chapt04_lecture. T7

Foundations in MicrobiologySeventh Edition : 

Foundations in MicrobiologySeventh Edition Chapter 4 An Introduction to the Prokaryotic Cell, Its Organization, and Members Lecture PowerPoint to accompany Talaro Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Chapter 4: An Introduction to the Prokaryotic Cell, Its Organization, and Members : 

Chapter 4: An Introduction to the Prokaryotic Cell, Its Organization, and Members Features of the prokaryotic cell presented include motility, cell envelope, cell wall, cell membrane, chromosomes, ribosomes, inclusion bodies, and cytoskeleton. The structural and functional differences between the gram-positive cell wall and the gram-negative cell wall are elucidated. Unique capabilities of some bacteria are discussed such as the ability to form endospores and perform photosynthesis. The bacterial shapes, arrangements, and classification systems are stressed. Methods used in prokaryote identification are examined. Archaea are presented, and their extreme adaptability and unique metabolism are discussed. 2

Learning Objectives : 

Learning Objectives Eukaryotic cells (found in animals, plants, fungi, and protests) contain organelles; prokaryotic cells (found in bacteria and archaea) do not contain organelles. Prokaryotic cells can perform nearly every activity that eukaryotic cells can, and they function in ways that eukaryotic cells cannot function. The six properties of living things include growth, reproduction, metabolism, movement, cell support, and transportation of substances. DNA is the hereditary material of an organism, located in chromosomes. In prokaryotic cell metabolism, specialized areas of the cell membrane play the same role as organelles do in eukaryotes. 3

Learning Objectives : 

Learning Objectives Prokaryotic cells have the capacity to respond to stimuli. The majority of prokaryotes have cell walls which differ in composition from eukaryotic cell walls. Prokaryotes have a cell structure that is very adaptable and versatile. Bacterial flagella provide motility, have a unique construction, and allow for chemotaxis. Bacterial fimbriae provide attachment, while sex pili provide a means of genetic exchange. 4

Learning Objectives : 

Learning Objectives For protection against severe conditions bacteria produce a glycocalyx. The bacterial cell envelope is composed of a cell wall and a cell membrane. The cell walls of most bacteria contain peptidoglycan which provides support and stability. Bacteria are often grouped according to their ability to entrap crystal violet within their peptidoglycan (gram-positive versus gram-negative). Gram-positive bacteria have a thick cell wall composed of peptidoglycan which lies in very close proximity to the cell membrane. 5

Learning Objectives : 

Learning Objectives Gram-negative bacteria have an outer membrane made of lipopolysaccharide, a thin shell of peptidoglycan, a periplasmic space, and a cell membrane. Several groups of bacteria lack the cell wall structure of gram-positive or gram-negative bacteria, and some completely lack a cell wall. In bacteria that lack a cell wall entirely, the cell membrane provides the structural support. The model of the bacterial cell membrane is called the fluid mosaic model. The bacterial cell membrane is a place for metabolism, nutrient processing, and transport. 6

Learning Objectives : 

Learning Objectives The bacterial chromosome is a single circular strand found in a central area of the cell termed the nucleoid. Bacteria contain thousands of ribosomes which play a crucial role in protein synthesis. Bacteria store nutrients in inclusion bodies, during times of nutrient abundance. Many bacteria contain an internal network of protein polymers that are associated with the cell wall. Endospores are dormant bodies, formed by some bacteria, that are extremely resistant to heat and desiccation. 7

Learning Objectives : 

Learning Objectives Most bacteria can be described by three general shapes (coccus, bacillus, and spiral). Morphology, physiology, serological analysis, and genetic techniques are all important in identifying bacteria. Most bacteria obtain their nutrients from other organisms but photosynthetic bacteria can use the energy from sunlight to synthesize nutrients. Bacteria that are considered obligate intracellular parasites cannot survive outside a host cell. Archaea have unique metabolism, genetics, and numerous adaptations that differ from bacteria. 8

Key Terms : 

Key Terms cells cytoplasm organelles reproduction metabolism genome chromosomes sexual reproduction asexual reproduction mitosis ribosomes endoplasmic reticulum mitochondria chloroplasts irritability motility Golgi apparatus bacteria appendages flagellum filament basal body hook polar 9

Key Terms : 

Key Terms monotrichous lophotrichous amphitrichous peritrichous chemotaxis spirochetes fimbria pilus conjugation glycocalyx slime layer capsule gram stain peptidoglycan lysis periplasmic space outer membrane lipopolysaccharide lipoproteins porins acid-fast stain mycoplasmas pleomorphism 10

Key Terms : 

Key Terms L-forms protoplast spheroplast cytoplasmic membrane fluid mosaic model mesosomes bacterial chromosome nucleoid plasmids ribosomes inclusion bodies metachromatic granules bacterial actin endospore sporulation sporangium coccus bacillus coccobacillus vibrio spirillum 11

Key Terms : 

Key Terms diplococci tetrads staphylococci micrococci sarcina palisades phenetic phylogenetic domain archaea domain bacteria phylum proteobacteria rickettsias phylum firmicutes phylum actinobacteria strains types thylakoids obligate intracellular parasites 12

4.1 Characteristics of Cells and Life : 

13 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

Characteristics of Cells : 

14 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

Characteristics of Life : 

15 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

4.3 Prokaryotic Profiles : 

4.3 Prokaryotic Profiles 16

Prokaryotic Profiles : 

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 17

Figure 4.1 Structure of a bacterial cell : 

Figure 4.1 Structure of a bacterial cell 18

4.3 External Structures : 

19 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

Flagella : 

20 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 360o Number and arrangement of flagella varies: Monotrichous, lophotrichous, amphitrichous, peritrichous Functions in motility of cell through environment

