Diversity of Prokaryotes and Viruses Chapter 19 The good the bad and the ugly Outline Which organisms are members of the Bacteria and Archaea Domains How do Prokaryotes survive and reproduce How do Prokaryotes affect us and other organisms Viruses Viroids and Prions what are they Interesting facts Did you know that you are home to trillions of prokaryotes In terms of abundance prokaryotes rule as Earth s predominant form of life Life on Earth was solely prokaryotic for the first 1 5 billion years The prokaryotic domains Bacteria and Archaea were the first organisms and arose on earth about 3 5 billion years ago While only about 5000 prokaryotic species have been described there may be as many 500 000 5 000 000 Prokaryotes range in size from 0 2 1 0 micrometers in diameter see fig 19 10 How big or small is a micrometer 1 1 000 000 of a meter But just how small is that The thickness of a dime is about 1 millimeter 1000 micrometers The two domains appear similar in many respects however they are different in some very basic ways One main distinction between the Bacteria and the Archaea is that the cell walls of Bacteria contain peptidoglycan Archaea do not This bacterial cell wall is composed of peptidoglycan Peptidoglycan is a complex of structural polysaccharides cross linked by peptides How to identify clades of prokaryotes Shape Locomotion Pigments The cell wall of a bacteria gives it the different types of characteristic shapes See fig 19 1 Nutrients required Staining properties Round cocus Bacillus rod shaped Spirilim spirals The peptidoglycan cell wall of bacteria can be stained by a specific stain known as a Gram stain named for Hans Christian Gram a Danish physician The Domain Bacteria can be divided into two groups based on the ability to be stained with Gram stain Gram positive bacteria have the cell wall exposed to the environment Some bacteria are not stained by Gram stain Gram negative bacteria These bacteria still have a peptidoglycan cell wall but they also have an extra outer membrane Compared with gram positive bacteria gram negative bacteria are more resistant against antibiotics despite their thinner peptidoglycan layer because of their additional relatively impermeable cell wall About half the bacterial species are capable of motion using rotating flagella See 19 2a flagella singular flagellum are filaments that extend from the membrane of a cell and are used for cellular locomotion The anchor of the bacterial flagellum is an axle and wheel arrangement which allows the flagellum to rotate like a propellor Prokaryotes with flagella exhibit either very little movement or random movement when in a uniform environment However in a heterogeneous environment mobile bacteria demonstrate a behavior known as taxis taxis is the orientation or movement of an organism either toward or away from a stimulus If its toward the stimulus positive taxis If its away from the stimulus negative taxis 3 main types of taxis in prokaryotes Chemotaxis movement toward food or away from toxic substance a chemical stimulus Phototaxis movement toward or away from light Magnetotaxis movement toward or away from the Earth s magnetic field All require that the organism have the ability to the sense the stimulus The sensors are usually in the cell membrane A slime layer surrounds the cell walls of some prokaryotes and functions to attach the prokaryote to a surface and may also act as protective covering see fig 19 3 Slime layer is made up of polysaccharide or protein Sometimes these bacteria aggregate to form biofilms This biofilm is dental plaque the cause of tooth decay Another way that bacteria attach themselves to a surface e g a host cell or another bacterium via pili singular pilus pili are hair like structures on the surface of certain bacteria that aid in attachment Some prokaryotes especially the bacilli can form a protective endospore in response to harsh environmental conditions endospores are protective resting structures in which the bacterial chromosome is surrounded by a durable wall See fig 19 4 Prokaryotes have evolved to live in almost every possible environment condition found on Earth including some very extreme conditions While the range of conditions that the domains bacteria and archaea can live in is large the conditions a single species requires may be very specific Prokaryotes occupy many diverse habitats however some of the most extreme environments are the realms of the Archaea Some examples include Halophiles salt loving that inhabit the extremely salty Dead Sea and Great Salt Lake Thermophiles heat loving including thermoacidophiles which live in acidic hot springs or in the hot 105o C water surrounding deep sea volcanic vents Yellowstone National Park s hot springs Other autotrophic prokaryotics like cyanobacteria obtain their energy from sunlight via photosynthesis see fig 19 6 There are also heterotrophic prokaryotes that must have an organic food source for either their energy or their carbon source Chemosynthesis some prokaryotes grow using their autotrophic methods and derive their energy form inorganic chemicals This may occur in the presence of oxygen aerobic or without oxygen anaerobic Reproduction in prokaryotes is asexual in the form of binary fission See fig 19 7 http www youtube com watch v DY9DNWcqxI4 ON TEST The entire bacterial chromosome is replicated and passed on to each daughter cell Some prokaryote are able to transfer genetic information between cells by conjugation conjugation is the transfer of genetic information a plasmid between two prokaryotes via a special sex pilus See fig 19 8 Plasmid is a small double stranded ring of DNA that carries extrachromosomal genes in some prokayotes Many eukaryotes form a symbiotic relationship with prokaryotes and relay on each other for an exchange some commodity see fig 19 9 Most bacteria are harmless or even beneficial to humans however some are pathogenic Some diseases caused by pathogenic bacteria are Gonorrhea cholera Syphilis Bubonic plague Tuberculosis Lyme disease Because of the widespread use and misuse of antibiotics some pathogenic bacteria have developed antibiotic resistance There are groups of biological entities that are even smaller than prokaryotes These groups are VIRUSES VIROIDS AND PRIONS some are things that can make organisms sick these are not organisms because they don t have all the requirements for being alive They are however derived from organisms Viruses These particles all
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