Prokaryotic Cell Structure & Function Lecture Notes PDF

LECTURE 2: Prokaryotic Cell Structure & Function, (Chapter 3, 4). WEEK 1 CLO’S CLO 1: Compare and contrast the cellular characteristics of the various prokaryotic and eukaryotic microorganisms (including helminths) CLO 4: Distinguish infectious diseases of microbial origin, including information a...

LECTURE 2: Prokaryotic Cell Structure & Function, (Chapter 3, 4). WEEK 1 CLO’S CLO 1: Compare and contrast the cellular characteristics of the various prokaryotic and eukaryotic microorganisms (including helminths) CLO 4: Distinguish infectious diseases of microbial origin, including information about their causative agent(s), signs and symptoms, diagnostic markers, treatment, and prevention  How do prokaryotes reproduce? What are endospores? How do they help bacteria survive? What are virulence factors? What are the different categories of virulence factors and their functions? What is the difference between virulence and Guiding pathogenicity? questions for What is pathogenesis? this week: What is the difference between an endotoxin and exotoxin? Do all bacteria cause disease? What is a biofilm? What are the causative agent(s), signs and symptoms, diagnostic markers, treatment, and prevention associated with syphilis and gonorrhea? How do prokaryotes reproduce? Reproduction of Prokaryotic Cells All reproduce asexually via three main methods: ◦ Binary fission (most common form of asexual reproduction) ◦ Snapping division (variation of binary fission) ◦ Budding (bud formation)  Snapping Division Occurs in some Gram-positive species Only the inner portion of the cell wall is deposited across the dividing cell Causes tension to put on the outer layer of the old cell wall and eventually the outer wall “snaps” at its weakest point Daughter cells remain hanging together, held at an angle by a small remnant of the outer wall that acts as a hinge Figure 11.4 Snapping division, a variation of binary fission. Figure 11.6 Budding. Prokaryotic Cell Shape (Morphology) and Arrangements  Bacteria Cellular Shapes and Arrangements Cell walls help give bacterial cells their characteristic shapes. Arrangements result from two aspects of division during binary fission 1. The planes in which cells divide during binary fission 2. Whether or not the daughter cells separate completely or remain attached to each other Figure 11.1 Typical prokaryotic morphologies.  Coccus Arrangements Special nomenclature is assigned to denote these arrangements ◦ Diplococci – cocci cells that remain attached in pairs ◦ Streptococci – cocci that form long chains ◦ Tetrads – cocci that divide in two planes and remain attached ◦ Sarcinae – cocci that divide in 3 planes to form cuboidal packets ◦ Staphylococci – cocci that look like bunches of grapes and form when the planes of cell division are random Bacillus Arrangement Bacilli are less varied in their arrangements than cocci because they divide transversely (perpendicular to the long axis)  Want to Know More? Dr. Bauman’s Microbiology Video Tutor ◦ For more information, listen to Dr. Bauman describe the basic shapes of prokaryotic cells and how cell division determines cellular arrangements. Lecture 2 Video 1 Completed Lecture 2 Video 2 Content Eubacteria Cell Wall and its Clinical Significance  Prokaryotic Cell Wall Most eubacteria have cell walls composed of peptidoglycan ◦ Archaea also possess cell walls made of other types of sugars ◦ Cell walls provide structure and shape and protect cell from osmotic forces Give bacterial cells characteristic shapes Scientists describe two basic types of bacterial cell walls, Gram-positive and Gram- negative  Bacterial Cell Walls: Peptidoglycan Covers the entire surface of the bacterial cell, which must insert millions of new subunits if it is to grow and divide. ◦ A complex polysaccharide composed of two types of alternating sugar molecules, called N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) A small subset of bacteria, the mycoplasmas (i.e. Mycoplasma pneumoniae), lack cell walls entirely Two basic types of bacterial cell walls on the basis of their staining characteristics: Gram-positive and Gram-negative  Gram Positive Cell Walls ◦ Have a relatively thick layer of peptidoglycan ◦ Contain unique polyalcohols called teichoic acids ◦ Some are covalently linked to lipids, forming lipoteichoic acids that anchor peptidoglycan to cell membrane ◦ Some Gram-positive bacteria also contain a waxy lipid mycolic acid (Mycobacterium genus – i.e. Mycobacterium tuberculosis and leprae –causative agents of tuberculosis and leprosy, respectively) ◦ The thickness of the cell wall retains the crystal