Bacteriae, genetic structure

The actual bacterial DNA, which carries the genes characteristic of the respective bacterium and important for its survival, is also referred to as the "bacterial chromosome". In bacteria, the entire genetic structure is stored on a single ring-shaped chromosome (nucleotide) in the form of double-stranded DNA. The exceptions to this rule are Helicobacter pyloris, Borrelia burgdorferi & some others; they have a linear chromosome. Neisseria have a double set of chromosomes, each with a different set of genes. Remark: Ring-shaped chromosomes do not need telomeres for replication.

The best characterized bacterial chromosome is that of Escherichia coli. It consists of a single circular DNA molecule about 4.7 x 106 base pairs long. In addition, bacteria can contain extrachromosomal DNAs, called plasmids, which have additional genes. Finally, bacteria can be infected by bacteriophages, whose genetic information usually causes the destruction of bacterial cells. The DNA chain of a bacterium is about 1mm long and contains about 5x105 base pairs with about 500 genes. The human genome is 2m long and comprises about 3x109 base pairs with about 25,000 genes.

Bacterial DNA lies almost naked, without the protection of histones and without a nuclear membrane in the cytoplasm. Thus, since bacteria have only one nuclear equivalent and no true nucleus, they are called prokaryotes. The DNA in stretched form would be clearly too long for the bacterial cell. It must therefore be compactly entangled. This energetically unfavourable measure only succeeds through the enzymatic activity of gyrases. The bacterial gyrase differs from the topoisomerase II of the eukaryotic cell, which has the same task there, so that it can be selectively inhibited (gyrase inhibitor).

The cells of the human immune system are able to bind bacterial DNA fragments with multiple CpG motifs (so-called CpG oligonucleotides, p=poly) with their Toll-like receptor, which leads to a stimulation of cytokine production and antibody production.