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Transcript
The Shape of Things = Morphology Two main shapes of bacteria: LECTURE 3 !"#$%&'()*+ Spheres - cocci (singular = coccus) PROKARYOTIC CELL STRUCTURE Rods - bacilli (singular = bacillus) Other shapes: We’ll mostly discuss Bacteria, more about Archaea and Eukarya Later. Comma shaped - vibrio Spiral - spirilla, spirochete Varying shapes - pleomorphic Unusual cell shapes !"#$%&'()*, Cell grouping e.g. Neisseria Fig. 11.2. Methanosarcina sp. (an Archaea) note the packets of 4 or more cells…. Some Bacteria have even more elaborate morphologies….. e.g. Streptococcus e.g. Sarcina (symmetrical packet of 4 or more cells) !"#$%&'()** e.g. Staphylococcus Fig. 11.7. Complex multicellular morphology in various cyanobacteria: a. Spiral trichome of Spirulina b. Oscillatoria Fig. 11.19. Filamentous hyphae of an Actinobacterium, Streptomyces sp. Note multicellular hyphae and spherical spores (conidia). Back to a single Bacterial cell…. Fig. 11.18. Very complex multicellular, macroscopic, fruiting bodies of the Myxobacteria. Fig. 3.23 The Plasma Membrane Every cell, whether prokaryotic or eukaryotic, has a plasma membrane. Very thin -about 8 nm thick Separates the inside of the cell from the environment Current model of membrane structure is the Fluid-Mosaic model Functions of the Plasma Membrane: **It is a permeability barrier - prevents leakage of cell materials into and out of cell It is a device for energy conservation. The membrane can separate protons (H+) from hydroxyl ions (OH-) across its surface. This is called the proton motive force and is used to generate the cell’s energy currency, ATP. Fig. 3.24 Permeability of the Cytoplasmic Membrane: Osmosis Group Translocation Fig. 3.25 Generation of Energy: Proton Motive Force Fig. 3.26 Directed Movement of Molecules Fig. 3.27 ACTICE TRANSPORT Fig. Fig. 3.28 Fig. 3.30 Why do bacteria have cell walls? With all of the dissolved solutes in a cell, the turgor pressure is about 2 atmospheres - or about the same pressure as in a car tire! Cell walls help withstand these pressures and give the cells shape. The Structure of Peptidoglycan Fig. 3.32 Gram positive Cell Walls Impt. for immune recognition of bacteria Gram negative Cell Walls Lipopolysaccharide - LPS Impt. for immune recognition of bacteria Fig. 3.33 Fig. 3.35 How does the Gram stain work? The best hypothesis is: Ecological significance of Gram - and Gram + cell walls? Which would resist drying better? Thick peptidoglycan, pores close, prevent CV from escaping Components External to the Cell Wall Components External to the Cell Wall Slime layer - unorganized material that is removed easily Glycocalyx Capsule - a layer of well organized material, not easily washed off. S-layer - a regularly structured layer composed of protein or glycoprotein May help resist phagocytosis May perform many functions: • protect against ionic fluctuations • protect against predation • attach to surfaces and other cells Filamentous protein appendages • Flagella • Pili Fimbria(e) - pili used to attach to surfaces Pili (fimbriae) Pili (sing. = pilus) - larger, genetically determined by sex factors and used for mating. Figure 8.17 !"#$%&'()-* Flagella & Motility Flagella (sing. = flagellum) are used for locomotion. Flagella may be distributed in specific patterns: monotrichous lophotrichous amphitrichous peritrichous Fig. 3.18. Flagella visualized with a stain that coats them with a thick layer of stain so that they can be seen with the light microscope. Fig. 3.38 a. Peritrichous flagella visualized with a scanning electron microscope (SEM) Flagella are composed of 3 parts: • the filament • the basal body • the hook b. Polar flagellum visualized with an SEM. Fig. 3.39 The direction of the rotation determines how the cell moves. Chemotaxis In a constant environment, bacteria will move randomly. They can, however, exhibit directed movement toward an attractant (e.g. food) or away from a repellant (e.g. waste). This is chemotaxis. See Fig. 3.40 Bacteria rotate their flagella very rapidly - as much as 1000 rps! Although bacteria only move 0.00017 km/hr, this equates to 50-60 cell lengths/sec. In contrast, a cheetah can only run at a rate of 25 body lengths/sec! The Cytoplasmic Matrix Unlike eukaryotes, bacteria do not have membrane-bound organelles. The cytoplasmic matrix is the material between the plasma membrane and the nucleoid. What’s in there? • Ribosomes • Cytoskeleton-like system of proteins Ribosomes Storage granules (a type of inclusion body) RNA + proteins Some are membrane-bound, most aren’t. Site of protein synthesis Used for storage: • carbon compounds • inorganic substances • energy Reduce osmotic pressure Granules Inclusion Bodies (cont.): Photosynthetic bacteria have gas vacuoles that they can fill with air. This gives them buoyancy so they can stay near the surface of the water and close to sunlight. They can regulate their buoyancy by collapsing vacuoles and constructing new ones. !"#$%&'()-.)''/01234&563728%0924$52%65&':;65'<50%6#&= The Nucleoid How big are bacterial genomes? Bacteria usually have 1 “chromosome” in an irregularly shaped region, the nucleoid. 1 million - 10 million base pairs !"#$%&'()-('>56"?&8'@AB':?$C1&0"8= If stretched out, the E. coli genome would be about 1 mm in length, but the bacteria itself is only 2-3 !m long! !"#$%&'()-()'' D)'C01"''@AB';%0E'4$%<5'C&11 The DNA in the nucleoid is supercoiled to package it compactly. Many bacteria also contain plasmids. The Endospore Gram + - very resistant, dormant structure These are also circular. Cannot be killed by boiling - must be autoclaved. Plasmids are typically Makes them dangerous pathogens, but most endospore formers are not pathogens. passed on to all daughter cells. They are generally not essential for survival, but very often contain genes that provide a selective advantage, such as antibiotic resistance. The structure of an endospore is complex: Endospore formation CW = core wall CX = cortex SC = spore coat EX = exosporium CR = core N = nucleoid !"#$%&'()-F Fig. 26.12 Fig. 11.16 Bacillus anthracis (spores in middle of cells) Clostridium botulinum (Spores at ends of cells) Clostridium tetani (spores at ends of cells)