MICROBIO 3101st Edition Lecture 6Outline of Last Lecture I. 2.5 Elements of Microbial StructureII. 2.6 Arrangement of DNA in Microbial CellsIII. 2.7 The Evolutionary Tree of LifeIV. 2.8 Metabolic Diversity V. 2.9 Bacteria VI. 2.10 Archaea VII. 2.11 Phylogenetic Analyses of Natural Microbial Communities VIII. 2.12 Microbial EukaryaOutline of Current Lecture I. 3.1 Cell MorphologyII. 3.2 Cell Size and the Significance of SmallnessIII. 3.3 The Cytoplasmic MembraneIV. 3.4 Functions of the Cytoplasmic MembraneV. 3.6 The Cell Wall of Bacteria: PeptidoglycanVI. 3.7 The Outer MembraneThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.VII. 3.8 Cell Walls of ArchaeaVIII. 3.9 Cell Surface StructuresIX. 3.10 Cell InclusionsX. 3.11 Gas VesiclesXI. 3.12 EndosporesXII. 3.13 Flagella and MotilityXIII. 3.15 Microbial TaxesCurrent Lecture3.1 Cell Morphology• Morphology = cell shape• Major cell morphologies– Coccus (pl. cocci): spherical or ovoid – Rod: cylindrical shape– Spirillum: spiral shape• Cells with unusual shapes– Spirochetes: long, slender, tightly coiled– Appendaged bacteria: appendaged with extension of cell wall– Filamentous bacteria: look like a filament• Many variations on basic morphological types• Morphology typically does not predict physiology, ecology, phylogeny, etc. of a prokaryotic cell• Selective forces may be involved in setting the morphology:– Optimization for nutrient uptake (small cells and those with high surface-to-volume ratio)– Swimming motility in viscous environments or near surfaces (helical or spiral-shaped cells)– Gliding motility (filamentous bacteria)3.2 Cell Size and the Significance of Smallness• Surface-to-Volume Ratios, Growth Rates, and Evolution– Advantages to being small:- Small cells have more surface area relative to cell volume than large cells (i.e., higher S/V)- Support greater nutrient exchange per unit cell volume- Tend to grow faster than larger cells3.3 Cytoplasmic membrane:– Thin structure that surrounds the cell– 6–8 nm thick– Vital barrier that separates cytoplasm from environment– Highly selective permeable barrier; enables concentration– Embedded proteins– Stabilized by hydrogen bonds and hydrophobic interactions– Mg2+ and Ca2+ help stabilize membrane by forming ionic bonds with negative charges on the phospholipids– Somewhat fluid– Can exist in many different chemical forms as a result of variation in the groups attached to the glycerol backbone– Fatty acids point inward to form hydrophobic environment; hydrophilic portions remain exposed to external environment or the cytoplasm• Membrane Proteins– Outer surface of cytoplasmic membrane can interact with a variety of proteins that bind substrates or process large molecules for transport– Inner surface of cytoplasmic membrane interacts with proteins involved in energy-yielding reactions and other important cellular functions– Integral membrane proteins• Firmly embedded in the membrane– Peripheral membrane proteins• One portion anchored in the membrane• Membrane-Strengthening Agents– Sterols• Rigid, planar lipids found in eukaryotic membranes- Strengthen and stabilize membranes – Hopanoids• Structurally similar to sterols• Present in membranes of many Bacteria- Archaeal Membranes– Ether linkages in phospholipids of Archaea– Bacteria and Eukarya that have ester linkages in phospholipids– Archaeal lipids lack fatty acids, have isoprenes instead– Major lipids are glycerol diethers and tetraethers– Can exist as lipid monolayers, bilayers, or mixture 3.4 Function • Permeability Barrier: Polar and charged molecules must be transported – Transport proteins accumulate solutes against the concentration gradient • Protein Anchor– Holds transport proteins in place • Energy Conservation – Site of generation and use of proton motive force3.6 The Cell Wall of Bacteria: Peptidoglycan- Peptidoglycan – Rigid layer that provides strength to cell wall– Polysaccharide composed of:• N-acetylglucosamine and N-acetylmuramic acid• Amino acids• Lysine or diaminopimelic acid (DAP)• Cross-linked differently in gram-negative bacteria and gram-positive bacteria• Gram-Positive Cell Walls – Can contain up to 90% peptidoglycan– Common to have teichoic acids (acidic substances) embedded in the cell wall• Lipoteichoic acids: teichoic acids covalently bound to membrane lipids• Prokaryotes That Lack Cell Walls– Mycoplasmas (associated with TB and Leprosy)• Group of pathogenic bacteria– Thermoplasma• Species of Archaea3.7 The Outer Membrane• Total cell wall contains ~10% peptidoglycan • Most of cell wall composed of outer membrane (aka lipopolysaccharide [LPS] layer)– LPS consists of core polysaccharide and O-polysaccharide– LPS replaces most of phospholipids in outer half of outer membrane– Endotoxin: the toxic component of LPS- Porins: channels for movement of hydrophilic low-molecular weight substances - Periplasm: space located between cytoplasmic and outer membranes – ~15 nm wide– Contents have gel-like consistency – Houses many proteins 3.8 Cell Walls of Archaea • No peptidoglycan • Typically no outer membrane – Reasons why they are extremophiles• Pseudomurein– Polysaccharide similar to peptidoglycan – Composed of N-acetylglucosamine and N- acetyltalosaminuronic acid – Found in cell walls of certain methanogenicArchaea• Cell walls of some Archaea lack pseudomurein• S-Layers– Most common cell wall type among Archaea – Consist of protein or glycoprotein– Paracrystalline structure3.9 Cell Surface Structures • Capsules and Slime Layers– Polysaccharide layers • May be thick or thin, rigid or flexible – Assist in attachment to surfaces (found on our teeth)– Protect against phagocytosis– Resist desiccation (resist drying out)• Fimbriae– Filamentous protein structures-shorter than flagella– Enable organisms to stick to surfaces or form pellicles (hooks)• Pili– Filamentous protein structures – Typically longer than fimbriae– Assist in surface attachment– Facilitate genetic exchange between cells (conjugation)o Two bacteria connect to each other by a pilus and exchange DNA/– Type IV pili involved in twitching motility3.10 Cell Inclusions (storage lockers, energy reserves)• Carbon storage