violet dye used in the Gram staining procedure ◦ Cells appear purple ◦ Up to 60% mycolic acid in acid-fast bacteria helps cells survive desiccation Figure 3.15a Comparison of cell walls of Gram-positive and Gram-negative bacteria Peptidoglycan layer (cell wall) Cytoplasmic membrane Gram-positive cell wall Lipoteichoic acid Teichoic acid Integral protein Gram Negative Cell Wall  Have only a thin layer of peptidoglycan  Appear pink following the Gram staining procedure  Bilayer membrane outside the peptidoglycan contains phospholipids, proteins, and lipopolysaccharide (LPS)  Have a periplasmic space which exists between the cell membrane and the outer membrane  Porin Outer membrane of cell wall Porin (sectioned) Peptidoglycan Periplasmic space layer of cell wall Cytoplasmic membrane Gram-negative cell wall Phospholipid layers n Lipopolysaccharide O side chain (LPS) (varies In Integral length and composition) proteins Core polysaccharide Figure 3.15b Comparison of cell Lipid A walls of Gram-positive and Gram- (embedded in outer Fatty acid negative bacteria membrane)  A dead Gram negative bacterial cell releases lipid A when its outer cellular membrane disintegrates  Lipid A (the lipid portion of LPS) is considered an endotoxin and may trigger fever, vasodilation, inflammation, shock, and blood clotting in humans.  Since killing large numbers of Gram-negative cells with antimicrobial drugs releases large amounts of lipid A, which might threaten the patient more than the live bacteria, any internal infection by Gram-negative bacteria is cause for concern.  Clinical Significance of Gram Staining Uses Provides preliminary information concerning the type of organisms present directly from clinical specimens or from growth on culture plates. Used in screening of sputum specimens to reveal the causative organism in bacterial pneumonia. Identifies the presence of microorganisms in normally sterile body fluids (i.e. cerebrospinal fluid, synovial fluid, etc). Hospitalization may be required when the Gram stain results indicate bacteria are present in a normally sterile body fluid. The initial choice of antibiotic therapy is guided by the Gram stain results.   Because the cell walls of Gram-positive and Gram-negative organisms differ, the Gram stain is an important diagnostic tool.  After the Gram staining procedure, Gram- negative cells appear pink, and Gram-positive cells appear purple. https://upload.wikimedia.org/wikipedia/commons/3/36/Gram_Stain_Procedure.png  The Gram-negative outer membrane can also be an impediment to the treatment of disease due to the fact that it may prevent the movement of penicillin to the underlying peptidoglycan, thus rendering the drug ineffective  Acid-fast bacteria (those containing mycolic acid within their cell walls – i.e Mycobacterium tuberculosis and Mycobacterium leprae, - do NOT stain with the Gram staining technique and thus require the Acid Fast technique for staining Dichotomous (Taxonomic) Key Used in taxonomy for identification purposes Series of paired statements worded so that only one of two “either/or” choices applies to any particular organism Useful for identification of an organism by directing user to another pair of statements, or provides name of organism Dr. Bauman’s Microbiology Video Tutor ◦For more information, listen to Dr. Bauman describe the components of the bacterial cell wall and compare and contrast Gram- positive and Gram-negative cell walls. What are virulence factors? How they cause disease (virulence)? Virulence Factors Properties of a microbe that enables it to establish itself on or within a host (via attachment and colonization) and determines the extent and severity by which it causes disease (virulence). Virulence factors help bacteria to (1) invade the host, (2) cause disease, and (3) evade host defenses. Virulence – degree of pathogenicity Pathogenicity : ability of a microorganism to cause disease Pathogenesis : Beginning of the disease process Virulence factors Virulence How are each of these components Pathogenicity related? Pathogenesis Types of Virulence Factors Virulence factors contributing to an organism’s virulence include: Adhesion factors – factors that allow for attachment to surfaces (internally and externally) Extracellular enzymes: enzymes produced and excreted by microbes that allow for invasion of host tissues Toxins: proteins and enzymes produced from pathogenic bacteria. Antiphagocytic factors: factors that allow for microbe to escape immune system surveillance Toxins Endotoxins: The lipopolysaccharide endotoxin (Lipid A) on Gram-negative bacteria cause fever, changes in blood pressure, inflammation, lethal shock, and many