Figure 4.2 Flagella : 

Figure 4.2 Flagella 21

Flagellar Arrangements : 

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

Figure 4.3 Electron micrographs of flagellar arrangements : 

Figure 4.3 Electron micrographs of flagellar arrangements 23

Flagellar Responses : 

24 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

Periplasmic Flagella : 

25 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

Figure 4.6 Periplasmic flagella : 

Figure 4.6 Periplasmic flagella 26

Fimbriae : 

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

Pili : 

28 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

Glycocalyx : 

29 Glycocalyx Coating of molecules external to the cell wall, made of sugars and/or proteins Two types: Slime layer - loosely organized and attached Capsule - highly organized, tightly attached Functions: Protect cells from dehydration and nutrient loss Inhibit killing by white blood cells by phagocytosis, contributing to pathogenicity Attachment - formation of biofilms

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Figure 4.11 Biofilm on a catheter : 

Figure 4.11 Biofilm on a catheter 31

4.4 The Cell Envelope : 

32 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

Figure 4.12 : 

Figure 4.12 33 Insert figure 4.12 Comparative cell envelopes

Structure of Cell Walls : 

34 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

Figure 4.13 Peptidoglycan : 

Figure 4.13 Peptidoglycan 35

Gram-Positive Cell Wall : 

36 Gram-Positive 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

Figure 4.12 : 

Figure 4.12 37

Gram-Negative Cell Wall : 

38 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 (as opposed to an exotoxin) 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

Endotoxins : 

Endotoxins A bacterial toxin not freely liberated into the surrounding medium, in contrast to exotoxin. The complex phospholipid-polysaccharide macromolecules that form an integral part of the outer membrane of a variety avirulent and virulent strains of gram-negative bacteria. The toxins are relatively heat stable, less potent and less specific than most exotoxins. On injection, they may cause a state of shock and, in smaller doses, fever and leukopenia followed by leukocytosis. 39

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Table 4.1 Comparison of Gram-Positive and Gram-Negative : 

Table 4.1 Comparison of Gram-Positive and Gram-Negative 41

The Gram Stain : 

42 The Gram Stain Differential stain that distinguishes cells with a gram-positive 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

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Nontypical Cell Walls : 

44 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

Figure 4.15 Extreme variation in shape of Mycoplasma pneumoniae : 

Figure 4.15 Extreme variation in shape of Mycoplasma pneumoniae 45

Cell Membrane Structure : 

46 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

Figure 4.16 Cell membrane structure : 

Figure 4.16 Cell membrane structure 47

4.5 Bacterial Internal Structures : 

48 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

Bacterial Internal Structures : 

49 Chromosome Single, circular, double-stranded DNA molecule that contains all the genetic information required by a cell Aggregated in a dense area called the nucleoid DNA is tightly coiled Bacterial Internal Structures

Bacterial Internal Structures : 

50 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

Bacterial Internal Structures : 

51 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

Figure 4.18 Prokaryotic ribosome : 

Figure 4.18 Prokaryotic ribosome 52

Bacterial Internal Structures : 

53 Bacterial Internal Structures Inclusions and granules Intracellular storage bodies Vary in size, number, and content Bacterial cell can use them when environmental sources are depleted Examples: glycogen, poly b-hydroxybutyrate, gas vesicles for floating, sulfur and phosphate granules (metachromatic granules), particles of iron oxide

Bacterial Internal Structures : 

Bacterial Internal Structures Cytoskeleton Many bacteria possess an internal network of protein polymers that is closely associated with the cell wall 54

Bacterial Endospores: An Extremely Resistant Life Form : 

55 Bacterial Endospores: An Extremely Resistant Life Form 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

Endospores : 

56 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 121oC, 15 psi, 20 minutes average

4.6 Bacterial Shapes, Arrangements, and Sizes : 

57 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

Figure 4.23 Common bacterial shapes : 

Figure 4.23 Common bacterial shapes 58

Table 4.2 Comparison of Spiral-Shaped Bacteria : 

Table 4.2 Comparison of Spiral-Shaped Bacteria 59

Bacterial Shapes, Arrangements, and Sizes : 

60 Bacterial Shapes, Arrangements, and Sizes 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

Figure 4.25 Arrangement of cocci : 

Figure 4.25 Arrangement of cocci 61

Figure 4.26 The dimensions of bacteria : 

Figure 4.26 The dimensions of bacteria 62

4.7 Classification Systems in the Prokaryotae : 

63 4.7 Classification Systems in the Prokaryotae Microscopic morphology Macroscopic morphology – colony appearance Bacterial physiology Serological analysis Genetic and molecular analysis

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Major Taxonomic Groups of Bacteria : 

65 Major Taxonomic Groups of Bacteria Domain Archaea – primitive, adapted to extreme habitats and modes of nutrition Domain Bacteria: Phylum Proteobacteria – Gram-negative cell walls Phylum Firmicutes – mainly gram-positive with low G + C content Phylum Actinobacteria – Gram-positive with high G + C content

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Species and Subspecies : 

67 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)

Prokaryotes with Unusual Characteristics : 

68 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

Unusual Forms of Medically Significant Bacteria : 

69 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

Unusual Forms of Medically Significant Bacteria : 

70 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

4.8 Archaea: The Other Prokaryotes : 

71 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 rRNA Have unique membrane lipids and cell wall construction Live in the most extreme habitats in nature, extremophiles Adapted to heat, salt, acid pH, pressure, and atmosphere Includes: methane producers, hyperthermophiles, extreme halophiles, and sulfur reducers

Archaea : 

Archaea 72

Table 4.5 Comparison of Three Cellular Domains : 

Table 4.5 Comparison of Three Cellular Domains 73