![]() The prokaryote, now enlarged, is pinched inward at its equator and the two resulting cells, which are clones, separate. (Recall that the DNA of a prokaryote is a single, circular chromosome.) Prokaryotes do not undergo mitosis instead, the chromosome is replicated and the two resulting copies separate from one another, due to the growth of the cell. Reproduction in prokaryotes is asexual and usually takes place by binary fission. Differences and Similarities between Bacteria and Archaea Note that features related to DNA replication, transcription and translation in Archaea are similar to those seen in eukaryotes. Other differences between Bacteria and Archaea are seen in (Figure). The other three types of cell walls are composed of polysaccharides, glycoproteins, or pure protein. One type is composed of pseudopeptidoglycan, which is similar to peptidoglycan in morphology but contains different sugars in the polysaccharide chain. There are four different types of archaean cell walls. Gram-negative bacteria have a cell wall made of peptidoglycan, whereas Gram-positive bacteria have a cell wall made of lipoteichoic acid.Īrchaean cell walls do not have peptidoglycan.The cell wall of Gram-negative bacteria is thick, and the cell wall of Gram-positive bacteria is thin.Porins allow entry of substances into both Gram-positive and Gram-negative bacteria.Gram-positive bacteria have a single cell wall anchored to the cell membrane by lipoteichoic acid. ![]() Which of the following statements is true? (credit: modification of work by “Franciscosp2″/Wikimedia Commons) ![]() In Gram-positive bacteria, lipoteichoic acid anchors the cell wall to the cell membrane. Porins are proteins in this cell membrane that allow substances to pass through the outer membrane of Gram-negative bacteria. In Gram-negative bacteria, the cell wall is surrounded by an outer membrane that contains lipopolysaccharides and lipoproteins. 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. Bacteria are divided into two major groups: Gram positive and Gram negative. Cell walls in Gram-positive and Gram-negative bacteria. The chemistry of this outer envelope is very different, however, from that of the typical lipid bilayer that forms plasma membranes.įigure 8. This outer envelope is sometimes referred to as a second lipid bilayer. 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. Lipoteichoic acids anchor the cell wall to the cell membrane. Teichoic acids may be covalently linked to lipids in the plasma membrane to form lipoteichoic acids. 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. ![]() Gram-positive organisms typically lack the outer membrane found in Gram-negative organisms ( (Figure)). The different bacterial responses to the staining procedure are ultimately due to cell wall structure. The Gram staining method is named after its inventor, Danish scientist Hans Christian Gram (1853–1938). Note that all Gram-positive bacteria belong to one phylum bacteria in the other phyla (Proteobacteria, Chlamydias, Spirochetes, Cyanobacteria, and others) are Gram-negative. S-layer (surface layer) proteins are also present on the outside of cell walls of both Archaea and Bacteria.īacteria are divided into two major groups: Gram positive and Gram negative, based on their reaction to Gram staining. (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 100 different forms of peptidoglycan. The chemical composition of the cell wall varies between Archaea and Bacteria, and also varies between bacterial species.īacterial 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. It is located outside the cell membrane and prevents osmotic lysis (bursting due to increasing volume). The cell wall is a protective layer that surrounds some cells and gives them shape and rigidity. Therefore, the osmotic pressure within the cell is relatively high. The cytoplasm of prokaryotic cells has a high concentration of dissolved solutes.
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