other toxic events. Exotoxins: Exotoxins include several types of protein toxins and enzymes produced and/or secreted from pathogenic bacteria. ◦ Major categories include: ◦ Cytotoxins ◦ Neurotoxins ◦ Enterotoxins Bacterial Cardiovascular and Systemic Diseases Septicemia, Bacteremia, and Toxemia ◦ Septicemia ◦ Any microbial infection of the blood that produces illness ◦ Bacteremia ◦ Bacterial septicemia ◦ Toxemia ◦ Release of bacterial toxins into the blood ◦ Lymphangitis ◦ Infection and inflammation of the lymphatic vessels Septicemia, Bacteremia, and Toxemia ◦ Septicemia and toxemia are caused by various bacteria ◦ Often result from opportunistic or healthcare- associated infections ◦ Septicemia is caused more often by Gram-negative bacteria ◦ Bacteria that produce capsule may resist phagocytosis ◦ Some endotoxins trigger serious signs and symptoms Septicemia ◦ Signs and symptoms are usually diagnostic ◦ Treated with prompt diagnosis and administration of antimicrobial drugs ◦ Prevention includes immediate treatment of infections ◦ Important in individuals with compromised immune systems  ◦ Septicemia is due to direct inoculation of bacteria into the blood ◦ Immunocompetent individuals rarely have septicemia ◦ Bacterial infections self-limited in these people Septicemia ◦ Gram-negative bacteria more often produce severe septicemia ◦ Due to release of endotoxin as the bacteria die ◦ Activates various defensive reactions by the body Figure 21.3 Petechiae, a sign of bacteremia. Septicemia ◦ Signs and symptoms ◦ Fever, chills, nausea, vomiting, diarrhea, and malaise ◦ Septic shock can develop rapidly ◦ Small hemorrhagic lesions called petechiae can develop ◦ Osteomyelitis occurs if bacteria invade the bones ◦ Toxemia symptoms vary depending on the toxin ◦ Exotoxins: released from living microorganisms ◦ Endotoxin: released from Gram-negative bacteria Figure 21.3 Petechiae a sign of septicemia. Figure 21.2 Lymphangitis, a sign of septicemia. Figure 21.4 Potential effects of endotoxin. Table 14.8 A Comparison of Bacterial Exotoxins and Endotoxins Not all Prokaryotes cause disease ◦ Archaea do not ◦ Normal flora lack virulence factors and as such do not cause disease under normal circumstances Of the microbes that do cause disease, they vary in their virulence. Virulence factors are encoded by genes. In Summary…. Adhesins and Biofilms  Bacterial Glycocalyces  Gelatinous, sticky substance surrounding the outside of the cell  Composed of polysaccharides, polypeptides, or both  Found in prokaryotes & eukaryotes  In prokaryotes: Provides a protective coat from host factors (i.e. immune cells)  Associated with the ability of the bacteria to establish an infection  1. Capsules ◦ Composed of organized repeating units of organic chemicals Two Types of ◦ Firmly attached to cell surface Glycocalyces ◦ Protects cells from drying out ◦ May prevent bacteria from being recognized and destroyed by host ◦ Due to chemicals in capsules being similar to those natively found in the body  ◦ Capsules of Streptococcus pneumoniae and Klebsiella pneumoniae avoid destruction by WBCs in the respiratory tract to cause pneumonia 1. Capsules ◦ Unencapsulated strains of these bacteria do not cause disease due to destruction by WBCs  Are often viscous/sticky and loosely attached to cell surface Water soluble Protects cells from drying out 2. Slime layer Sticky layer that allows prokaryotes to attach to surfaces i.e. Oral bacteria colonize teeth via slime layers, where they produce acids and cause tooth decay http://www.drueckert.com/dental-tips/permalinks/2009/09/ http://www.medicdirect.co.uk/dentalhealth/default.ihtml?step=4&pid=1049 Figure 3.5 Glycocalyces. Glycocalyces and Biofilms: Clinical Significance Infectious strains of bacteria such as Staphylococcus, Streptococcus, and Pseudomonas tend to synthesize a more elaborate glycocalyx than their corresponding non-infectious counterparts. Bacterial glycocalyces also promote the adhesion of the bacteria to living and inert surfaces to form biofilms. Pseudomonas microcolonies growing in a biofilm on a catheter  Biofilms and Microbial Associations Complex relationships among numerous microorganisms ◦ Form on surfaces, medical devices, mucous membranes of digestive system ◦ Form as a result of quorum sensing 1 Free-swimming microbes are vulnerable to environmental Water flow stresses. Chemical structure of one type of quorum-sensing molecule Water channel Escaping Bacteria microbes Matrix 2 3 The cells begin producing 4 Quorum sensing 5 New cells arrive, 6 Some microbes escape Some microbes land an intracellular matrix and triggers cells to possibly including new from the biofilm to resume on a surface, such as secrete quorum-sensing change their species, and water a free-living existence a tooth, and attach. molecules. biochemistry and channels form in the and, perhaps, to form a shape. biofilm. new biofilm on another surface.  