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Unformatted text preview: Biology 172
Lecture 34: Microbiology April 7, 2008
1. Diversification of Bacteria/Archaea
• Morphological • Metabolic Amazing Facts about Microbes (Bacteria & Archaea) • More than 5,000 species described but likely that tens of millions exist • Number of bacteria that live in and on you vastly outnumbers the total cells in your body • Dominant life form on earth may be a species of bacterial plankton (at surface of sea water) • Found everywhere, in extreme habitats Announcements
Discussion this week: HIV 2. Endosymbiotic T heory 3. Viruses
• Morphology • Viral genomes • Lytic and L ysogenic R eplication Antibiotics (should) kill bacteria
• Many are naturally occurring compounds from fungi and bacteria (e.g. p enicillin) • Antibiotics poison bacterial enzymes involved in cell wall synthesis or ribosomal enzymes (unique prokaryotic metabolic pathways) What is the most likely molecular mechanism responsible for the spread of antibiotic resistant strains? A) Mutation B) Lateral gene transfer C) Meiotic recombination Antibiotic resistance: a growing problem Two major groups of bacteria are distinguished by their outer coverings • Gram-positive cells stain purple with Gram stain; Gram-negative cells are pink; important in pathology lab for identification • Special secretion and transport mechanisms needed to build a plasma membrane on the o utside of the peptidoglycan cell wall 1 Metabolic Diversity: Energy Source and Carbon Source 1. Phototrophs (cyanobacteria) – use light energy to produce ATP by p hotophosphorylation (O2 is electron acceptor) and fix CO2 by the Calvin cycle; others split H2 S instead of water for photosynthesis 2. Organotrophs – oxidize organic molecules with high potential energy to produce ATP by cellular respiration or fermentation; some fix CO2 by other pathways 3. Lithotrophs – oxidize inorganic molecules such as ammonia or methane to produce ATP by cellular respiration; some fix CO2 others use methanol or CO as a carbon source Diversity of Cellular Respiration in Microbes How do euks get nitrogen for synthesizing proteins and nucleic acids?
• Nitrogen cycle requires proks • N2 “fixation” is reduction of molecular nitrogen to form amino groups, ammonia and nitrates used by euks “Cannibalism” is the evolutionary origin of eukaryotic organelles
• Mitochondria originated from p hagocytosis of bacteria with aerobic cellular respiration • Chloroplasts arose from p hagocytosis of cyanobacteria • Explains the presence of circular DNA in these organelles and other structural/chemical characteristics Viruses are parasites that are everywhere
Sea water treated with a fluorescent stain for nucleic acids Viruses are very small and vary in shape • Viruses are not organisms -- they are particles or agents; they are o bligate parasites • Viruses have a genome (RNA or DNA) and they evolve • Viruses enter a host cell and take over its biosynthetic machinery 2 Two Examples: Adenovirus and HIV Viral Genomes are DNA or RNA and Double-stranded or Single-stranded • Enclosed in a shell of proteins = capsid • Or enclosed in a capsid plus membranelike envelope (stolen from host cell) Viruses Replicate by Lytic or Lysogenic Cycles, or Both Attenuated viruses are used for gene therapy to carry the normal gene into the target cell. Which type of virus is best suited to this application? A) Lytic viruses B) Lysogenic viruses C) Either lytic or lysogenic viruses HIV infects CD4+ Helper T-cells Glycoproteins on HIV envelope bind to CD4 and a co-receptor on the host cell membrane
gp120 gp41 Co-receptors: CCR5 (on lymphocytes) and CXCR4 (on macrophages)
gp120 & gp41 3 HIV is a retrovirus
• Retroviruses are ssRNA v iruses that produce reverse transcriptase • Reverse transcriptase is a DNA polymerase that makes cDNA from RNA template
Viral RNA plus reverse transcriptase Host cell makes viral proteins
gp120 gp41 ss cDNA Viral proteins including reverse transcriptase, protease, integrase, envelope and core proteins host DNA Host RNA polymerase viral RNA viral particle ds cDNA Lysogenic replication Lytic replication Viruses bud or burst out of the cell = lysis 4 ...
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