Topic 03 Prokaryotes (3.3)

Transcription

1 Topic 03 Prokaryotes (3.3) Topics Characteristics (comparison) External Structures Cell Envelope Internal Structures Cell Shapes, Arrangement, and Sizes Classification 1 Relative size of bacterial cell compared to other cells, including viruses. 2 Comparison (Pro vs. Eu) No nuclear membrane um No membrane bound organelles Simple flagella, 2 proteins Glycocalyx: capsule or slime layers True nucleus um Organelles (lysosomes, Golgi, ER, etc.) Complex flagella, microtubules Possibly in those w/o cell wall 3 1

2 Comparison (cont.) Complex cell wall (incl. peptidoglycan) Plasma membrane: few if any sterols, no carbos No cytoskeleton or cyto streaming Simple cell wall, if present Plasma membrane: sterols and carbos Cytoskeleton, cyto streaming 4 Comparison (cont...) Small Ribosomes- 70S DNA: Single, circular, no histones Binary fission Recombination: no meiosis, fragment transfer only Large ribosomes - 80S + 70S in organelles DNA: Multiple, linear, w/ histones Mitosis Recombination: meiosis 5 Bacteria No membrane bounded organelles Peptidoglycans Antibiotic sensitivity Binary fission No Histones 70S ribosome 6 2

3 Typical prokaryotic cell 7 Figure 3.2 Internal Structures Cytoplasm Genetic structures Ribosomes (50S) Storage bodies (inclusion bodies) Nucleoid Endospore (survival, triple-walled) 8 Cytoplasm Gelatinous solution containing water, nutrients, proteins, and genetic material. Site for cell metabolism 9 3

4 Genetic structures Deoxyribonucleic acid (DNA) - circular Ribonucleic acid (RNA) Ribosomes (70S = 50S+30S) Images from: (dna) (ribosome): 10 Ribosomes Ribosome: a combination of RNA and protein involved in protein synthesis. 2 subunits Model of a prokaryotic ribosome. 11 Example Inclusions (A) TEM - Polyhydroxybutryrate Lipid Droplets (B) LM - Volutin Granules (C) Phase-Contrast - Sulfur Granules (D) TEM - Magnetosomes (E) TEM - Gas Vacuoles 12 4

5 Nucleoid Example 13 Endospores (some, not all) a Carboxydothermus hydrogenoformans endospore* *Thermophile, G+, H 2 waste 14 Common Prokaryotic Cell Shapes Coccus Bacillus Vibrio Coccobacillus Spirillum Spirochete 15 5

6 Common Prokaryotic Cell Arrangements 16 Cytoplasmic membrane Site of : Embedded proteins Energy generation Transport L-forms lose the ability to synthesize cell walls (see next slide ) 17 Plasma Membrane 18 6

7 Simple Diffusion 19 Facilitated Diffusion 20 Active Transport (Across Membrane) 21 7

8 Cell envelope Cell wall Gram-positive Gram-negative Cytoplasmic membrane Non cell wall 22 Cell wall Gram positive cell wall (+ Purple) Thick peptidoglycan (PG) layer Acidic polysaccharides Teichoic acid and lipoteichoic acid Gram-negative cell wall (- Pink) Thin PG layer Outer membrane Lipid polysaccharide Porins 23 Structures associated with gram + and gram - cell walls. Structure comparison gram-positive and gram-negative cell walls. 24 8

9 G+ vs G- Peptidoglycan 25 G+ vs G- 26 Mycolic Acid Mycobacteria! 27 9

10 LPS a source of trouble! Gram-negative bacteria Lipopolysaccharide (LPS), a toxin composed of : 1. Lipid A embedded in the outer membrane, 2. a core polysaccharide, 3. and the O side chain. Promotes secretion of pro-inflammatory cytokines, nitric oxide, and eicosanoids Causes cellular stress response LPS is also an exogenous pyrogen (fever-inducing substance) 28 Glycocalyx Capsule Protects bacteria from immune cells (sticky) Slime layer Enable attachment and aggregation of bacterial cells loosely bound to the cell, H 2 O soluble associated with the formation of biofilms (e.g.. on teeth) 29 Glycocalyces 30 Figure

11 The capsule is tightly bound to the cell, and is associated with pathogenic bacteria. Capsule = halo Center = bacterial cell Encapsulated bacteria 31 External Structures Flagella Pili and fimbriae Glycocalyx 32 Flagella Composed of protein subunits Motility (chemotaxis) Varied arrangement (ex. Monotrichous, lophotrichous, amphitrichous) 33 11

12 Flagella Arrangements 34 Three main parts of the flagella include the basal body, hook, and filament. 35 Different arrangements of flagella exist for different species. Some flagella arrangements

13 Pili and fimbriae Attachment Mating (Conjugation) Fimbriae: Fimbriae are smaller than flagella, and are important for attachment. Pili: Pili enable conjugation 37 The Pilus (pili) Tubules composed of pilin Longer than fimbriae but shorter than flagella Typically one or two per cell (conjugation) Three bacteria in the process of conjugating 38 Fimbriae - so what are they? Sticky, bristle like projections Used by bacteria to adhere to one another, to hosts, and to substances in environment Shorter than flagella Serve an important function in biofilms 39 13

14 L-form = No cell wall No PG layer Cell membrane contains sterols for stability Example: Mycoplasma sp. Image from: 40 Classification Phenotypic methods (biochemical + staining) Molecular methods (sequencing) Taxonomic scheme Unique groups 41 Methods of classification enable bacteria to be grouped into different divisions and classes. Bergey s Manual 42 14

15 Unique groups of bacteria Intracellular parasites (ex. Rickettsia sp.) Photosynthetic (oxygenic) bacteria (Cyanobacteria) Photosynthetic (non-oxygenic) bacteria (green and purple sulfur bacteria) Gliding and fruiting bacteria Archaea bacteria 43 Archaea bacteria Associated with extreme environments Contain unique cell walls Contain unique internal structures 44 Archae Lack peptidoglycans Have glycocalyx, flagella, fibriae, hami Inhabit extreme environments CH4 Halophiles Thermophiles No Antibiotic sensitivity (!) 70S ribosomes 45 15