Archaea
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Contents:
1. Intro
2. Diagnostic Characteristics
3. Habitats
4.Major types
5.Basic anatomy
6.Transport of materials
7.Reproduction
8. Environmental Adaptations


Intro:

Two archaea walk into a bar and the bartender says, "If you guys are going to start in with the jokes again, Woese is me."
In case you don't catch this joke, Carl Woese was the person who first recognized the distinction of archaea and bacteria, and he proposed a six kingdom system. Woese put prokaryotic organisms by comparing their nucleic acid sequences. Organisms in the archaea group are single-celled microorganisms and are prokaryotes, meaning that they lack a nucleus.. Archaea can be then broken down into 3 groups based on environmental criteria: methanogens, extreme halophiles, and extreme thermophiles.


Diagnostic characteristics of the group

Archaea are one of the three domains of life: Bacteria, Archaea, and Eukarya. By comparing ribosomal RNA and the completely sequenced genomes of some species, researchers identified two main branches of prokaryote evolution: bacteria and archaea. Archaea differ from bacteria in many key structural, biochemical, and physiological characteristics.A characteristic such as chromosome form,is similar to Bacteria and Archaea,while the presence of histones is similar between Archaea and Eukarya.(13DO) .Archae can be from 0.1 micrometers up to 15 micrometersand are most commonly found as plates, spheres, rods, or spirals. (EK15)

Characteristic:
Bacteria
Archaea
Membrane Lipids
unbranched hydocarbons
some branched
hydrocarbons

RNA polymerase
one kind
several kinds
Initiator amino acid for start of protein synthesis
formylmethionine
methionine
Introns (noncoding parts of genes)
rare
present in some
genes

Histones associated with DNA
absent
present
Circular Chromosome
present
present
Ability to grow at temp. >100 degrees Celcius
no
some species
Contains peptidoglycan/meurin (prevents osmotic lysis--cell bursting in hypotonic environments) in cell walls (EG 3)
present in almost all
always absent

Size-wise, archaeans range from 0.1 µm to over 15 µm in diameter. They come in a variety of shapes, including spheres, rods, spirals, plates, and even cubes. (SW 2)

This shows the relationship between Archaea and other life forms (T2)
This shows the relationship between Archaea and other life forms (T2)

Habitats

Many species of archaea live in extreme environments where no other life can. These organisms are referred to be extremophiles, "lovers" of extreme environments. They thrive in habitat that may be extremely hot (hot springs and volcanoes), extremely cold (arctic areas), or extremely high or low pH levels. These habitats are detrimental to the majority of life on Earth. Because of this, organisms in the archaea group establish an ecological niche in certain habitats. Other archaea are known as mesophiles, "lovers" of moderate environments (16 HL), and inhabit such environments as marshlands, sewage, and soil (1 MB). Archaeans are not restricted to extreme environements, in fact, new research has shown that they live quite abundantly in the plankton of the marine biomes (9 JSun). Because they thrive in extreme environments, Archaea were originally thought to be bacteria that could survive at extremely high temperatures and were not "discovered" until the 1970s, when they were recognized as genetically different from bacteria (CS 3).

Major types

There are two major types of archaea: Euyarchaeota and Crenarchaeota. Crenarchaeota are characterized by their ability to tolerate extremes in temperature and acidity and the Euyarchaeota include methane-producers and salt-lovers. (6 VK) All the methanogens and halophiles are Euryarchaeota (the word "eury" means "broad", a reference to how broad the variety and habitiat range of these prokaryotes). Some thermophiles are a part of Euryarchaeota, but most of the thermophiles are in the Crenarchaeota group (the word "cren" means "spring", referring to the hydrothermal vents).
Methanogens are among the strictest of anaerobes, meaning that they do anaerobic respiration, respiration without oxygen. Oxygen is poisonous to methanogens. Extreme halophiles live in extremely salty envioments, such as the Dead Sea. Colonies of halophiles form a purple-red scum that is pigmented that way by the use of bateriorhodopsin, a photosynthetic pigment. The next group is extreme thermophiles. These archaea organisms thrive in hot environments. The optimal temperature for these organisms is around 60 to 80 Celsius. A common example of a thermophile is Sulfolobus, which lives in the hot sulfur springs in Yellowstone National Park.

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a hot spring in Yellowstone National Park

Basic Anatomy

Archaea have a very different anatomy compared to bacteria and eukarya. Archaea don't have nuclear envelopes and membrane enclosed organelles like eukarya. Archaea do not have peptidoglycan in the cell wall like bacteria. Archaea are more similar to bacteria than eukarya. In both bacteria and archaea, an example of their similarity is that DNA exists as plasmids, a small ring of DNA, since there is no nucleus in archaea/bacteria. Also, archaea may or may not have flagella; it depends on the species. A large part of what makes Arachea unique from the domain Eukarya and domain Bacteria is in its formation of the cell membrane. There are four distinct differences, which are 1.) the glycerol phospholipids (archae contain L-glycerol instead of D-glycerol) in the cell wall are not mirror images of each other, 2.) side chains are bound with ether compounds instead of ester compounds, 3.) fatty acids do not build the side chains; they are replaced by carbon atoms, and 4.) side chains branch out instead of lying flat. (3 AN)
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Transport of materials

Types of Endocytosis (21 AL)
Types of Endocytosis (21 AL)
Unfortunately, archaea are prokaryotic cells and lack interior membranes and organelles that would aid in the transport of materials. Therefore, transport of materials is mainly done passively, which means that no work (ATP) is needed. All the materials that the organism needs are in its surroundings. Also, specific proteins aid in transporting, as well as endocytosis. Archaea tend to form colonies with one another, and are very dependent on their surroundings. By working in a colony, the transportation of materials becomes easier.

