# Structural Biochemistry/Bacteria

Bacteria belong to the subgroup of prokaryotic microorganisms. They can be found in many habitats on the planet, living bodies of plants and animals, and organic matter as well. There are approximately 40 million bacterial cells in a gram of soil and this amount in one milliliter of fresh water is a million. Bacteria, due to its widespread presence, have the largest biomass on Earth.
Structure
Intracellular structure A lipid membrane surrounds the bacterial cell. This membrane defines the shape of the cell as it encloses all of its internal components and also keeps all the essential nutrients, proteins, etc. within the cytoplasm. Since bacteria are defined as prokaryotes, they do not have membrane-bound organelles and also miss some of the eukaryotic organelles such as the endoplasmic reticulum and the Golgi apparatus. Genetic information of bacteria is stored in the nucleoid which contains a single circular chromosome with RNA and associated proteins. Ribosomes are found in bacteria to help produce proteins; however, their structures differ from those of eukaryotic cells and Archaea.
Extracellular structure On the outside of the cytoplasmic membrane of the bacterial cell, a cell wall is present. Its material usually is peptidoglycan. The cell wall serves as the front and most important line for protecting the cell from being attacked by outside chemical reagents such as antibiotics. There are mainly 2 types of cell wall –Gram-positive and Gram-negative. Gram-positive bacteria’s cell walls are thicker than those of Gram-negative ones which are the case in most bacteria. In addition, an S-layer made of proteins covers the outside of cell. This acts as a macromolecular diffusion barrier. Other extracellular components include: • Flagella, rigid protein structures, help cells with mobility. Its driving force by the energy released by the transfer of ions down an electrochemical gradient across cell membrane. • Fimbriae, fine filaments of proteins, are involved with attaching to solid surfaces or to other cells.
Endospores They are dormant, tough structures made by certain bacteria. The reason for the formation of endospores (usually happening in Gram-positive bacteria) is due to the deficiency of nutrients. Metabolism Many different metabolic types are adopted by bacteria. Three major criteria defining the characteristic of each type (nutritional type) of bacterial metabolism are the energy source, the carbon source, and the electron donors used for growth. In phototrophs, sunlight is used as the source of energy. In lithotrophs, inorganic compounds are the energy source. Lastly, organic compounds are what provide energy for organotrophs metabolism to take place. In all three nutritional type, organic compounds and carbon fixation are the sources of carbon.
Growth and reproduction Bacteria, after growing to a set size, would go through binary fission to reproduce themselves. This type of reproduction is asexual. Bacteria’s reproduction rate can be as much as double the population every 9.8 minutes under optimal conditions. In addition, some kinds of bacteria can also produce in a more complex method by have more evolutionary structure that help form new daughter bacterial cells.