Bacterial Structure and Function PDF

Topic 1.3: Bacterial Structure and Function 1  2 Comparing Prokaryotic and Eukaryotic Cells  Prokaryote comes from the Greek words for pre nucleus  Prokaryotes don’t have membrane-bound organelles  Eukaryote comes from the Greek word...

Topic 1.3: Bacterial Structure and Function 1  2 Comparing Prokaryotic and Eukaryotic Cells  Prokaryote comes from the Greek words for pre nucleus  Prokaryotes don’t have membrane-bound organelles  Eukaryote comes from the Greek words for true nucleus  Eukaryotes have a nucleus and membrane-bound organelles, such as the Golgi apparatus, endoplasmic reticulum, and mitochondria  3 Comparing Prokaryotic and Eukaryotic Cells Prokaryote: Eukaryote:  One circular  Paired chromosomes, chromosome, not in a in nuclear membrane membrane  Has histones  No histones  Organelles (specialized  No organelles shape & function)  Bacteria: peptidoglycan  Polysaccharide cell walls, cell walls when present  Archaea: pseudomurein  Divides by mitosis cell walls  Divides by binary fission  4 Basics of Bacterial Cells  Average size: 0.2 to 2.0 μm diameter × 2 to 8 μm in length  Most bacteria are monomorphic (single shape)  A few are pleomorphic (multiple shapes)  5 Shapes of Bacterial Cells  1) Bacillus/rod (rod-shaped)  2) Coccus (spherical-shaped)  3) Spiral  Vibrio – gently curved, like a comma  Spirillum – rigid helix/corkscrew, twisted at least 2, but possibly more than 2 times along its axis (polar external flagella)  Spirochete – similar twists to spirillum, but more flexible, like a spring (inner axial filaments/periplasmic flagella)  6 Shapes of Bacterial Cells – Rods Combination of coccus and bacillus (short and plump). Still a bacillus shape.  7 Shapes of Bacterial Cells – Rods  Scientific genus name: Bacillus  Shape: bacillus  Gram-stained Bacillus anthracis (genus and species)  8 Shapes of Bacterial Cells – Spiral Bacteria Gently curved Vibrio Rigid helix/corkscrew Spirillum Flexible, like a spring Spirochete  9 Arrangements of Bacterial Cells – Cocci  Arrangements = natural groupings of bacteria  Dependent on division patterns/planes and daughter cell attachment locations Cocci can divide along any plane  10 Arrangements of Bacterial Cells – Cocci  Individual/single: a single coccus  Pairs/diplo: diplococci  Clusters/staphylo: staphylococci (think a bunch of grapes)  Chains/strepto: streptococci  Tetrads: groups of four  Sarcinae: cube-like groups of eight  11 Arrangements of Bacterial Cells – Cocci  Pairs/diplo  Chains/strepto  Tetrads  Sarcinae  Clusters/staphylo  12 Arrangements of Bacterial Cells – Cocci Plane of division Diplococci Streptococci Tetrad Sarcinae Staphylococci  13 Arrangements of Bacterial Cells – Rods  Rods/bacilli can only divide along their long axis, so no clusters  Individual/single: a single rod/bacillus  Pairs/diplo: diplobacilli  Chains/strepto: streptobacilli  Palisades: side-by-side rows  14 Arrangements of Bacterial Cells – Rods  15 Structures of a Prokaryotic Cell – Bacteria  16 Structures of a Prokaryotic Cell All cells have these  17 Bacterial Glycocalyx  External to the cell wall  Viscous and gelatinous  Made of polysaccharide and/or polypeptide  Two types:  Capsule: neatly organized and firmly attached. Often larger than the cell itself!  Slime layer: unorganized and loose, easily washed away  18 Bacterial Glycocalyx  Important for bacterial attachment  Contributes to virulence  Capsules prevent phagocytosis (immune cell eating)  Extracellular polymeric substance helps form biofilms  19 Bacterial Capsules: Streptococcus pneumoniae, the Cause of Pneumococcal Pneumonia Capsules  20 Bacterial Flagella  Filamentous appendages external to the cell  Propel bacteria in an aqueous environment – used for motility  Made of protein called flagellin  Three parts:  Filament: whip-like structure at the end of the flagellum  Hook: curved tubular structure that surrounds the base of the filament  Basal body: stack of rings that goes through the cell wall and into the membrane, anchoring the flagellum to the cell  21 Bacterial Flagella Gram Negative Cell Gram Positive Cell 20nm diam. & 1-70μm long  22 Animation: Bacterial Flagellar Structure  23 Bacterial Flagella – Polar Arrangements  Species have varying numbers of flagella in different cellular locations:  Monotrichous (Greek tricho = hair) – one flagellum