Reproduction

Archaea reproduce asexually by binary fission. Binary fission is "a type of cell division by which prokaryotes reproduce, in which dividing daughter cell receives a copy of the single parental chromosome".Archaea do not do mitosis nor meiosis. Also, multiple fission, budding, and fragmentation may occur since archaea reproduce asexually. Cell division happens in a cell cycle; when the cell's chromosome is replicated and the daughter chromosomes are separated, the cell divides. (3DC)To prokaryotes, the word "grow" means the increase of the number of cells instead of enlargement of individual cells. Archaea have three mechanisms that transfer genes: transformation, which is prokaryotes picking up genes from the surrounding environment, conjugation, which is the direct transfer of genes between prokaryotes, and transduction, which is viruses transferring genes between prokaryotes. Mutation is a crucial key for genetic variation. Without mutation, archaea populations wont be able to adapt to environmental changes and natural selection will not occur.


Environmental Adaptations

Archaea are found in very extreme conditions. to name a few, they live in extreme hot, cold, acidic/basic habitat. Some extreme conditions include the following: some live near rift vents in the deep sea at temperatures well over 100 degrees Centigrade, others live in hot springs or in extremely alkaline or acid waters. They have even been found living inside the digestive tracts of cows, termites, and marine life where they produce methane. (2 AW) At the beginning of their existence, Archaea lived on Earth when it was full of ammonia and methane, yet they thrived in this environment. Archaea may be the only remaining thriving community that dominated the Earth at the very beginning. (EK) Different groups of archaea adapted to live in different environments. In order to flourish in these enviroments, archaea do taxis movement, movement toward or away from a stimulus. Methanogens live in swamps and marshes where there is little to no oxygen because oxygen is poisonous to methanogens. Extreme halophiles live in extremely salty places. The halophiles maintain osmotic balance by building up solutes within their cells in order to not be subjected to lysis. (AS 14) And extreme thermophiles live in hot environments, such as hot springs. Some archaea organisms live in marine environments, such as deep-sea vents. These organisms adapted to live in these harsh enviroments, and mutation greatly helped archaea to adapt.

An interesting application of the extreme thermophile capabilities of archaeans is found in the PCR reaction, a process commonly used in the studies of microbiology and immunology. During a PCR reaction, polymerase chain reaction, a targeted or desired DNA sequence is amplified. First the DNA helix is heated causing the two strands to separate, followed by binding of a primer, then synthesis of a complimentary sequence by the enzyme called taq polymerase. This enzyme was discovered in an archaean called Thermus aquaticus, which was found in hot springs at Yellowstone park. The heat resistant properties of the taq polyemerase allowed it to withstand the heat needed to separate the DNA strands without being denatured. (5 KA).

Review Questions:
1) Which type of archaea is associated with purple-red scum in bodies of water and how is this caused? (J. Stein)
3) How do Archaea increase genetic diversity? (DPOD 4)
4) Describe the unusual habitats of extreme thermophiles and halophiles and how these organisms are adapted to these conditions. (AR 6)
5) Why is mutation so important in Archaea bacteria reproduction? (CH)
6) What evidence indicates that Archea are more closely related to Eukaryotes than to Bacteria? (20RM)
7) How does the structure of Archaea enable them to live in diverse habitats? (JE)

Sources:
Campbell, Neil A, and Jane B. Reece. Biology. Sixth Edition. San Fransisco: Pearson Education, Inc, 2002.
"Morphology of the Archaea." UCMP - University of California Museum of Paleontology. 24 Oct. 2009 <http://www.ucmp.berkeley.ed

[1] "Habitats." 21 Oct. 2009 http://www.spiritus-temporis.com/archaea/habitats.html
[2] "Introduction to Archaea." UCMP - University of California Museum of Paleontology. 24 Oct. 2009 <http://www.ucmp.berkeley.edu/archaea/archaea.html>.
[3] http://student.ccbcmd.edu/courses/bio141/lecguide/unit1/prostruct/cw.html
[4] "Archaea." Wikipedia.org. Wikipedia, the free encyclopedia. Web. 25 Oct. 2009. <http://en.wikipedia.org/wiki/Archaea>.
[5] "Introduction to the Archaea." UCMP-University of California Museum of Paleontology. 25 Oct. 2009 <http://www.ucmp.berkeley.edu/archaea/archaea.html>
[6] "Water Industry." Archaea 25 Oct. 2009 http://waterindustry.org/Water-Facts/archaea-1.htm.
[7] "Archaea." Kimball's Biology Pages. Ed. John W. Kimball. John W. Kimball, 16 Dec. 2008. Web. 1 Nov. 2009. <http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/Archaea.html>.
[8] "Taq Enzyme." World of Microbiology and Immunology. The Gale Group Inc. 2003. Encyclopedia.com. 1 Nov. 2009 <http://www.encyclopedia.com>.
[9] http://www.ucmp.berkeley.edu/archaea/archaea.html