Chapter 27 - Chapter 27-Prokaryotes Concept 27.1...

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Chapter 27-Prokaryotes 02/03/2008 17:58:00 Concept 27.1 Prokaryotic cells have a variety of shapes. o Three most common are spheres (cocci), rods (bacilli), and spirals o One of the most important features are the prokaryotes cell walls.  The cell wall maintains cell shape, provides physical protection,  and prevents the cell from bursting in a hypotonic environment. o In contrast to prokaryotic cell walls, bacterial cell walls contain  peptidoglycan, a network of modified-sugar polymers cross-linked by  short polypeptides Using a technique called the  Gram stain , scientists can classify many  bacterial species into two groups based on differences in cell wall  composistion.   o Gram-positive  bacteria have simpler walls with a relatively large  amount of peptidoglycan. o Gram-negative  bacteria have less peptidoglycan and are structurally  more complex, with an outer membrane that contains  lipopolysaccharides.   Among pathogenic bacteria (disease-causing), gram-negative  species are generally more threatening than gram-positive  species. The cell wall of many prokaryotes is covered by a 
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Chapter 27 - Chapter 27-Prokaryotes Concept 27.1...

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