from one pole  24 Bacterial Flagella – Polar Arrangements  Species have varying numbers of flagella in different cellular locations:  Amphitrichous – one (or >1) flagellum from both poles  25 Bacterial Flagella – Polar Arrangements  Species have varying numbers of flagella in different cellular locations:  Lophotrichous – tufts or bunches of flagella from one or both poles  26 Bacterial Flagella – Non-polar Arrangement  Species have varying numbers of flagella in different cellular locations:  Peritrichous – multiple flagella randomly from all around the cell  27 Animation: Bacterial Flagellar Arrangements  28 Bacterial Flagella  Flagella allow bacteria to move toward or away from stimuli (taxis)…i.e. chemotaxis, phototaxis  Flagella rotate to “run” or “tumble”  29 Animation: Bacterial Motility  30 Bacterial Flagella and Motility  31 Bacterial Flagella and Motility  As a bacterium gets closer to an attractant, the runs become longer between less frequent tumbles  32 Animation: Bacterial Flagellar Movement  33 Bacterial Flagellar Movement  Counterclockwise rotation = run forward  Clockwise rotation = tumble  Positive chemotaxis is movement towards a chemical stimulus/attractant (i.e. a nutrient)  Negative chemotaxis is movement away from a chemical repellant (i.e. toxic compound)  One can visualize cellular movement in a liquid (quick) or semisolid medium  34 Bacterial Axial Filaments  Also called endoflagella because they are internal  Found in spirochetes, in the periplasmic space  Anchored at one end of a cell  Rotation causes cell to move like a corkscrew  35 Animation: Spirochetes  36 Bacterial Axial Filaments Outer membrane  37 Bacterial Fimbriae and Pili  Fimbriae  Hair- or brush- like appendages that allow for attachment  More common than pili  38 Bacterial Fimbriae and Pili  Pili  Involved in motility (gliding and twitching motility)  Conjugation pili involved in DNA transfer from one cell to another  Involved in the “mating” process of bacterial conjugation, in which a donor cell transfers DNA to a recipient cell  39 Bacterial Cell Wall  Prevents osmotic lysis and protects the cell membrane  Made of peptidoglycan (in bacteria)  Contributes to pathogenicity  40 Cell Wall – Composition and Characteristics  Peptidoglycan  Polymer of a repeating disaccharide in rows:  N-acetylglucosamine (NAG)  N-acetylmuramic acid (NAM)  Rows are linked by polypeptides  41 Cell Wall – Composition and Characteristics Tetrapeptide side chain N-acetylglucosamine (NAG) Peptide cross-bridge N-acetylmuramic acid (NAM) Side-chain amino acid Cross-bridge amino acid NAM Peptide bond Carbohydrate "backbone" Structure of peptidoglycan in gram-positive bacteria  42 Gram-Positive vs. Gram-Negative Bacteria Gram (+) Gram (-)  43 Gram-Positive Cell Walls  Thick peptidoglycan layer  One periplasmic space (between cell wall and membrane)  Teichoic acids  Lipoteichoic acid links cell wall to plasma membrane  Wall teichoic acid links the peptidoglycan layers  Carry a negative charge  Regulate movement of cations (positively charged ions)  44 Gram-Positive Cell Walls  45 Gram-Negative Cell Walls  Thin peptidoglycan layer  Outer membrane made of polysaccharides, lipoproteins, and phospholipids  Contains lipopolysaccharides (LPS)  Lipid A is an endotoxin embedded in the top layer  Two periplasmic spaces  Periplasm between the outer membrane and the plasma membrane contains peptidoglycan layer  Porins (proteins) form channels through membrane  46 Gram-Negative Cell Walls  47 Cell Walls and the Gram Stain Mechanism  Crystal violet-iodine crystals form inside cell  Gram-positive  Ethanol or Acid Alcohol dehydrates peptidoglycan  CV-I crystals do not leave, so purple remains  Gram-negative  Ethanol or Acid Alcohol dissolves outer membrane and leaves holes in peptidoglycan  CV-I washes out, so cells are colorless  Safranin added to stain cells  48 Gram-Positive vs. Gram-Negative Staining  49 Plasma (Cytoplasmic) Membrane  Phospholipid bilayer that encloses the cytoplasm  Peripheral proteins on the membrane surface  Integral and transmembrane proteins penetrate the membrane  50 Plasma Membrane Outside Pore Lipid bilayer Peripheral protein Inside Polar head Nonpolar Integral fatty acid proteins tails Peripheral protein Polar head A portion of the inner membrane showing the lipid bilayer and proteins  51 Animation: Plasma Membrane