Prokaryotes are divided into two domains: Archaea and Bacteria. Archaea and Bacteria have two different evolutionary histories. Nevertheless, Archaea and Bacteria share some fundamental similarities that make them prokaryotes and not eukaryotes. Prokaryotes tend to be much smaller than eukaryotic cells, lack membrane-bound organelles, and have only one circular DNA molecule. Prokaryotes also inhabit some of the most extreme environments on Earth. Most prokaryotes are chemoheterotrophs, getting their energy and carbon from other organisms. Prokaryotes, though small and inconspicuous, play extremely important roles in our lives and in the greater ecosystem!
Bacteria: One of two domains for prokaryotes, includes some organisms that cause human diseases.
Cyanobacteria: A phylum of bacteria that obtain energy through photosynthesis.
Gram Staining: A way to classify bacteria based on the ability to retain a purple dye.
Gram-Positive Bacteria: Bacteria able to retain the dye.
Gram-Negative Bacteria: Bacteria do not retain the dye.
Archaea: One of two domains for prokaryotes that includes organisms living in extreme environments.
Extremophile: Any type of Archaea that lives in an extreme environment, such as a very salty, hot, or acidic environment.
Plasmid: Small, circular piece of DNA in prokaryotic cell.
Flagella: Tail-like structures that protrude from the plasma membrane of some prokaryotes.
Endospore: A spore that forms inside prokaryotic cells when under stress.
Genetic Transfer: How prokaryotic cells acquire new genetic material and thus increase the genetic variation in the population.
Bacteria is a domain of single-celled prokaryotes.
Cyanobacteria are very important bacteria that undergo photosynthesis and release oxygen into the atmosphere
Gram staining is one method used to classify bacteria. Bacteria are differentiated into Gram-positive and Gram-negative based on the ability to retain a purple dye. The ability to retain the dye depends on the type of cell wall and outer membrane the bacterium has.
Gram-positive bacteria stains purple with Gram stain. This is because they have a thick cell wall without an outer membrane. Example: Cyanobacteria
Gram-negative bacteria stains red with Gram stain. this is because they have a thin cell wall with an outer membrane. Example: Salmonella
Archaea is the second domain of single-celled prokaryotes.
Prokaryotic cells can be distinguished by shape. The three most common shapes are helical (Spirilli), spherical (Cocci), and rod-shaped (Bacilli).
Prokaryotic structures include:
Endospores are special structures that form when a prokaryote is under stress. These spores are tough structures that enclose the DNA and protect it. The prokaryote enters a dormant state that help the cell survive for long periods of time.
Prokaryotes reproduce by binary fission, a type of asexual reproduction in which a parent divides into two genetically identical daughter cells. Binary fission begins with the duplication of the genetic material (chromosome and plasmids) and is followed by cytokinesis, the division of the cytoplasm.
One really important role bacteria play in the ecosystem is as decomposers. They recycle organic compounds back into inorganic compounds and basic nutrients.
Since the parent and offspring are exactly the same in binary fission, there is no genetic variation. This would increase the risk of extinction.
Prokaryotes increase genetic variation by genetic transfer. The cells can take up foreign DNA in the environment or directly exchange plasmid with other prokaryotic cells.
Bacteria also produce important products that have significant implications for human health. For example, bacteria make antibiotics and vaccines along with ethanol and certain enzymes.
Bacteria also lay at the root of many familiar diseases, for example, tetanus and food poisoning. One way people try to fight off bacterial infections is through the use of antibiotics. However, the overuse and misuse of antibiotic drugs has also led to antibiotic resistance, or the evolution of antibiotic-resistant bacteria.