Archaea, Bacteria, Viruses, and Protists

Bacteria

• Bacteria are single celled prokaryotes.
• No organelles - only a cell wall, cell membrane, DNA, and enzymes
• Cell wall - not rigid like a plant cells, but flexible and gooey composed of peptidoglycan
• Useful as a signal to other bacteria
• Can protect pathogenic bacteria from host's defenses
• Cell membrane - semipermeable, like all cell membranes
• DNA - single loop of DNA, with numerous plasmids

• enzymes - do all of the work of organelles, all spread out within the cytoplasm
• Not completely true - some internal "compartmentalizaiton" - is this the road to organelles???
• Most diversity is biochemical, not morphological (they are kind of restrained here)

• synthesize their own organic compounds using sunlight as the energy source
• the theory of endosymbiosis states that one of these organisms was taken in by another prokaryote and eventually degenerated to become the chloroplast

Chemoautotrophs - sulfur-loving bacteria

need CO2 as a carbon source obtain energy not from light, but from the oxidization of H2S, HN4, or Fe+

Heterotrophs

obtain their energy from organic compounds made by the photo - and chemoautortrophs

• Bacteria can also can occupy any ecological role
• Producers, consumers, decomposers, predator, prey, etc
• anarobic and aerobic respiration found
• endosymbiosis - the intake of an aerobic prok by another - occurred once
• All eukaryotes have the same genetic and biochemical pathways - leading one to determine that the endosymbiosis occurred once

• Reproduction
• The chromosome is a single, circular strand of DNA
• Additional DNA may be found in circular rings called plasmids
• Plasmids function in antibiotic resistance and conjugation
• Plasmids are also commonly used by genetic engineers to introduce foreign genes into bacteria
• Bacteria reproduce through binary fission

Archaea

The Archaea, once thought to be nothing more than a special type of bacteria, are now known to be a very ancient lineage

• The Archaea have the following unique characteristics:
• plasmid membranes with lipid compositions not seen in any other lifeforms
• RNA polymerase and ribosomes are unique, but more similar to eukaryotes
• Most Archaea live in extreme environments which may be reminiscent of ancient environments
• Methanogens - anaerobes that produce large amounts of methane gas (CH₄)
• important in the carbon cycle
• strict anaerobes - they are poisoned by oxygen
• often used in sewage treatment plants
• Halophiles - "salt-loving" Archaea
• found in such extremely saline locales such as the Dead Sea and the Great Salt Lake
• mostly heterotrophs, but can switch to photosynthesis because of a unique pigment called bacteriorhodopsin

• Thermophiles - "heat-loving" Archaea
• found in hot springs, acidic soils, near volcano vents, etc.
• they use H₂S to generate ATP

Viruses

• Viruses are DNA encased in protein. They are not alive, yet are capable of replication.
• Origin - some have said that they represent the first forms of life, but this is unlikely, since they are basically parasites
• Replication - two stages
• lytic - genetic information is injected into cell
• cell machinery is used to create more viruses
• viruses are released by lysis (cell breakage)
• lysogenic (temperate) - genetic information is injected into cell
• DNA is incorporated into chromosomes
• Numerous replications occur
• cell will enter lytic stage after latent period

• Genetic material - DNA or RNA
• RNA less stable, therefore these types of bacteria have a high mutation rate
• HIV is an RNA virus

Protists

• Wastebasket assemblage of small eukaryotes
• Basically, all of the other three eukaryotes kingdoms (plant, fungi, animals) fit into neat packages - those that didn't were put here

Three main groups of protists:

An amoeba	Foraminifera	Helizoans

Slime molds have two stages in life cycle free living (amoeboid) stage plasmodial ("slug") stage are often brightly colored probably most closely related to sarcodina

Water molds - closely related to true fungi important marine decomposers Phytophthora infestans caused Irish potato famine ich, a fish-gill infestation, is also caused by a water mold

Euglenoids - flagellated, have photoreceptors, photosynthetic, autotrophic

Dinoflagelates - two flagella and a silicon test cause red tides

The next two groups, the Chrysophytes and the Phaeophytes are collectively called the Chromists. They used to be placed in different divisions due to their very different morphologies, but closer inspection of their chloroplast characteristics have indicated that they are very closely related groups.

Chrysophytes - diatoms and their relatives prominent photosynthetic pigment = fucoxanthin Diatom anatomy

Phaeophytes (brown algae) - kelps, Sargasso prominent photosynthetic pigment = fucoxanthin cell walls contain algin, a common food additive used in ice cream, beer, frozen foods, toothpaste, floorwaxes, and paper (among other uses).

Rhodophytes (red algae) - one of the most ancient groups of eukaryotes can live in very deep waters cell walls contain agar, which is used as a moisture-preserving agent in baked goods and jellies

Chlorophytes (green algae) mostly fresh water species possess same pigments identical to land plants - they are their closest relative

All of the plant-like protists have different chloroplasts - therefore they are the end product of a second endosymbiosis between an aerobic (w/ mitochondria) bacteria/proto-eukaryote and a photosynthetic bacteria

Try to find where each of these groups resides on the Tree of Life presented below:

Note - the Sarcodina are called the Entamoebae

the Mastigophora are called the Flagellates

the water molds, euglenoids, dinoflagellates, chrysophya, phaeophyta, and rhodophyta are not listed