Bacterial Cell Structure and Nutrition

Bacterial Cell Structure and Nutrition

A typical bacterial cell is enclosed by a cell wall and, within it, a plasma membrane, surrounding the cytoplasm in which the cell's metabolic activities take place. Unlike the cells of plants and animals, a bacterial cell has no nucleus bound by a nuclear membrane; instead, its single, usually circular, DNA molecule lies free in the cytoplasm in a region called the nucleoid, and this bacterial 'chromosome' is often referred to as a genophore, since it plays the role of a chromosome without having the membrane-bound, protein-associated organisation of a true eukaryotic chromosome.

In addition to this main genophore, many bacteria carry one or more small, circular pieces of extra-chromosomal DNA called plasmids. Plasmids replicate independently of the main bacterial chromosome and typically carry genes that are useful but not strictly essential for everyday survival - for example, genes conferring resistance to antibiotics. Because plasmids can be transferred between bacterial cells and can be engineered to carry a chosen gene, they are of great practical significance as vectors in genetic engineering and biotechnology.

During conjugation (see the next section), a donor bacterial cell extends a tube-like structure called a sex pilus to make contact with a recipient cell; the sex pilus draws the two cells together and provides the physical channel through which DNA (often carried on a plasmid) passes from donor to recipient. …