Sept 9-08 - Diversity & Bacteria Notes

Sept 9-08 - Diversity & Bacteria Notes - Josh...

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Josh Bovard Biology 111 – Tuesday, September 9 th , 2008 Professor Graham Bell D IVERSITY AND B ACTERIA – T EXTBOOK N OTES Chapter 26 – pp. 560-581 How did the living world begin to diversify? There are three main domains on earth; bacteria , archaea and eukarya These three domains differ in three significant ways: 1. Prokaryotic (bacteria & archaea) lack a cytoskeleton, therefore without the proteins they cannot commit mitosis They divide by their own method, binary fission 2. The DNA of a eukaryotic cell is stored in the nucleus, whereas the DNA of a prokaryotic cell is generally circular and has only one chromosome They also have plasmids 3. Prokaryotic cells do not have any of the membrane-bound structures ( ex. golgi apparatus & mitochondria) that eukaryotes have Prokaryotes will likely contain folds in the plasma membrane that allow for photosynthesis not present in eukaryotes All three domains are products of billions of years of mutation, natural selection and genetic drift, making them well-adapted to today’s environment The common ancestor of all three domains probably lived 2 or 3 billion years ago Where are prokaryotes found? If measured by numbers of individuals, prokaryotes are the most successful creatures on Earth Over 3 x 10 28 bacteria and archaea in the oceans alone Prokaryotes are found in all types of environments on earth (hot, cold; acidic, basic; bottoms of seas, 2km deep crusts, clouds) Some can also live where there is no oxygen and where oxygen is abundant Bacteria generally take on three shapes: Coccus – spherical-shaped Bacillus – rod-shaped Helical forms – like a corkscrew They may gather in chains, clusters, or be singular Some multicellular prokaryotes have been found, but they are most often individuals living together 1
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Josh Bovard Biology 111 – Tuesday, September 9 th , 2008 Professor Graham Bell The shape of archaea is largely unknown because many have not been observed under a microscope When bacteria live in communities, they tend to produce a dense biofilm , which is a layer of gel- like polysaccharide matrix that traps other cells Prokaryotic Keys to Success Features of prokaryotes that have contributed to their success include unique cell surfaces, modes of locomotion, communication, nutrition and reproduction Cell Wall Almost all bacteria have a cell wall made of peptidoglycan – a polymer of amino sugars –, while almost all archaeal cell wells are made of significant amounts of protein The different composition of the cell walls is a major difference between the two prokaryotic domains Bacteria cell walls can be differentiated with the help of a gram stain Gram-negative (pink to red) results mean cells have only a thin layer of peptidoglycan under an outer membrane (which has a similar composition to the plasma membrane)
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