Biofilms  Many harmful microbes may be present in biofilms http://www.clspectrum.com/issues/2008/january-2008/cultivating-  Examples include dental plaque, rocks in streams, soap compliance scum on shower curtains, and even films on contact lenses and contact lens storage cases  Studies have shown that contamination of lens cases by bacteria, fungi, and amoebae is common with 20% to 80% of lens wearers having a contaminated lens case.  Biofilms have been shown to display increased resistance to antibiotic treatment Scientists seeking ways to prevent biofilm formation Examples of Biofilms in Health and Medicine :http://www.erc.montana.edu/CBEssentials-SW/bf-basics-99/bbasics- 01.htm http://www.whoi.edu/cms/images/oceanus/2_82430.jpg Biofilm on the tooth of a patient with periodontitis – there are multiple bacteria that are piled on top of each other. http://www.hopkinsarthritis.org/physician-corner/rheumatology-rounds/round-34-periodontal-disease-and-rheumatoid-arthritis/ Figure 3.11 Biofilms.  Tell Me Why? ◦ Why should cardiac nurses and respiratory therapists care about biofilms? Prokaryotic Cells: Fimbriae ◦ Sticky, bristle like projections ◦ Used by bacteria to adhere to one another, to hosts, and to substances in environment Flagellum ◦ Shorter than flagella ◦ May be hundreds per cell ◦ Along with glycocalyces, serve an important function in biofilms Fimbriae  External Structures of Prokaryotic Cells Pili ◦Special type of fimbriae ◦Also known as conjugation pili ◦Longer than fimbriae but shorter than flagella ◦Bacteria typically have only one or two per cell. ◦Transfer DNA from one cell to another (conjugation) Figure 3.12 Pili. Other Important Structures  Endospores Produced by Gram-positive Bacillus and Clostridium bacteria Are very durable and have a high potential for pathogenicity Constitutes a defensive strategy against hostile or unfavorable conditions Serious concern to food processors, health care professionals, and governments Are stable resting stages that barely metabolize and germinate only when conditions improve ◦ Are NOT considered a reproductive stage ◦ Each vegetative cell transforms into one endospore ◦ Each endospore germinates to form one vegetative cell Figure 3.24: Sporulation: The formation of an endospore Cytoplasmic Cell wall membrane DNA is replicated. A cortex of calcium and dipicolinic acid is Cortex DNA deposited between the membranes. Vegetative cell Spore coat forms Spore coat DNA aligns along around endospore. the cell’s long axis. Outer Endospore matures: spore coat Cytoplasmic membrane Forespore completion of spore coat invaginates to form and increase in resistance forespore. to heat and chemicals by unknown process. Endospore Outer Endospore is released from spore coat original cell. Cytoplasmic membrane First grows and engulfs membrane forespore within a second membrane. Vegetative cell’s DNA disintegrates. Second membrane ***This is an 8 to 10 Hour process Prokaryotic Flagella Function: Structure: Are responsible for movement Composed of filament, hook, and basal body Have long structures that extend beyond cell Flagellin protein (filament) deposited in a helix surface at the lengthening tip Are not present on all prokaryotes Base of filament inserts into hook Most of the cocci Basal body anchors filament and hook to cell (e.g. Staphylococci, Streptococci etc) don’t wall by a rod and a series of either two or four have flagella so they are non-motile. rings of integral proteins Gram Positive & Gram Negative Bacteria Flagella [ I N SE R T F I G U R E 3. 6] External Structures of Prokaryotic Cells Prokaryotic Flagella: Movement ◦ Precise mechanism by which bacterial flagella move is not completely understood ◦ Rotate 360° like the shaft of a motor; rotation propels bacterium through environment ◦ May rotate at more than 100,000 rpm and is reversible (changes direction from clockwise to counterclockwise).  