Bacteria & Archaea Notes

Prokaryotes are represented by two domains: Bacteria and Archaea.
Living things are divided into three domains:
- Bacteria (Eubacteria)
- Archaea
- Eukarya (Protista, Fungi, Plantae, Animalia)
Archaea size is approximately $1 \mu m$ .

No nucleus.
All single-celled (unicellular).
No membrane-bound organelles.
Reproduce asexually.
The bacterium's chromosome is a single loop of DNA in the nucleoid region.
Many bacteria have one or more plasmids in their cytoplasm.
A plasmid is a small loop of DNA that carries a small number of genes.
Bacteria often have one or more flagella for movement, as well as small hair-like projections called pili.
Bacteria have a complex cell wall composed of peptidoglycan, while the Archaea cell wall is not composed of peptidoglycan.
Some bacteria have a capsule for protection (reduce water loss, resist high temperatures, and help keep out antibiotics and viruses).

The most common forms in both bacteria and archaea are spheres and rods.
They can also take a spiral shape.
Even though most prokaryotes are unicellular, both domains can form aggregations, in which individual cells group together.

Autotrophic bacteria make their own food by assembling complex compounds from carbon dioxide, water, and minerals.
Heterotrophic bacteria get their nutrients from carbon-containing organic chemicals found in other living organisms.
Methanogenesis: a metabolism unique to Archaea, which produces methane gas as a by-product.
Methanogenesis occurs in environments lacking oxygen.
Methane-producing archaea live in the digestive tracts of animals, such as cattle.
Some bacteria are photosynthetic, best known as cyanobacteria.
These bacteria are abundant in both fresh and saltwater and account for much of the atmospheric oxygen on Earth.

All animals and plants are Obligate Aerobes: they need oxygen, obtained through cellular respiration, in order to get energy (ATP) from food.
Some bacteria are Facultative Anaerobes, performing cellular respiration in the presence of oxygen and anaerobic respiration when oxygen is low/absent (Fermentation - ATP when oxygen is not present).
Still other bacteria are Obligate Anaerobes: They cannot live in environments where oxygen is present.

Bacteria and Archaea are very diverse in how they obtain nutrients, enabling them to occupy a diverse array of habitats/environments.
Both Bacteria and Archaea occupy environments with oxygen (aerobic) and without oxygen (anaerobic).
Methanogenic Archaea are found in depths of landfills, while anaerobic bacteria reside in human guts.
Extremophiles are organisms that thrive under "extreme" conditions. The term frequently refers to prokaryotes and is sometimes used interchangeably with Archaea.
Extremophilic capabilities of prokaryotes have influenced scientists interested in extraterrestrial life.

Prokaryotes reproduce using Binary Fission.
Binary Fission: is the division of one parent cell into two genetically identical daughter cells (Asexual reproduction).
Not much genetic variation due to asexual reproduction therefore Bacteria and Archaea gain new DNA via plasmids.
This may happen when bacteria is infected by a virus or through Conjugation.
Conjugation is when two cells join to exchange genetic information.
Conjugation is considered sexual reproduction because two different cells are sharing genetic information
Bacteria reproduce quickly, and copying errors result in mutations.
Transformation occurs when a cell picks up loose fragments of DNA from its surroundings and uses it.
These DNA fragments may have been released into the environment when other cells died.
If the new DNA came from a different species, the process is called Horizontal Gene Transfer.