The microbes in the domain Archaea look like bacteria, but are different in a few essential ways. They often live in extreme places, like in the cold deep sea, hot geysers, or acidic volcanoes.
The third domain, Eukarya, differs greatly from the other two. The cells in the species of this domain, therefore, have a nucleus. Eukarya is the only domain that consists of multicellular and visible organisms, like people, animals, plants and trees. Fungi are so diverse, that two different fungi can be as genetically different as a person and a fish. Some archaeal membranes are lipid monolayers instead of bilayers Figure 2.
Figure 2. Archaeal phospholipids differ from those found in Bacteria and Eukarya in two ways. First, they have branched phytanyl sidechains instead of linear ones. Second, an ether bond instead of an ester bond connects the lipid to the glycerol. The cytoplasm of prokaryotic cells has a high concentration of dissolved solutes. Therefore, the osmotic pressure within the cell is relatively high. The cell wall is a protective layer that surrounds some cells and gives them shape and rigidity. It is located outside the cell membrane and prevents osmotic lysis bursting due to increasing volume.
The chemical composition of the cell wall varies between Archaea and Bacteria, and also varies between bacterial species. Bacterial cell walls contain peptidoglycan , composed of polysaccharide chains that are cross-linked by unusual peptides containing both L- and D-amino acids including D-glutamic acid and D-alanine. Proteins normally have only L-amino acids; as a consequence, many of our antibiotics work by mimicking D-amino acids and therefore have specific effects on bacterial cell-wall development.
There are more than different forms of peptidoglycan. S-layer surface layer proteins are also present on the outside of cell walls of both Archaea and Bacteria. Bacteria are divided into two major groups: Gram positive and Gram negative , based on their reaction to Gram staining. Note that all Gram-positive bacteria belong to one phylum; bacteria in the other phyla Proteobacteria, Chlamydias, Spirochetes, Cyanobacteria, and others are Gram-negative.
The Gram staining method is named after its inventor, Danish scientist Hans Christian Gram — The different bacterial responses to the staining procedure are ultimately due to cell wall structure. Gram-positive organisms typically lack the outer membrane found in Gram-negative organisms Figure 3. Up to 90 percent of the cell-wall in Gram-positive bacteria is composed of peptidoglycan, and most of the rest is composed of acidic substances called teichoic acids. Teichoic acids may be covalently linked to lipids in the plasma membrane to form lipoteichoic acids.
Lipoteichoic acids anchor the cell wall to the cell membrane. Gram-negative bacteria have a relatively thin cell wall composed of a few layers of peptidoglycan only 10 percent of the total cell wall , surrounded by an outer envelope containing lipopolysaccharides LPS and lipoproteins.
This outer envelope is sometimes referred to as a second lipid bilayer. The chemistry of this outer envelope is very different, however, from that of the typical lipid bilayer that forms plasma membranes. Bacteria are divided into two major groups: Gram positive and Gram negative. Both groups have a cell wall composed of peptidoglycan: in Gram-positive bacteria, the wall is thick, whereas in Gram-negative bacteria, the wall is thin. In Gram-negative bacteria, the cell wall is surrounded by an outer membrane that contains lipopolysaccharides and lipoproteins.
Porins are proteins in this cell membrane that allow substances to pass through the outer membrane of Gram-negative bacteria. In Gram-positive bacteria, lipoteichoic acid anchors the cell wall to the cell membrane. Figure 3. Archaean cell walls do not have peptidoglycan. There are four different types of archaean cell walls.
One type is composed of pseudopeptidoglycan , which is similar to peptidoglycan in morphology but contains different sugars in the polysaccharide chain. The other three types of cell walls are composed of polysaccharides, glycoproteins, or pure protein. Other differences between Bacteria and Archaea are seen in Table 4.
Note that features related to DNA replication, transcription and translation in Archaea are similar to those seen in eukaryotes. Bacteria and Archaea differ in the lipid composition of their cell membranes and the characteristics of the cell wall. In archaeal membranes, phytanyl units, rather than fatty acids, are linked to glycerol.
Some archaeal membranes are lipid monolayers instead of bilayers. The cell wall is located outside the cell membrane and prevents osmotic lysis. The chemical composition of cell walls varies between species. Bacterial cell walls contain peptidoglycan. Archaean cell walls do not have peptidoglycan, but they may have pseudopeptidoglycan, polysaccharides, glycoproteins, or protein-based cell walls. Bacteria can be divided into two major groups: Gram positive and Gram negative, based on the Gram stain reaction.
Gram-positive organisms have a thick cell wall, together with teichoic acids. Gram-negative organisms have a thin cell wall and an outer envelope containing lipopolysaccharides and lipoproteins. Improve this page Learn More. Skip to main content. Module 4: Prokaryotes. Search for:. Archaea vs. Molecular Biology and Evolution 21 , — Gogarten, J.
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Discovery of the Giant Mimivirus. Volvox, Chlamydomonas, and the Evolution of Multicellularity. Yeast Fermentation and the Making of Beer and Wine.
Dynamic Adaptation of Nutrient Utilization in Humans. Nutrient Utilization in Humans: Metabolism Pathways. An Evolutionary Perspective on Amino Acids. Mitochondria and the Immune Response. Stem Cells in Plants and Animals. Promising Biofuel Resources: Lignocellulose and Algae. The Discovery of Lysosomes and Autophagy. The Mystery of Vitamin C. Koonin, Ph. Citation: Koonin, E. Nature Education 3 9 How do scientists study and classify life-forms? How can we understand the complex evolutionary connections between living organisms?
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