Chapter 3 Microbiology.pdf

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Biology - Biological Sciences
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BSC 3096

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Chapter 3 Microbiology Tuesday, July 02, 2013 12:33 AM 1. Viruses a. Most basic form consists of a protein coat called a capsid and a various number of genes, either RNA or DNA, NOT BOTH i. b. Most animal viruses, some plant viruses, and very few bacterial viruses surround themselves with a lipid-rich envelope i. The envelope is either borrowed from the membrane of the host cell or synthesized in the host cell cytoplasm ii. iii. Usually contains virus specific proteins c. A mature virus outside the host cell is called a virion d. Always require the host cells reproductive machinery e. Unlike living organisms, viruses in their active form are not separated from their external environment by some type of barrier such as a cell wall or membrane f. Viruses can be crystallized without losing the ability to infect g. Infection beings when a virion attaches to a host cell's receptors i. Cell wall lipopolysaccharides and proteins, teichoic acids, flagella, and pili can serve as receptors ii. iii. h. Bacteriophage i. A virus that infects bacteria ii. Usually injects nucleic acid through the tail after viral enzymes have digested a hole in the cell wall i. Most viruses that infect eukaryotes are engulfed by endocytic process j. Lytic infection i. Virus commandeers the cell's reproductive machinery and beings reproducing new viruses ii. Brief period before first fully formed virion appears is called the eclipse period 1) 2) Period from infection to lysis is called the latent period, which encompasses the eclipse period iii. The cell then can either fill with many new viruses until it lyses or bursts, or it may release the new viruses one at a time in a reverse endocytic process iv. A virus following a lytic cycle is called a virulent virus 1) k. Lysogenic infection i. Viral DNA is incorporated into the host genome 1) If the virus is an RNA virus, it uses reverse transcriptase to create DNA than incorporates it into the host cell 2) When the host cell replicates its DNA, the viral DNA is replicated as well 3) A virus following the lysogenic cycle is called a temperate virus ii. A host cell infected with a temperate virus may show no symptoms of infection 1) While the viral DNA remains incorporated into the host DNA, the virus is said to be 1) While the viral DNA remains incorporated into the host DNA, the virus is said to be dormant or latent, and is called a provirus l. Viruses can be classified many ways i. By the type of nucleic acid they possess 1) Unenveloped plus strand RNA a) Responsible for the common cold b) Plus virus indicates that proteins can be directly translated form the RNA 2) Enveloped plus strand RNA a) "retrovirus" 3) Minus strand RNA a) Measles, rabies and the flu b) Minus strand is complement to mRNA and must be transcribed to plus-RNA before being translated 4) dsRNA,s+dsDNA m. Viroids (not to be confused with virions) i. Small rings of naked RNA without capsids ii. ONLY INFECT PLANTS n. Prions i. Naked viral proteins ii. Capable of reproducing themselves 2. Defense Against Viral Infection a. Human body fights viral infection with antibodies b. Spike proteins encoded fro the viral nucleic acids protrude through the envelope i. These proteins bind to receptors in a new host cell causing virus to be infectious ii. It is the spike proteins that human antibodies recognize when fighting an infection iii. Since RNA Pol does not have a proofreading mechanism, changes in the spike proteins are common 1) When this happens, antibodies fail to recognize them c. Vaccines are either injections of antibodies or injections of a non-pathogenic form of the virus that creates antibodies d. Multiple animals can act as carrier populations i. Even if all viral infections of a certain type were eliminated in humans, the virus may continue to thrive in another animal, thus maintaining its ability to reinfect the human population 3. Prokaryotes a. No membrane bound nucleus b. Split into two domains: Archae and Bacteria i. Archae are usually found in extreme environments 1) Cell walls not made from peptidoglycan c. In order to grow, all organisms require the ability to acquire carbon, energy, and electrons i. Carbon 1) Autotrophs - Use CO2 as their sole source of carbon 2) Heterotrophs - Use preformed organic molecules as their source of carbon ii. Energy 1) Phototroph- energy from light 2) Chemotroph - energy from oxidation of organic or inorganic matter a) Prokaryotes can use inorganic matter, not eukaryotes iii. Electrons (hydrogen) 1) Lithotroph - inorganic matter 2) Organotroph - organic atter d. Some bacteria are capable of fixing nitrogen i. Atmospheric nitrogen, N2, is abundant but is useless to plants in this form ii. Nitrogen fixation is the process that concerts N2 to ammonia 1) Most plants still cant use ammonia and must wait for other bacteria to further process the nitrogen in a process called nitrification 2) Nitrification produces nitrates 3) Requires two genera of chemoautorophic prokaryotes e. Chemoautotrophy i. An inefficient mechanism for acquiring energy ii. Require large amounts of substrate 1) This means they have a large environmental impact, which is reflected in processes like 1) This means they have a large environmental impact, which is reflected in processes like nitrification iii. All known chemoautotrophs are prokaryotes 4. Structure of Prokaryotes a. Have a single, circular double stranded molecule of DNA i. Twisted into supercoils ii. Associated with histones in Archae iii. The DNA, RNA and protein complex in prokaryotes forms a structure visible under the light microscope called a nucleoid (aka chromatin body, nuclear region, nuclear body) iv. b. Various shapes i. Cocci (round) bacilli (rod shaped) ii. Spirilla (spiral shaped) - Rigid iii. Spirochetes (spiral shaped) - More flexible and have internal flagellar arrangement c. Bacteria have both DNA and RNA as well as ribosomes d. Bacteria have organelles, such as the ribosome, nucleoid, mesosome, just not complex, membrane bound organelles e. Mesosome - invaginations of the plasma membrane, that may be in the shape of tubules, lamellae, or vesicales i. Appear as bubbles under the light microscope ii. Function unknown f. Inclusion bodies - granules of organic or inorganic matter i. Storage of carbon, phosphate, and other substances 5. Membranes a. Cytosol of nearly all prokaryotes is surrounded by plasma membrane, made of phospholipids i. If enough phospholipids exist, and the solution is subjected to ultrasonic vibrations, liposomes may form b. Liposome - vesicle surrounded and filled by aqueous solution c. Prokaryotic membranes usually do not contain steroids such as cholesterol i. Instead, some bacteria have steroid like molecules called hopanoids d. Leaflets of the bilayer are asymmetrical i. Glycolipids are found on the outer leaflet only e. Proteins are embedded in the membrane as well i. Integral proteins transverse from the inside to outside the cell ii. Peripheral/extrinsic proteins are situated entirely on the surfaces of the membrane 1) Ionically bonded iii. If the proteins contains carbohydrate portions, that are called glycoproteins 1) Carb portion always protrudes toward the outside of the cell iv. If the protein contains lipids, they are called lipoprotein f. Membrane is fluid i. Can move laterally but cannot separate ii. Hopanoids reduce the fluidity of the membrane 6. Membrane transport 6. Membrane transport a. Brownian motion - random movement of molecules b. Chemical concentration gradient - a gradual change in concentration of a compound over a distance c. Natural membranes are semi-permeable to most compounds, but there are degrees of semipermeability i. Two aspects that affect semipermeability: size and polarity 1) Polar molecules that are big generally need help crossing the membrane a) The greater the polarity, the less permeable it is 2) Very large lipid soluble (nonpolar) molecules can move right through the membrane without assistance ii. Sometimes, the charge difference can outweigh the size difference 1) Water is much larger (and
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