Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
4-b The Bacteria pps. 77 – 106 • Bacterial cell wall • Plasma membrane • Structures internal to plasma membrane 1 http://www.microbelibrary.org/ Search: Keen The Gram Stain: An Animated Approach MicrobeLibrary Visual: Animation 12/16/2005 by Daniel Cavanaugh, Mark Keen This animation demonstrates at a molecular level the interaction of the Gram's stain reagents in a step-by-step process with both the gram-negative and gram-positive cell envelope. http://www.microbelibrary.org/Gram%20Stain/details.asp?id=2020&Lang= 2 Pili Fimbriae Flagellum Glycocalyx DNA Ribosomes Granules (inclusions) Cell membrane Plasmid Cell wall Cytoplasm 3 The Cell Wall • Semi-rigid structure made of peptidoglycan • Internal to the capsule • External to the plasma membrane Capsule Cell wall Plasma membrane 4 Functions • Maintain cell shape • Protect bacteria against osmotic lysis – Rupture of the cell resulting from movement of water into the cell • In some species, contributes to virulence • Chemical composition differentiates bacteria • Site of antibiotic damage 5 Animal cells lack cell walls Makes cell walls a good target for antibiotics – By attacking the integrity of the cell wall – Preventing peptidoglycan formation, cross-linking – Example: penicillins, cephalosporins 6 Peptidoglycan ‘network’ Repeated units of sugars and short chains of amino acids Sugars are: – N-acetylglucosamine (NAG) – N-acetylmuramic acid (NAM) – Run in ‘parallel’ throughout the cell wall – NAM links to peptide chains – Holds the whole porous ‘mesh’ together 7 Sugars Peptides Fig 4.13a Small black arrows: penicillin action on peptides 8 Gram Positive Cell Walls • Thick (~ 90%) layer of peptidoglycan (20-80 nm) • Many ‘rows’ of cross-linked peptidoglycan stacked in ‘sheets’ • Teichoic acids, lipoteichoic acid, proteins • The cell (plasma) membrane underneath the cell wall 9 Teichoic Acid Functions • May regulate movement in/out of cell • Role in growth, prevent breakdown, cell lysis • Provide antigenic specificity – Making it possible to identify bacteria 10 Gram Negative Cell Walls • Thin layer of peptidoglycan (~ 2 nm) – Only one to a few ‘rows’ / ‘sheets’ • Contains more protein than Gram + • No teichoic acids • Contains an outer membrane – A lipid bilayer membrane ‘outside’ the cell wall but connected to it 11 Outer Membrane Functions • • • • Contains channels called porins = transport Contains lipopolysaccharide (LPS) LPS consists of polysaccharide and Lipid A Lipid A known as endotoxin, cause fever, shock • O-polysaccharides – Function as antigens, cause various diseases – Useful to distinguish Gram negative bacteria – Example: E. coli O157:H7 (serovar) 12 13 Gram Stain: Differential stain… used as an initial step to identify bacteria Step Gram Positive Gram Negative Crystal violet Dye enters cytoplasm Dye enters cytoplasm Iodine Forms crystal with CV, too large to escape cell wall Forms crystal with CV, too large to escape cell wall Alcohol Dehydrates peptidoglycan, impermeable to CV-I Dissolves outer membrane, makes holes in thin peptidoglycan, CV-I can diffuse out of cell Color after alcohol Purple Colorless Safranin Purple (pink is masked by the purple dye) Pink 14 15 16 Cell Membrane The plasma membrane is inside the cell wall and encloses the cytoplasm • Phospholipid bilayer, Fluid Mosaic Model – Similar to eukaryotes 50:50 protein to lipid • Proteins include – Peripheral, integral proteins – Transmembrane proteins (active & passive transport) 17 Review Membrane Proteins Fig 4.14a 18 Cell Membrane Functions – Production of cell wall components – DNA replication – Cell respiration (ATP generation via ETS) – Act as selective or semi-permeable barrier • Control movement of substances into & out of cells 19 Cell Membrane Destruction Antimicrobial agents damage the cell membrane Alcohols Quaternary ammonium compounds Used as disinfectants Antibiotics disrupt the membrane integrity Example: polymyxins Causes leakage of cell contents Use for Gram negative bacteria, e.g., Pseudomonas 20 Cytoplasm Refers to all the contents w/in cell membrane – Water (~80%) – Proteins, enzymes – Inorganic and organic molecules – Nuclear area (nucleoid) containing DNA – Ribosomes – Inclusions (granules) – Plasmids 21 Nuclear area (nucleoid) nucleus-like • Nuclear area is where the DNA is located – Single circular molecule of double stranded DNA • The nucleoid is NOT a membrane-enclosed region Fig 4.6a 22 23 Ribosomes • Found in the cytoplasm not the nucleoid area • Organelles responsible for synthesizing proteins • Consist of protein and rRNA – Smaller than ribosomes in eukaryotic cells • 70S (50S & 30S subunits) 24 Antibiotic Inhibition • Bind to either the 30S or 50S subunits • Cause faulty protein synthesis > 30S: – Streptomycin – Gentamicin – Tetracyclines Fig 4.19 > 50S: – Erythromycin – Chloramphenicol 25 Plasmids • • • • • Circular extrachromosomal DNA Double-stranded DNA Replicates autonomously Easily passed from bacterium to bacterium Plasmid genes are not necessary for the survival of the bacterium • Carry genes coding