Lecture Power Point to accompany Microbiology Chapter 4

Lecture Power. Point to accompany Microbiology Chapter 4 An Introduction to the Prokaryotic Cell, Its Organization, and Members Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

4. 1 Characteristics of Cells and Life All living things (single and multicellular) are made of cells that share some common characteristics: – Basic shape – spherical, cubical, cylindrical – Internal content – cytoplasm, surrounded by a membrane – DNA chromosome(s), ribosomes, metabolic capabilities Two basic cell types: eukaryotic and prokaryotic 2

Characteristics of Cells Eukaryotic cells: animals, plants, fungi, and protists – Contain membrane-bound organelles that compartmentalize the cytoplasm and perform specific functions – Contain double-membrane bound nucleus with DNA chromosomes Prokaryotic cells: bacteria and archaea – No nucleus or other membrane-bound organelles 3

Characteristics of Life • Reproduction and heredity – genome composed of DNA packed in chromosomes; produce offspring sexually or asexually • Growth and development • Metabolism – chemical and physical life processes • Movement and/or irritability – respond to internal/external stimuli; self-propulsion of many organisms • Cell support, protection, and storage mechanisms – cell walls, vacuoles, granules and inclusions • Transport of nutrients and waste 4

Figure 4. 1 Structure of a bacterial cell 5

4. 3 Prokaryotic Profiles 6

Prokaryotic Profiles • Structures that are essential to the functions of all prokaryotic cells are a cell membrane, cytoplasm, ribosomes, and one (or a few) chromosomes 7

4. 3 External Structures • Appendages – Two major groups of appendages: • Motility – flagella and axial filaments (periplasmic flagella) • Attachment or channels – fimbriae and pili • Glycocalyx – surface coating 8

Figure 4. 4 The operation of flagella https: //youtu. be/QTPRXur. QUVg 9

Flagellar Arrangements 1. Monotrichous – single flagellum at one end 2. Lophotrichous – small bunches emerging from the same site 3. Amphitrichous – flagella at both ends of cell 4. Peritrichous – flagella dispersed over surface of cell; slowest 10

Flagellar Responses Guide bacteria in a direction in response to external stimulus: Chemical stimuli – chemotaxis; positive and negative Light stimuli – phototaxis Signal sets flagella into rotary motion clockwise or counterclockwise: Counterclockwise – results in smooth linear direction – run Clockwise – tumbles 11

Figure 4. 5 Chemotaxis in bacteria 12

Periplasmic Flagella • Internal flagella, enclosed in the space between the outer sheath and the cell wall peptidoglycan • Produce cellular motility by contracting and imparting twisting or flexing motion 13

Figure 4. 3 Electron micrographs of flagellar arrangements http: //glencoe. mheducation. com/olc web/cgi/pluginpop. cgi? it=swf: : 640: : 480: : /sites/dl/free/0003292010/811 339/Bacterial_Locomotion. swf: : Ba cterial%20 Locomotion 14

Which of the following best describes the action of the prokaryotic flagellum? A. IT WHIPS BACK & FORTH TO MOVE THE CELL B. IT EXTENDS AN CONTRACTS TO MOVE THE CELL C. IT ROTATES TO MOVE THE CELL D. IT ATTACHES TO THE ENVIRONMNET AND PULLS THE CELL AHEAD E. IT IS CAPABLE OF ALL OF THE ABOVE 15

Flagella • 3 parts: – Filament – long, thin, helical structure composed of protein Flagellin – Hook – curved sheath – Basal body – stack of rings firmly anchored in cell wall • Rotates 360 o • Number and arrangement of flagella varies: – Monotrichous, lophotrichous, amphitrichous, peritrichous • Functions in motility of cell through environment 16

Figure 4. 2 Flagella 17

Fimbriae • Fine, proteinaceous, hairlike bristles emerging from the cell surface • Function in adhesion to other cells and surfaces 18

Pili • Rigid tubular structure made of pilin protein • Found only in gram-negative cells • Function to join bacterial cells for partial DNA transfer called conjugation CONJUGATION = BACTERIA SEX 19

Glycocalyx • • Coating of molecules external to the cell wall, made of sugars and/or proteins Two types: 1. Slime layer - loosely organized and attached 2. Capsule - highly organized, tightly attached 20

• Functions: – – – Protect cells from dehydration and nutrient loss Inhibit killing by white blood cells by phagocytosis, contributing to pathogenicity Attachment - formation of biofilms Bio. Films Video http: //glencoe. mheducation. com/olcweb/cgi/plugin pop. cgi? it=swf: : 640: : 480: : /sites/dl/free/0003292010 /811339/Biofilm_Formation. swf: : Biofilm%20 For mation 21

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Figure 4. 11 Biofilm on a catheter 23

