Cell CompositionCell ConstructionSlide 3Prokaryote StructureCell MembranesEubacteria vs. ArchaebacteriaArchaea vs bacteria membranesMembrane functionSize and diffusionMembrane function 2Membrane and metabolismH+ gradients across the membraneSlide 13Membrane functions (other)Cell WallSlide 16Slide 17Peptidoglycan layerOuter membrane – Gram (-)External featuresSlide 21Inside the cellCell structureSlide 24NucleoidRibosomesRNA and protein constructionTranscriptionTranslationSlide 30rRNASlide 32Cell Composition•70-90% water•Organic chemistry key to the construction of cells is inherently linked to the properties of water vs. organic compounds•Consider 4 groups of monomers (a single, repeated ‘building block’):–Sugars–Fatty Acids–Nucleotides–Amino AcidsPolysaccharidesLipidsNucleic AcidsProteinsMacromoleculesCell Construction•OK – using the building blocks we have described, let’s make a microbe…FlagellaFunction(s) Swimming movementPredominant chemical composition ProteinPiliSex pilus Mediates DNA transfer during conjugation ProteinCommon pili or fimbriaeAttachment to surfaces; protection against phagotrophic engulfmentProtein Capsules (includes "slime layers" and glycocalyx)Attachment to surfaces; protection against phagocytic engulfment, occasionally killing or digestion; reserve of nutrients or protection against desiccationUsually polysaccharide; occasionally polypeptideCell wallGram-positive bacteriaPrevents osmotic lysis of cell protoplast and confers rigidity and shape on cellsPeptidoglycan (murein) complexed with teichoic acidsGram-negative bacteriaPeptidoglycan prevents osmotic lysis and confers rigidity and shape; outer membrane is permeability barrier; associated LPS and proteins have various functionsPeptidoglycan (murein) surrounded by phospholipid protein-lipopolysaccharide "outer membrane"Plasma membranePermeability barrier; transport of solutes; energy generation; location of numerous enzyme systemsPhospholipid and proteinRibosomes Sites of translation (protein synthesis) RNA and proteinInclusions Often reserves of nutrients; additional specialized functionsHighly variable; carbohydrate, lipid, protein or inorganicChromosome Genetic material of cell DNAPlasmid Extrachromosomal genetic material DNAProkaryote StructureCell wallmembraneNuclear materialMembrane is critical part of how food and waste are transported - Selectively permeablePhospholipid layerTransport proteinsCell Membranes•The membrane separates the internal part of the cell from the external  that these environments remain separate, but under CONTROLLED contact is a key to lifeMembrane Components:•Phospholipid bilayer•Hopanoids, which provide additional structural stability (similar to sterols (cholesterols) which provide rigidity to eukaryote cells)•Proteins – direct transport between outside and inside the cell~ 40% lipid, 60% proteinEubacteria vs. ArchaebacteriaBacterial cell structureArchaeal cell structureDifference??Let’s look more closely at the membrane, though only 8 nm thick, it is the principle difference between these 2 groups of microbesArchaea vs bacteria membranes•Principle difference between these two is the membrane•In archaea, lipids are unique  they have ether linkages instead of ester linkagesMembrane function•SELECTIVELY PERMEABLE–Passive diffusion  Gases (O2, N2, CO2, ethanol, H2O freely diffuse through layer–Osmosis  because solute concentration inside the cell are generally higher (10 mM inside the cell), water activity is lower inside, H2O comes in – increased water results in turgor pressure (~75psi)–Protein-mediated transport  selective and directional transport across the membrane by uniporters and channel proteins, these facilitate diffusion – still following a gradient and does not require an energy expenditure from the cellSize and diffusionMembrane function 2 •Active transport  proteins that function to move solutes against a gradient, this requires energy•Uniport, Symport, and Antiport proteins guide directional transport of ions/molecules across membrane – different versions can be quite selective (single substance or class of substances) as to what they carryMembrane and metabolism•As the membrane is the focus of gradients, this is where electron transport reactions occur which serve to power the cell in different ways•Many enzymes important to metabolic activity are membrane boundH+ gradients across the membrane•Proton Motive Force (PMF) is what drives ATP production in the cell (pH=1.4 =0.14 V =23 KJ/mol)Figure 5.21Membrane functions (other)•In addition to directing ion/molecule transport and providing the locus for energy production, membranes are also involved in:–Phospholipid & protein synthesis for membrane–Nucleoid division in replication–Base for flagella–Waste removal–Endospore formation•Though very small, the membrane is critical to cell function  Lysis involves the rupture of this membrane and spells certain death for the organismCell Wall•Cell wall structure is also chemically quite different between bacteria and archaea•Almost all microbes have a cell wall – mycoplasma bacteria do not•Bacteria have peptidoglycan, archaea use proteins or pseudomurein•The cell wall serves to provide additional rigidity to the cell in order to help withstand the turgor pressure developed through osmosis and define the cell shape as well as being part of the defense mechanisms•Cell wall structure•Two distinct groups of bacteria with very different cell walls–Gram negative has an outer lipid membrane (different from the inner, or plasma membrane) –Gram positive lacks the outer membrane but has a thicker peptidogycan layerPeptidoglycan layer•This layer is responsible for the rigidity of the cell wall, composed of N-Acetylglucosamine (NAG) and N-acetylmuramic (NAM) acids and a small group of amino acids. •Glysine chains held together with peptide bonds between amino acids to form a sheetOuter membrane – Gram (-)•Lipid bilayer ~7 nm thick made of phospholipids, lipopolysaccharides, and proteins•LPS (lipopolysaccharides) can get thick and is generally a part that is specifically toxic (aka an endotoxin)•LPS layers are of potential enviornmental importance as a locus of chelators and electron shuttles•Porins are proteins that are basically soluble to ions and molecules, making the outer layer effectively more porous than the inner membrane, though