for AB resistance 26 Antibiotic Resistance • Carry genes coding for AB resistance – Called resistance factors (R factor, p 246) – Readily shared with other bacterial cells – Spread AB resistance • Have significant medical importance • Examples: Streptomycin, Chloramphenicol, Tetracycline 27 Inclusions Reserve deposits in the cells Fig 4.20 28 Inclusions Purpose/Function Polysaccharide granules Energy reserves Lipid inclusions Energy reserves Sulfur granules Metachromatic granules (volutin) Energy reserves Phosphate reserves Carboxysomes Ribulose 1,5-diphosphate carboxylase, CO2 fixation Gas vacuoles Regulate buoyancy Magnetosomes Iron oxide (destroys H2O2) 29 Endospores Dormant ‘alternate’ life forms Bacillus Clostridium Obligate aerobes Obligate anaerobes Live in soil Normal flora: animal GI tract • Under conditions of starvation (carbon, nitrogen) – A spore forms w/in some of the bacteria • Process called:Sporulation 30 2. 1. 3. 4. Sporulation 10. 5. 9. 6. 8. See Fig. 4.21 7. 31 Structure The completed endospore consists of – Multiple layers of resistant coats • Cortex, spore coat, sometimes an exosporium – Nucleoid – Some ribosomes – RNA molecules – Enzymes 32 Functions Not a reproductive structure It is a resistant, dormant survival form – Resistant to high temperatures – Most AB’s, disinfectants – Low energy radiation – Drying, etc. • Can survive > thousands of years • Until environmental stimuli trigger – Germination 33 Diseases Harmless until they germinate But, are involved in transmission of some diseases to humans Anthrax: Bacillus anthracis Tetanus: Clostridium tetani Botulism: Clostridium botulinum Gas gangrene: Clostridium perfringens 34 Bacillus anthracis Clostridium tetani Clostridium botulinum 35 Endospore Case Study • Botulism caused by C. botulinum = normal flora of GI grazing animals • Home-canned beans – Boiled, placed in jar, lids screwed on – The lids ‘popped’ indicating a vacuum formed – Upon eating beans, person contracted botulism – Explain? 36 • Endospores of C. botulinum survive in soil – C. botulinum is an obligate anaerobe • Endospores contaminating beans are – Resistant to boiling and survive – Once vacuum is formed, environment is anaerobic – Spores are able to germinate – Vegetative cells replicate, secrete exotoxin • Cause botulism 37 Q’s 1. Which is NOT found in the cell walls of gramnegative bacteria? A. Techoic acids B. Peptidoglycan C. Porins D. Lipopolysaccharides E. Outer membrane 2. Which is an incorrect pairing? A. B. C. D. E. Metachromatic granules : polyphosphate Carboxysomes : carbon dioxide fixation Lipid inclusions : b-hydroxybutyrate Plasmids : nucleotide reserves Magnetosomes : iron oxide 38 Q’s 1. 2. 3. 4. 39 Q’s 1. __________ are the primary determinants of membrane structure, while ____________ carry out membrane function. 2. Name three infections transmitted to humans by bacterial endospores. a. __________ b. __________ c. __________ 3. The following bacterial structures increase the likelihood that bacteria will be associated with disease: capsules, fimbriae, flagella, LPS. True False 40 Appendix 41 Name the cell type:_________ 1. 6. 2. 3. 7. 4. 5. 42 Name the cell type:_________ 1. 2. 3. 4. 6. 5. 43 Q’s Match Structures to their Functions ‗ ‗ ‗ ‗ ‗ ‗ ‗ ‗ Structures 1. Cell wall 2. Endospore 3. Fimbriae 4. Flagella 5. Glycocalyx 6. Pili 7. Plasma membrane 8. Ribosomes Functions a. Attachment to surfaces b. Contains transmembrane proteins c. Motility d. Protection from changes in water pressure e. Protection from phagocytes f. Resting g. Protein synthesis h. Susceptible to leakage of cell contents by polymyxin i. Transfer of genetic material 44 Q’s Functions Match Structures to their Functions ‗ ‗ ‗ ‗ ‗ ‗ ‗ ‗ Structures 1. Inclusion 2. Volutin 3. Endospore 4. Plasmid 5. Ribosome 6. Forespore 7. Nucleoid 8. Sporulation a. A structure consisting of chromosome, cytoplasm and endospore membrane inside a bacterial cell b. The process of spore and endospore formation; also called sporogenesis c. Endoflagellum d. Stored inorganic phosphate in a prokaryotic cell e. Material held inside a cell, often consisting of reserve deposits f. A resting structure formed inside some bacteria g. The region in a bacterial cell containing the chromosome h. A small circular DNA molecule that replicates independently of the chromosome i. The site of protein synthesis in a cell, composed of RNA and protein 45 Sporulation Steps 1. 2. A vegetative cell about to enter endospore cycle A spore septum forms as the cytoplasmic membrane invaginates 3. Nucleoid becomes surrounded by membrane 4. Cytoplasmic membrane surrounds isolated nucleoid, cytoplasm & membrane from step 3 5. The forespore is completed & other DNA molecule is degraded 6. Thick protective layer, peptidoglycan, called the cortex, is synthesized between inner & outer forespore membranes 7. A second impermeable proteinaceous protective layer called the spore coat is synthesized 8. Sometimes a final layer, exosporium may be added 9. Vegetative portion of cell degrades, completed endospore released 10. Bacterial endospore is completed 46