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University of Otago
Keith Ireton

PHCY219 – Microbiology Section 2 – Lecture 4 Keith Ireton Lecture 4 – Cell Structure and Function of Prokaryotes Need to learn about bacterial cell structure and function so that we can understand pathogens and normal microflora. Phylogeny Phylogenetics = study of evolutionary relationship (evolutionary tree).  Three branches 1) Bacteria 2) Archaea 3) Eukarya  Prokaryotes vs. eukaryotes: Prokaryotes don’t have nuclei; usually they have a chromosome (circular).  Archaea and bacteria look the same, but they are distantly related. Archaea more closely related to eukarya. Prokaryotes Eukaryotes  Has a nucleus  Has organelles  Lacks nucleus o Ribosomes  Lacks organelles o Golgi  Has cell wall o Endoplasmic Reticulum o Mitochondria  Lacks cell wall A chromosome is present; it is not in a true nucleusMultiple chromosomes are present  DNA replication But it IS ORGANISED.  mRNA is transported out. Compartments are physically separated. Plants  chloroplasts vs. mitochondria in other species. The red stars indicate pathogens. Examples of Proteobacteria gram –ve bacteria = salmonella and E. coli. Example of gram +ve = S. aureus. Examples of Spirochete = syphilis. Staining can differentiate between gram –ve and gram +ve organisms. PHCY219 – Microbiology Section 2 – Lecture 4 Keith Ireton Gram staining process Initially all the cells are stained purple. After alcohol is introduced, only gram +ve cells are stained. Gram –vecells are not stained. At the last stage of this procedure gram –ve cells are pink due to safranin. Gram +ve bacteria have peptidoglycan layer which is thicker than gram –ve. So when crystal violet is present, it’s harder for it to leave again. So stains the gram +ve cells and not the gram –ve cells. Archaea Archaea can be found in extreme places (high salt, low pH, high temperatures etc). They also have metabolisms that are different. For example methanogens, they degrade organic material into methane. Archaea haven’t been found to be pathogenic to us so far. Size and Shape Bacteria can come in different shapes (morphology). Shape Example Coccus Staphylococcus aureus. Rod E. coli Spirillum Helicobacter pylori Spirochete Borrelia burgdorferi Stalks & Hyphae Caulobacter crescentus Filamentous Streptomyces Size – Bacteria range in size. The smallest is Mycoplasma pneuomoniae (0.2 µm). Conversely, the largest is Thiomargarita namibiensis (750 µm). Advantage of being small: surface area:volume ratio stays small  absorbing nutrients and excreting waste becomes more efficient. Surface area is related to square of the radius. PHCY219 – Microbiology Section 2 – Lecture 4 Keith Ireton Cytoplasmic membrane Bacteria – made of phospholipid bilayer.  Glycerol and phosphates found facing outwards  Two fatty acids found facing inwards.  This arrangement has the hydrophobic and hydroph
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