Structure  52 Membrane Structure and Functions  Fluid mosaic model:  Membrane is as viscous as olive oil  Proteins move freely for various functions along the bilayer  Phospholipids rotate and move laterally  Self-sealing  The plasma membrane's selective permeability allows the passage of some molecules, but not others  Contain enzymes for ATP production  ATP is the currency for cellular energy (more about it in the next Unit)  53 Animation: Membrane Permeability  54 Movement of Materials Across Membranes  Passive processes: substances move from high concentration to low concentration  No energy expended  Active processes: substances move from low concentration to high concentration  Energy expended  55 Passive Processes  Simple diffusion: movement of a solute from an area of high concentration to an area of low concentration  The process continues until molecules reach equilibrium  56 Animation: Passive Transport and Principles of Diffusion  57 Passive Processes  Facilitated diffusion: solute combines with a transporter protein in the membrane  Transports ions and larger molecules across a membrane with the concentration gradient  58 Animation: Passive Transport: Special Types of Diffusion  59 Passive Processes  Osmosis: the movement of water across a selectively permeable membrane from an area of higher water concentration to an area of lower water concentration  Through lipid layer  Or through aquaporins (water channels)  60 Passive Processes  61 Passive Processes  Isotonic solution: solute concentrations equal inside and outside of cell  Water is at equilibrium  Hypotonic solution: solute concentration is lower outside than inside the cell  Water moves into a cell  Hypertonic solution: solute concentration is higher outside of cell than inside  Water moves out of a cell  62 The Principle of Osmosis Cytoplasm Solute Plasma membrane Cell wall Water Isotonic solution. Hypotonic solution. Hypertonic solution. No net movement of Water moves into the Water moves out of water occurs. cell. If the cell wall is the cell, causing its strong, it contains the cytoplasm to shrink swelling. If the cell (plasmolysis). wall is weak or damaged, the cell bursts (osmotic lysis).  63 Active Processes  Active transport: requires a transporter protein and ATP  Goes against gradient  Not altered as it crosses  Group translocation: requires a transporter protein and phosphoenolpyruvic acid (PEP) for energy  Goes against gradient  Substance is altered as it crosses the membrane  64 Animation: Active Transport  65 Animation: Types of Active Transport  66 Cytoplasm  The substance inside the plasma membrane  Eighty percent water plus proteins, carbohydrates, lipids, and ions  Houses the chromosome, plasmids, ribosomes, granules, and cytoskeleton  67 Bacterial Genetic Information  Bacterial chromosome: circular thread of DNA that contains the cell's genetic information required for survival  Most bacteria have just one chromosome  Found in the nucleoid region of the cell  Copied with the bacterial cell to the next generation  Plasmids: circular extrachromosomal genetic elements; carry non-crucial genes (e.g., antibiotic resistance, production of toxins) the cell can survive without  Can be zero to many per cell  May or may not be copied to the next generation  68 Bacterial Ribosomes  Sites of protein synthesis  Made of protein and ribosomal RNA (rRNA)  Bacteria have 70S (Svedberg Units) ribosomes  Composed of 50S (large) + 30S (small) subunits  Eukaryotes have 80S ribosomes (made of 60S and 40S subunits)  69 Inclusions (Storage Bodies)  Metachromatic granules (volutin): phosphate reserves  Polysaccharide granules: energy reserves  Lipid inclusions: energy reserves  Sulfur granules: energy reserves  Carboxysomes: RuBisCO enzyme for CO2 fixation during photosynthesis  Gas vacuoles: protein-covered cylinders that maintain buoyancy  Magnetosomes: iron oxide inclusions; destroy H2O2  70 Magnetosomes  71 Bacterial Endospores  Are resting cells produced when nutrients are depleted or conditions are stressful  Resistant to desiccation, heat, chemicals, and radiation  Produced by Bacillus and Clostridium genera  Sporulation: endospore formation by a vegetative cell  Germination: endospore returns to a vegetative state  72 Formation of Endospores by Sporulation  73 Formation of Endospores by Sporulation  74 End of Topic 1.3