Prokaryotes

Prokaryotes are cells without nuclei and other organelles.

Prokaryotes: Eubacteria and Archaea

They're divided into 2 genetic main groups: 

bacteria (formerly eubacteria) and archaea (formerly archaebacteria). 

Most are 1 - 2 μm. 

500-1000 can fit across the letter "i" 's dot. 

They live in all habitat. E.g. surface of other organisms, water and soil deep Earth, and boiling spring. Their total number may exceed all other population. Everything known is based on a tiny fraction of the total species numbers. Only 10k species are identified, just 1% of total species. 

So few have been identified as it's hard to find them in remote places and extreme conditions to grow in a lab.

Harmful prokaryotes

Some prokaryotes are pathogenic to humans, like tuberculosis, strep throat, cholera, typhoid fever.

• pathogenic: disease-causing

Some are pathogenic to livestocks and crops can threaten food supply.

Bacteria existed roughly 3.5 billion years ago, deemed among the oldest organisms, but not as old as the archaea. Many think that archaea and bacteria developed separately from a common ancestor 4 billion years ago that divided into these 2 types. Despite the resemblance bacterias are dissimilar from archaeon.

Bacterial classification

2 ways to classify bacteria are: 

1. 3 types based on their response to gaseous oxygen. 

   1. Aerobic bacteria need oxygen for their health and will die without it. 

   2. Anerobic bacteria can't tolerate gaseous oxygen at all and die when exposed to it. 

   3. Facultative aneraobes can live with and without oxygen.

2. 2 types by how they obtain energy.

   1. Heterotrophs bacteria consume organic compounds, like species found in decaying materials or those using respiration.

   2. Autotrophs bacteria create their own energy, fueled by light or with chemical reaction.

Metabolism

• metabolism: chemical reactions produced inside living being's cells.

Bacteria are very diverse in ways to get nutrients and energy. 

Autotrophic bacteria assemble complex carbon molecules from basic inorganic chemicals, like carbon dioxide, water, and minerals from abiotic environments.

Heterotrophic ones get their nutrients from carbon with organic chemicals found in other livings or their remains.

• inorganic chemicals: a chemical with abiotic origin; simple substances produced by organisms are inorganic 

• organic chemicals: chemical with an abiotic origin; some simple substance produced by organisms are organic

The 2 main energy sources for living beings are sunlight and chemical energy, with the most known being chemical energy inside organic chemicals like sugar and proteins. All animals and plants are obligate aerobes: they need oxygen from respiration process to get energy from food.

Facultive aerobes bacteria perform aerobic respiration in oxygen and anaerobic respiration or anaerobic fermentation, when oxygen is absent.

• obligate aerobes: organisms that can't live without oxygen

• facultative aerobes: organisms that can or can't live without oxygen

• fermentation: an anaerobic process releasing chemical energy from food

Some are obligate anaerobes: they can't live where there's oxygen.

Reproduction

Prokaryotes often reproduce asexually, when a parent cell divides by binary fission, forming 2 daughter cells each, receiving an exact copy of the genetic material from the parent cell; its chromosome and plasmids. At times, errors occur when the genetic material is copied. 

• binary fission: the division of a parent cell into 2 genetically identical daughter cells, a form of asexual reproduction

Copying errors results in mutation or genetic makeup change of the cell.

Since bacteria reproduce faster, they mutate more than slow-reproducing organisms.

They can increase their genetic diversity by gaining DNA, occurring when a bacterium is infected by a virus or through conjugation, when one bacterial cell passes a plasmid copy to a nearby cell through a hollow pilus) and transformation, when cells pick up a loose DNA fragment from its surroundings to use, which may be released from an environment when other cells died.

Bacterial structure

Outside of cell membranes, are cell walls, which are made of peptidoglycan/murein and are different from plant and fungi cell walls, something that only bacteria have. It identifies different bacteria type and is essential for its survival.

Peptidoglycan

Capsule - is the third protective covering that some species have, which is made of polysaccharides (complex carbohydrates). Capsules play many roles. The most important is to keep the bacterium from drying by protecting it from phagocytosis (engulfing) by larger microorganisms. The capsule is a major virulence factor in major disease-causing bacteria, like Escherichia coli and Streptococcus pneumoniae. Nonencapsulated mutants of these organisms are avirulent.

• avirulent: uncapable of causing disease

The cell envelope is made of 2-3 layers: 

1. The interior cytoplasmic membrane

2. the cell wall

3. In some species of bacteria, an outer capsule

When exposed to a gram stain, gram-positive bacteria retain the purple color of the stain because the structure of their cell walls traps the dye. In gram-negative bacteria, the cell wall is thin and releases the dye readily when washed with an alcohol or acetone solution.

Cell Envelope - The cell envelope is made up of two to three layers: the interior cytoplasmic membrane, the cell wall, and - in some species of bacteria -- an outer capsule.

Bacteria aggregation

• aggregation: collection, or the gathering of things together

Prefixes are used with the name of a bacteria's shape to indicate the number of bacteria together.

• pairs (diplo), 

• chains (strepto), 

• clusters (staphylo).

E.g. "diplo" + "coccus" = diplococcus (pair of sphere) or streptobacillus (chain of rods).