4. 4 The Cell Envelope • External covering outside the cytoplasm • Composed of two basic layers: – Cell wall and cell membrane • Maintains cell integrity • Two different groups of bacteria demonstrated by Gram stain: – Gram-positive bacteria: thick cell wall composed primarily of peptidoglycan and cell membrane – Gram-negative bacteria: outer cell membrane, thin peptidoglycan layer, and cell membrane 24

Structure of Cell Walls • Determines cell shape, prevents lysis (bursting) or collapsing due to changing osmotic pressures • Peptidoglycan is primary component: – Unique macromolecule composed of a repeating framework of long glycan chains cross-linked by short peptide fragments 25

• GRAM POSTIVE CELL Wall • Thick, homogeneous sheath of peptidoglycan – 20 -80 nm thick – Includes teichoic acid and lipoteichoic acid: function in cell wall maintenance and enlargement during cell division; move cations across the cell envelope; stimulate a specific immune response – Some cells have a periplasmic space, between the cell membrane and cell wall 26

Figure 4. 12 27

Gram-Negative Cell Wall • Composed of an outer membrane and a thin peptidoglycan layer • Outer membrane is similar to cell membrane bilayer structure – Outermost layer contains lipopolysaccharides and lipoproteins (LPS) • Lipid portion (endotoxin) may become toxic when released during infections • May function as receptors and blocking immune response • Contain porin proteins in upper layer – regulate molecules entering and leaving cell – Bottom layer is a thin sheet of peptidoglycan • Periplasmic space above and below peptidoglycan 28

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Table 4. 1 Comparison of Gram-Positive and Gram-Negative 30

• • • Which of the following is not found in a Gram negative structure A. Porins B. Teichoic Acids C. Periplasmic Space D. Lipopolysaccharides E. Peptidoglycan 31

The Gram Stain • Differential stain that distinguishes cells with a grampositive cell wall from those with a gram-negative cell wall – Gram-positive - retain crystal violet and stain purple – Gram-negative - lose crystal violet and stain red from safranin counterstain • Important basis of bacterial classification and identification • Practical aid in diagnosing infection and guiding drug treatment • Gram stain technique: http: //glencoe. mheducation. com/olcweb/cgi/pluginpop. 32 cgi? it=swf: : 640: : 480: : /sites/dl/free/0003292010/8113

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Nontypical Cell Walls • Some bacterial groups lack typical cell wall structure, i. e. , Mycobacterium and Nocardia – Gram-positive cell wall structure with lipid mycolic acid (cord factor) • Pathogenicity and high degree of resistance to certain chemicals and dyes • Basis for acid-fast stain used for diagnosis of infections caused by these microorganisms • Some have no cell wall, i. e. , Mycoplasma – Cell wall is stabilized by sterols – Pleomorphic ( weird infections) 34

Figure 4. 15 Extreme variation in shape of Mycoplasma pneumoniae 35

Cell Membrane Structure • Phospholipid bilayer with embedded proteins – fluid mosaic model • Functions in: – Providing site for energy reactions, nutrient processing, and synthesis – Passage of nutrients into the cell and the discharge of wastes • Cell membrane is selectively permeable 36

Figure 4. 16 Cell membrane structure 37

4. 5 Bacterial Internal Structures • Cell cytoplasm: – Dense gelatinous solution of sugars, amino acids, and salts – 70 -80% water • Serves as solvent for materials used in all cell functions 38

Nucleiod • Chromosome – Single, circular, double-stranded DNA molecule that contains all the genetic information required by a cell • Plasmids – Small circular, double-stranded DNA( 10, 000 base pairs – Free or integrated into the chromosome – Duplicated and passed on to offspring – Not essential to bacterial growth and metabolism – May encode antibiotic resistance, tolerance to toxic metals, enzymes, and toxins 39

Figure 4. 17 Chromosome structure 40

Bacterial Internal Structures • Plasmids – Small circular, double-stranded DNA – Free or integrated into the chromosome – Duplicated and passed on to offspring – Not essential to bacterial growth and metabolism – May encode antibiotic resistance, tolerance to toxic metals, enzymes, and toxins – Used in genetic engineering - readily manipulated and transferred from cell to cell 41

Bacterial Internal Structures • Ribosomes – Made of 60% ribosomal RNA and 40% protein – Consist of two subunits: large and small – Prokaryotic differ from eukaryotic ribosomes in size and number of proteins – Site of protein synthesis – Present in all cells 42

Figure 4. 18 Prokaryotic ribosome 43

Bacterial Internal Structures • Cytoskeleton – Many bacteria possess an internal network of protein polymers that is closely associated with the cell wall 44

