Prokaryote means “before a nucleus.” They are single-celled organisms and the smallest, simplest organisms.
This kingdom is subdivided into two kingdoms:
I. Archaebacteria - Found in anaerobic conditions with high salt concentrations, high temperatures and a low pH. These are believed to be the conditions on the primitive Earth. Earth’s early atmosphere didn’t contain oxygen. (anaerobic) Scientists believe that all life kingdoms are descended from this group. Archabacteria’s phyla are based on their habitats.
Anaerobic Methanogens - live in the gut of animals, swamps and marshes and produce all of the methane gas found in the Earth’s atmosphere.
Nutrition means obtaining energy and a source of carbon to produce the organic compounds needed for cellular metabolism.
Most eubacteria are heterotrophs and obtain energy by breaking down organic molecules from their environment. Some are parasites , absorbing nutrients from living organisms. Others are saprobes , decomposing dead organic matter.
Some eubacteria are autotrophs and produce their own organic compounds. (example- cyanobacteria (blue-green bacteria) are photoautotrophs using light for energy, but they lack true chloroplasts.
Chemical reactions take place on the inner surface of the cell membrane so that gases can pass into and out of cells easily.
All living things must carry out cellular respiration to receive energy. Bacteria differ in whether or not they require oxygen.
If respiration requires oxygen, bacteria are termed aerobes . If oxygen is absolutely necessary for survival they are called obligate aerobes.
Bacteria that carry out respiration without oxygen are called anaerobes. Presence of oxygen kills some bacteria and these are called obligate anaerobes. (example- Clostridium botulinum produces toxins that can cause an extreme form of food poisoning called botulism.)
Another group of bacteria can survive with or without oxygen and they are called facultative anaerobes .
Bacteria reproduce asexually and divide by the process of binary fission . In binary fission, the parent cell divides into two offspring cells that are completely identical. There is no exchange of genetic material so the process is asexual . (example- E. coli produces between 10 and 100 million bacteria in 12 hours.)
When conditions begin to fail, either through decrease of food or space, or cooler temperatures, some bacteria take part in a type of sexual reproduction called conjugation. In conjugation the two cells join briefly and one cell donates some DNA (called plasmid) to the other one. Sexual reproduction combines genetic information from two different individuals and increases variation.
Ex. - Antibiotic resistance in the 1950’s.
Genetic recombination in several groups through the use of pili (minute tubes that allow the passage of the bacterial chromosome from the donor cell to the recipient cell
When growth conditions become extremely unfavourable, many gram positive bacteria form structures called endospores. Endospores are DNA and a small amount of cytoplasm enclosed in a tough cell wall. They are resistant to extremes in temperature, drying, and harsh chemicals.
Bacteria convert atmospheric nitrogen into a useable form of nitrogen. (nitrogen-fixers)
Bacteria play an important role in recycling by breaking down dead and decaying organic matter. Used to eliminate or neutralize toxic and hazardous waste and spills. Also used in sewage treatment to decompose the 5 billion kg of solid waste produced daily.
Bacteria is used to produce dairy foods that help maintain a healthy balance of microorganisms in the digestive system.
Only a small percentage of prokaryotes are pathogenic, or disease causing. These bacteria produce deadly toxins in the human body that cause disease symptoms. Endotoxins are seldom fatal and cause fever, vomiting and diarrhea. E. coli , Salmonella. Exotoxins are highly toxic, do not cause a fever and are often fatal. Tetanus and botulism.
Example- Toxins released by the bacterium Streptococcus pneumoniae may result in symptoms of pneumonia.
B . Class Cyanobacteriae—The Blue-Green Bacteria 1. Introduction a. Pigments 1) Chlorophyll a 2) Phycocyanin 3) Phycoerythrin b. Can both fix nitrogen and produce oxygen 2. Distribution a. Widely distributed in fresh and marine waters b. Some precipitate carbonate deposits (travertine)
3 . Form, metabolism, and reproduction a. Form 1) Cells often occur in chains or hair-like filaments 2) Some species occur as colonies 3) Color varies depending on pigments present, although half are blue-green b. Metabolism • store carbohydrates, lipids, and the nitrogenous cyanophycin c. Reproduction 1) New cells formed by fission 2) New colonies may be formed by fragmentation at: a) Heterocysts (nitrogen-fixing cells) b) Akinetes 3) Genetic recombination
4. Blue-green bacteria, chloroplasts, and oxygen a. Symbiotic origin of chloroplasts from blue-green bacteria • blue-green bacteria occur symbiotically and function essentially as chloroplasts in host organism b. Speculation that chloroplasts originated as prochlorobacteria 5. Human relevance of the blue-green bacteria a. Occur at bottom of food chains b. Production of blooms c. Poisons d. Spirulina used as food e. Undesirable effects in human water supplies f. Nitrogen fixation
In isolation, viruses and bacteriophages show none of the expected signs of life. They do not respond to stimuli, they do not grow, they do not do any of the things we normally associate with life.
Strictly speaking, they should not be considered "living" organisms at all. However, they are more complex than a lifeless collection of macromolecules and they do show one of the most important signs of life: the ability to reproduce at a fantastic rate but only in a host cell .
Candidates for the original sources of viral genomes include plasmids and transposons.
Plasmids are small, circular DNA molecules that are separate from chromosomes.
Plasmids, found in bacteria and in the eukaryote yeast, can replicate independently of the rest of the cell and are occasionally be transferred between cells.
Transposons are DNA segments that can move from one location to another within a cell’s genome.
Both plasmids and transposons are mobile genetic elements.
D . Viral Reproduction 1. Viruses replicate only at the expense of their host cells 2. Viruses must become attached to a susceptible cell 3. Once inside the host cell, their DNA or RNA directs the synthesis of new viral particles 4. Some viruses mutate rapidly 5. Viruses may affect the metabolism of their host cells 6. Infected cells can produce interferon which protects uninfected cells
HIV doesn’t target just any cell, it goes right for the cells that want to kill it. “Helper" T cells are HIV's primary target. These cells help direct the immune system's response to various pathogens.
After many years of a constant battle, the body has insufficient numbers of T-Cells to mount an immune response against infections. At the point when the body is unable to fight off infections, a person is said to have the disease AIDS .
It is not the virus or the disease that ultimately kills a person; it is the inability to fight off something as minor as the common cold.