, but the most part are pluricellular, with the most complex organism being human, with more than 10 000 billion cells.