Prokaryotic Flagella: Movement ◦ Bacteria move with a series of “runs” Tumbles occur when flagella rotate punctuated by “tumbles” clockwise and become “unbundled” ◦ Runs – produced by counterclockwise rotations; occurs in a single direction for a period of time ◦ Tumbles – are abrupt, random changes in direction resulting from clockwise rotations Runs occur when flagella rotate Example of counterclockwise and become “bundled” positive chemotaxis Figure 3.9 Motion of a peritrichous bacterium Attractant Run Tumble Bacteria move in response to a stimulus (taxis) Stimulus may be either light (phototaxis) or a chemical (chemotaxis). Run Tumble  Clinical Significance Role in Pathogenesis: Escherichia coli and Proteus species are common causes of Urinary tract infections. The flagella of these bacteria help the bacteria by propelling up the urethra into the bladder. Role in Identification: Some species of bacteria, eg. Salmonella species are identified in the clinical laboratory by the use of Specific antibodies against flagellar proteins.  Prokaryotic Cytoplasmic Membranes Function ◦ Energy storage ◦ Harvest light energy in photosynthetic prokaryotes ◦ Selectively permeable ◦ Naturally impermeable to most substances ◦ Proteins allow substances to cross membrane ◦ Occurs by passive or active processes ◦ Maintain concentration and electrical gradient Figure 3.17 Electrical potential of a cytoplasmic membrane. Na+ Cl– Cell exterior (extracellular fluid) –30 mV Cytoplasmic membrane Integral protein Protein DNA Protein Cell interior (cytoplasm)  Prokaryotic Cytoplasmic Membranes Function ◦Passive processes ◦Diffusion ◦Facilitated diffusion ◦Osmosis ◦Isotonic solution ◦Hypertonic solution ◦Hypotonic solution Prokaryotic Cytoplasmic Membranes [INSERT FIGURE 3.17] Figure 3.21 Mechanisms of active transport. Extracellular fluid Uniport Cytoplasmic membrane ATP ATP ADP P ADP P Symport Cytoplasm Uniport Antiport Coupled transport: uniport and symport Figure 3.20 Effects of isotonic, hypertonic, and hypotonic solutions on cells. Cells without a wall (e.g., mycoplasmas, H2O H2O animal cells) H2O Cell wall Cell wall Cells with a wall H2O H2O H2O (e.g., plants, fungal and bacterial cells) Cell membrane Cell membrane Isotonic Hypertonic Hypotonic solution solution solution Figure 3.22 Group translocation. Group translocation: Substance is chemically modified during transport  Prokaryotic Structures Cytosol – liquid portion of cytoplasm Inclusions – may include reserve deposits of chemicals Nonmembranous Organelles ◦ Ribosomes – sites of protein synthesis ◦ Cytoskeleton – plays a role in forming the cell’s basic shape Figure 3.23 Inclusion Granules of PHB in the bacterium Azotobacter chroococcum Polyhydroxybutyrate Archaea bacteria Extremophile bacteria; Require extreme conditions of temperature, pH, and/or salinity to survive Reproduce by binary fission, budding, or fragmentation Most are cocci, bacilli, or spiral forms; pleomorphic forms exist Not known to cause disease in humans Prominent members are thermophiles and halophiles  Thermophiles ◦ DNA, RNA, cytoplasmic membranes, and proteins do not function properly below 45°C ◦ Hyperthermophiles require temperatures over 80°C ◦ Two representative genera: ◦ Thermococcus ◦ Pyrodictium Figure 11.12 Some hyperthermophilic archaea live in hot springs.  Halophiles ◦ Inhabit extremely saline habitats ◦ Depend on greater than 9% NaCl to maintain integrity of cell walls ◦ Many contain red or orange pigments ◦ May protect from sunlight ◦ Most studied—Halobacterium salinarium Figure 11.13 The habitat of halophiles: highly saline water. Methanogens ◦ Largest group of archaea ◦ Convert carbon dioxide, hydrogen gas, and organic acids to methane gas ◦ Convert organic wastes in pond, lake, and ocean sediments to methane ◦ Some live in colons of animals ◦ One of primary sources of environmental methane ◦ Have produced ~10 trillion tons of methane that is buried in mud on ocean floor  Archaea Bacteria - Archaeal Cell Walls ◦ Do not have peptidoglycan in their cell walls ◦ Contains variety of specialized polysaccharides and proteins ◦ Gram-positive archaea stain purple ◦ Gram-negative archaea stain pink - All archaea have cytoplasmic membranes ◦ Maintain electrical and chemical gradients ◦ Control import and export of substances from the cell External Structures of Archaea Glycocalyces ◦ Function in the formation of biofilms ◦ Adhere cells to one another and inanimate objects Flagella ◦ Consist of basal body, hook, and filament ◦ Numerous differences with bacterial flagella Fimbriae and Hami ◦ Many archaea have fimbriae ◦ Some make fimbriae-like structures called hami ◦ Function to attach archaea to surfaces © 2012 Pearson Education Inc. Hamus Grappling hook Prickles  Cytoplasm of Archaea – Archaeal cytoplasm similar to bacterial cytoplasm ◦ Have 70S ribosomes ◦ Fibrous cytoskeleton ◦ Circular DNA – Archaeal cytoplasm also differs from bacterial cytoplasm ◦ Different ribosomal proteins ◦ Different metabolic enzymes to make RNA ◦ Genetic code more similar to eukaryotes © 2012 Pearson Education Inc. Figure 3.27 Representative shapes of archaea-overview Table 3.3 Some Structural Characteristics of Prokaryotes