Bacterial Internal Structures • Endospores – Inert, resting, cells produced by some G+ genera: Clostridium, Bacillus, and Sporosarcina • Have a 2 -phase life cycle: – Vegetative cell – metabolically active and growing – Endospore – when exposed to adverse environmental conditions; capable of high resistance and very long-term survival – Sporulation - formation of endospores • Hardiest of all life forms • Withstands extremes in heat, drying, freezing, radiation, and chemicals • Not a means of reproduction – Germination - return to vegetative growth 45

Figure 4. 22 Sporulation cycle http: //glencoe. mheducation. com/olcweb/cgi/pluginpop. cgi? it=swf: : 64 0: : 480: : /sites/dl/free/0003292010/811339/Bacterial_Spore_Formation. swf: : Bacterial%20 Endospore%20 Formation 46

Endospores • Resistance linked to high levels of calcium and dipicolinic acid • Dehydrated, metabolically inactive • Thick coat • Longevity verges on immortality, 250 million years • Resistant to ordinary cleaning methods and boiling • Pressurized steam at 120 o. C for 20 -30 minutes will destroy 47

4. 6 Bacterial Shapes, Arrangements, and Sizes • Vary in shape, size, and arrangement but typically described by one of three basic shapes: – Coccus – spherical – Bacillus – rod • Coccobacillus – very short and plump • Vibrio – gently curved – Spirillum – helical, comma, twisted rod, • Spirochete – spring-like 48

Figure 4. 23 Common bacterial shapes 49

Bacterial Shapes, Arrangements, and Sizes http: //glencoe. mheducation. com/olcweb/cgi/pluginpop. cgi? it=swf: : 640: : 480: : /sites/dl/free/0003292010/811339/Procaryotic. swf: : Proca ryotic%20 Cell%20 Shapes • Arrangement of cells is dependent on pattern of division and how cells remain attached after division: – Cocci: • • • Singles Diplococci – in pairs Tetrads – groups of four Irregular clusters Chains Cubical packets (sarcina) – Bacilli: • Diplobacilli • Chains • Palisades 50

Table 4. 2 Comparison of Spiral-Shaped Bacteria 51

4. 7 Classification Systems in the Prokaryotae 1. Microscopic morphology- gram stain 2. Macroscopic morphology – colony appearance 3. Bacterial physiology- how they grow what do they look like 4. Serological analysis- antibody/ antigen test 5. Genetic and molecular analysis 52

Bacterial Taxonomy Based on Bergey’s Manual • Bergey’s Manual of Determinative Bacteriology – five volume resource covering all known prokaryotes – Classification based on genetic information – phylogenetic – Two domains: Archaea and Bacteria – Five major subgroups with 25 different phyla 53

Species and Subspecies • Species – a collection of bacterial cells which share an overall similar pattern of traits in contrast to other bacteria whose pattern differs significantly • Strain or variety – a culture derived from a single parent that differs in structure or metabolism from other cultures of that species (biovars, morphovars) • Type – a subspecies that can show differences in antigenic makeup (serotype or serovar), susceptibility to bacterial viruses (phage type) and in pathogenicity (pathotype) 54

Prokaryotes with Unusual Characteristics • Free-living nonpathogenic bacteria • Photosynthetic bacteria – use photosynthesis, can synthesize required nutrients from inorganic compounds – Cyanobacteria (blue-green algae) • Gram-negative cell walls • Extensive thylakoids with photosynthetic chlorophyll pigments and gas inclusions – Green and purple sulfur bacteria • Contain photosynthetic pigment bacteriochlorophyll • Do not give off oxygen as a product of photosynthesis – Gliding, fruiting bacteria • Gram-negative • Glide over moist surfaces 55

Figure 4. 28 Structure of cyanobacteria 56

Figure 4. 29 Photosynthetic bacteria 57

Unusual Forms of Medically Significant Bacteria • Obligate intracellular parasites – Rickettsias • Very tiny, gram-negative bacteria • Most are pathogens that alternate between mammals and blood-sucking arthropods • Obligate intracellular pathogens • Cannot survive or multiply outside of a host cell • Cannot carry out metabolism on their own • Rickettsia rickettisii – Rocky Mountain spotted fever • Rickettsia typhi – endemic typhus 58

Unusual Forms of Medically Significant Bacteria – Chlamydias • • Tiny Obligate intracellular parasites Not transmitted by arthropods Chlamydia trachomatis – severe eye infection and one of the most common sexually transmitted diseases • Chlamydia pneumoniae – lung infections 59

4. 8 Archaea: The Other Prokaryotes • Constitute third Domain Archaea • Seem more closely related to Domain Eukarya than to bacteria • Contain unique genetic sequences in their r. RNA • Have unique membrane lipids and cell wall construction • Live in the most extreme habitats in nature, extremophiles • Adapted to heat, salt, acid p. H, pressure, and atmosphere • Includes: methane producers, hyperthermophiles, extreme halophiles, and sulfur reducers 60

Archaea 61

Table 4. 5 Comparison of Three Cellular Domains 62