An Introduction to Molecular Biology
The cell constitutes the basic structure of all living organisms (
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.