Bacteria are the world’s most common organisms, with an estimated five nonimillion bacteria on Earth. They come in a variety of shapes and sizes. The largest bacteria is half a millimeter long and the smallest is just 0.3 microns across. General size is between 0.5 microns and 5.0 microns. The characteristics of bacteria are among the most varied in any domain of life- the relatedness between 2 species of bacteria is often much less than the relation between any 2 given metazoans, say a human and a slug. Many structural features are unique to bacteria and are not found among archaea or eukaryotes. Due to the simplicity of bacteria compared to larger organisms, the cell structure of bacteria has been well studied, revealing many biochemical principles that have been subsequently applied to other organisms. Even though they infect and can kill billions of other organisms, bacteria have a relatively simple structure.
The most elemental structural property of bacteria is Cell morphology (shape). Cell shape is generally characteristics of a given bacteria, but can vary depending on growth conditions. Bacteria generally form distinctive cell morphologies when examined by light microscopy. Theses are often the first characteristics observed by a microbiologist to determine to identity of an unknown bacterial culture. The examples are as follows.
The most obvious structural characteristics of bacteria are their small size. For example, Escherichia Coli, commonly known as E.coli cells, an average sized bacterium are about 2 micrometers and 0.5 micrometer in diameter, with a cell volume of 0.6-0.7 micrometer. Small size is very important because it allows for a large surface area-to-volume ratio which allows for rapid uptake and distribution of nutrients and excretion of wastes.
As in other organisms, the bacterial cell wall provides structural integrity to the cell. In prokaryotes (group of organisms that lack a cell nucleus), the primary function of the cell wall is to protect the cell from internal pressure caused by the much higher concentrations of proteins and other molecules inside the cell compared to its environment. The bacterial cell wall differs from that of all organisms by the presence of ‘peptidoglycan’, which is located immediately outside the cytoplasmic membrane (biological membrane that separates the interior of all cells from the outside environment). Peptidoglycans are large, structural molecules made of protein carbohydrate. Peptidoglycan is responsible for the rigidity of the bacterial cell wall and for the determination of cell shape. It is relatively porous. There are 2 main types of bacterial cell walls, Gram positive and Gram negative. For both gram positive and Gram negative, particles of approximately 2 nano meters can pass through the peptidoglycan. They are explained as below.
The bacterial cytoplasmic membrane is composed of a phospholipids bi layer and thus has all the general functions of a cell membrane such as acting as a (barrier which prevents the harmful substances from passing through) permeability barrier for most molecules and serving as the location for the transport of molecules into the cell. Bacteria can have a variety of fatty acids within their membranes.