Diagnostic Characteristics
Bacteria are prokaryotic, and make up the majority of most known prokaryotes. Bacteria have no nuclear envelope, membrane enclosed organelles, or histones for DNA. Unlike archaea, the other prokaryotic domain, Bacteria have peptidoglycan in their cell walls, and only have one kind of RNA polymerase. Bacteria have unbranched hydrocarbons, and unlike archaea, have Formylmethionine as the interior start amino acid for protein synthesis, instead of methionine. Bacteria also have circular chromosomes, like archaea, but cannot grow in temperatures above 100 degrees C and have growth inhibited in response to the antibiotics streptomycin and chloramphenicol. Lastly, bacteria rarely have introns in their genes, like archaea and eukarya do.
Bacteria can be found almost anywhere. Bacteria live in almost all habitats except the most extreme areas, where the other type of prokaryote archaea are found instead.
Major Types
Proteobacteria is a large roup of bacteria that contains five subgroups. These subgroups are Alpha Proteobacteria, which are either mutual symbionts or parasites, Beta proteobacteria, which are important to recycling nitrogen by oxidizing ammonium and producing nitrite, Gamma Proteobacteria, such as sulfer bacteria and Escherichia coi, Delta Proeteobacteria, such as the myxobacteria that are known for secreting substratum so that they can move around, and Epsilon Proteobacteria, which are related to the delta group and are seen in bacteria such as Helicobacter pylori. Another group of bacteria is the Chlamydias. This is a group of parasites that only live in animal cells. They depend on the cell for everything they need to survive. The third group is Spirochetes. A lot of these types of bacteria are free living, and some are pathogens. Spirochetes are helical in shape and are heterotrophic. The forth group is Gram-Positive bacteria. This group also contains subgroups, such as actinomycetes, which are important in medicine and are known to form colonies with branched chains of cells, and spore forming groups like Bacillus and Clostridium. Another subgroup is the mycroplasmas, which are usually soil bacteria or pathogens. The last group is Cyanobacteria. This group contains photoautotrophs, and they are the only prokaryotes with photosynthesis that is plantlike and oxygenic.
Basic Anatomy
The basic anatomy of a bacterium consists of a cell wall and cell membrane on the outside, which contains the bacterium. This is all contained in a protective layer called a capsule, which is located outside the cell wall. Also in the bacteria’s outer layer are pili, which are surface appendages that help the bacterium adhere to surfaces. A flagellum is also commonly found on bacteria, and is used for movement. Inside of the bacteria, structures such as DNA, which are found in the nucleoid region, and plasmids, which are smaller rings of DNA. Bacteria also sometimes have specialized membranes for things such as respiration for an aerobic bacterium, or thylakoid membranes for photosynthetic bacteria.
Transport of Materials
The transport of materials in bacteria occurs through passive transport as well as active transport, which requires ATP to move the substance across the membrane. Material transport often uses proteins that are specifically for moving substances across.
Reproduction for bacteria is asexual, which means that the bacterium is the only parent for its offspring and therefore passes on all of it genes directly, usually through binary fission. Binary fission is where the offspring are all identical to their parent, because the parent passed on genes that are identical to its own.
Environmental Adaptations
A major adaptation that some bacteria have is endospores. An endospore is a resistant cell that is for withstanding harsh conditions that the bacterium may be in, such as boiling water. Endospores are formed by the original cell replicating its chromosome and one copy is surrounded by a wall. The endospore is then revealed by the outer cell disintegrating.