State University of New York at BuffaloSchool of Medicine and Biomedical SciencesDepartment of Microbiology and ImmunologyMicrobiology 301D. DombroskiJanuary 20, 2012 829-2355Structure and Function of BacteriaMicrobiology: study of organisms too small to be seen with the unaided eye Microorganism/Microbe/Germ/BugTypes of Microorganisms1. Bacteria2. Fungi3. Parasites4. VirusesBasic cell types1. Prokaryotic2. EukaryoticStructural Organization of Prokaryotic CellA. Appendages 1. flagella (flagellum)2. fimbriae or common pili (pilus)3. sex pilusB. Cell envelope1. glycocalyx (slime layers, capsules)2. cell wall3. cell membrane1C. Cytoplasm1. cell pool2. nucleoid (chromatin body): chromosome3. plasmids4. ribosomes5. inclusion bodies/granulesD. EndosporesGeneral Bacterial StructureA. Appendages: Structures for motility and attachment Flagella: - long hair-like appendages composed of multiple units of the protein flagellin- vary number and arrangement- function – directed movement influenced by positive and negative chemotaxisFimbriae or common pili:- fine bristle-like fibers that are shorter and thinner than flagella- composed of multiple units of the protein pilin. The terminal unit has the ability to stick to substances on surfaces and enable the bacterium to adhere (therefore termed an adhesin)2Sex pilus (specialized pilus)- elongate, rigid, hollow tubular structure through which DNA (plasmid or chromosome) may be transferred (bacterial conjugation)B. Cell Envelope: Outer wrapping of bacteria- viscous (sticky) gelatinous layer around some but not all bacteria- composed of a polysaccharide/protein mix – variable thickness- function1. protection – extreme environmental conditions, loss of water and nutrients2. attachmentTwo types of cell envelopes- slime layer – loose soluble shield non-uniform in density or thickness that protects cell from dehydration and nutrient loss- capsule – thick gelatinous polymer firmly attached to cell wall that contributes to bacterial virulence by protecting bacteria from phagocytosis and destruction by certain white blood cellsCell wall (Exoskeleton of cell)- rigid, net-like matrix of great strength that covers the entire cell and maintains the cell shape- protects cell from osmotic lysis by confining the cytoplasmic membrane- thickness depends on cell type, Gram positive or Gram negative. The Gram stain is a differential staining procedure which detects different physical differences in the cell wall composition- primary component of cell wall is the heteropolymer peptidoglycana. long polysaccharide chains of two repeating disaccharides (glycan chains)1. N-acetylglucosamine (NAG)2. N-acetylmuramic acid (NAM)b. glycan chains are cross-linked (bridged) by short tetrapeptide between M subunitsKey Features of the Gram positive cell wall- multiple layers of peptidoglycan- acidic polysaccharides1. teichoic acid2. lipoteichoic acid- function of teichoic and lipoteichoic acid1. assist in the transport of ions2. reinforce cross linking between glycan chains3Diagram of Gram positive cell wall showing multiple layers of peptidoglycan and cross-connecting side chains of amino acidsKey features of the Gram negative cell wallThree layered cell wallA. Outer membrane – largest part of the multilayered wall1. external to peptidoglycan layer2. semipermeable3. typical phospholipid bilayer4. contains specialized proteinsa. lipopolysaccharidesb. lipoproteinsc. porin proteins – protein channelsB. Periplasmic space1. narrow gap between the inner and outer membrane2. contains degradative or hydrolytic enzymes – phosphates, nucleases, proteases and lipases4lipoteichoicC. Peptidoglycan – one layer thickDiagram of Gram negative cell wallCell membrane (Cytoplasmic membrane, protoplasmic membrane, and inner membrane)- very thin flexible structure lying inside the cell wall, and molded completely around the cytoplasm- phospholipid bilayer containing specialized proteins (peripheral and integral)1. phospholipid molecule consists of three units polar head – phosphate group (hydrophilic) non-polar tails – two long chain fatty acids (hydrophobic)- cell membrane retains cytoplasm and is a selectively permeable barrier- site of metabolic activities attributable to organelles in eukaryote1. respiration and photosynthesis2. transport systems 3. synthesis of cell wall components 54. synthesis of lipids5. secretion of exoenzymes6. secretion of toxinsDiagram of cell membrane showing phospholipid bilayerwith associated proteinsCytoplasm (Protoplasm) and the internal contentsA. Cytoplasm – internal matrix of the cell contained inside the cell membrane- cytoplasm is a dense gelatinous solution with the primary component being water- cell pool – complex mix of nutrients (carbohydrates, amino acids, fatty acids and inorganic ions)- components of cell pool – building blocks for cell synthesis (metabolism) or sources of energy (catabolism)B. Nucleoid (chromatin) – single circle of double stranded deoxyribonucleic acid (DNA) with specialized proteins- contains genetic information for cell structure and function- not enclosed by a membrane6C. Plasmids – circular extrachromosomal strands of DNA found in most bacteria, but not all. They can encode a variety of protective traits or selective advantages:a. antibiotic resistanceb. production of toxinsc. production of enzymesD. Ribosomes – granules of RNA and proteins that function as sites for protein synthesis. Ribosomes resemble those of animal cells but their composition is different. Bacterial ribosomes sediment at 70S; composed of two subunits 50S and 30SE. Inclusion bodies/granules – amorphous particles floating in the cytoplasm and are composed of reserve nutrients stored during periods of abundance. They may contain polysaccharides (glycogen or starch) lipids (polymer of β-hydroxy-butyric acid; PHB) or poly-phosphate (inorganic phosphate)F. Endospores (spores) – mechanism of survival- specialized dormant structure that is synthesized in the cytoplasm of certain Gram positive bacteria *(genus Bacillus and Clostridium), never by Gram negative bacteria- Initiator of spore fermentation is unfavorable growth conditions (lack of nutrients)one bacterial cell one spore- dormant structure with no metabolic activity and no cell division- very resistant to