Microbiology - BIO210: Cell Structure and Function PDF

CH3 Microbiology – BIO210 Cell structure and function Outline: By the end of this lecture, you should be able to: ❖Characteristics of Cells & Life ❖Structure of Bacteria ❖Classification of Bacteria  Characteristics of Cells and Life All living things (single and...

CH3 Microbiology – BIO210 Cell structure and function Outline: By the end of this lecture, you should be able to: ❖Characteristics of Cells & Life ❖Structure of Bacteria ❖Classification of Bacteria  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 Eukaryotic cells: Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display animals, plants, fungi, and protists Prokaryotic Eukaryotic Nucleus Mitochondria Chromosome – Contain membrane-bound organelles Ribosomes Ribosomes that compartmentalize the cytoplasm and perform specific functions – Contain double-membrane bound nucleus with DNA chromosomes Cell wall Cell membrane Prokaryotic cells: Flagellum Flagellum Cell membrane bacteria and archaea – No nucleus or other membrane-bound organelles  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 *  Structure of a bacterial cell Fimbriae Ribosomes Cell wall Cell membrane Capsule Slime layer Cytoplasmic matrix Mesosome Actin filaments Chromosome(DNA) Flagellum Pilus Inclusion body Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  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 3 parts: 1. Filament – a long, thin, helical Filament structure composed of the protein flagellin Hook Outer 2. Hook – curved sheath membrane L ring Cell wall 3. Basal body – a stack of rings Basal body Rod Rings Periplasmic space Rings firmly anchored in cell wall Cell membrane (a) 22 nm (b) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Flagella (a) (c) Rotates 360o Functions in the motility of a cell through the environment (b) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 * *  Flagellar Responses Guide bacteria in a direction in response Key to external stimulus: Chemical stimuli – chemotaxis; positive Tumble (T) Run (R) Tumble (T) and negative Light stimuli – phototaxis T T T T Signal sets flagella into motion clockwise R or counterclockwise: R Counterclockwise – results in smooth linear direction – run (a) No attractant or repellent (b) Gradient of attractant concentration Clockwise – tumbles Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Periplasmic Flagella PF PC OS Internal flagella, enclosed in (a) the space between the outer sheath and the cell wall Outer sheath (OS) peptidoglycan Protoplasmic cylinder (PC) Produce cellular motility by Periplasmic flagella (PF) Peptidoglycan contracting and imparting twisting or flexing motion (b) Cell membrane Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Fimbriae Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fine, proteinaceous, hairlike bristles emerging from the cell surface Function in adhesion to other (a) © Eye of Science/Photo Researchers, Inc. E. coli cells cells and surfaces Intestinal microvilli (b) * Dr. S. Knutton from D.R. Lloyd and S. Knutton, Infection and Immunity, January 1987, p 86-92. © ASM  Pili Fimbriae Pili Rigid tubular structure made of pilin protein Found mostly in gram-negative cells Function to join bacterial cells for partial DNA transfer called conjugation Sometimes adherence, movement © L. Caro/SPL/Photo Researchers, Inc. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Some differences between Fimbriae and Pili S.N. Characteristics Fimbriae Pili Fimbriae are tiny bristle-like fibers arising Pili are hair like microfibers that are thick 1 Definition from the surface of bacterial cells. tubular structure made up of pilin. 2 Length Shorter than pili Longer than fimbriae. 3 Diameter Thin Thicker than fimbriae. 4 Number No. of fimbriae are 200-400 per cell. No of pili are less 1-10 per cell. 5 Made up of Fimbrillin protein. Pilin protein. 6 Rigidity Less rigid. More rigid than fimbriae. Both gram positive and gram-negative 7 Found in Only gram-negative bacteria. bacteria. Is governed by bacterial genes in the nucleoid 8 Formation Is governed by plasmid genes. region. Responsible for cell-to-surface attachment. Responsible for bacterial conjugation. 9 Function Specialized for attachment i.e enable the cell Two basic function of pili. They are gene to adhere to the surfaces of other bacteria. transfer and attachment. Type IV pili shows twitching type of 10 Motility Do not function in active motility. motility.  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 Slime layer Capsule (a) (b) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Functions of the Glycocalyx Protect cells from dehydration and nutrient loss Inhibit killing by white blood cells by phagocytosis, contributing to pathogenicity Attachment - formation of biofilms Colony without a capsule Colonies with a capsule Cell body Capsule © Kathy Park Talaro © John D. Cunningham/Visuals Unlimited (a) (b)  Biofilm on a catheter Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Catheter surface Fungal cells Staphylococci Janice Carr/CDC  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  Structure of Cell Walls (a) The peptidoglycan of a cell wall is a huge, 3-dimensional lattice work that is actually one giant molecule to surround and support the cell. Determines cell shape, and prevents lysis due to changing osmotic pressures (b) This shows the molecular pattern of peptidoglycan. It has alternating glycans (NAG and NAM) bound together in long strands. The NAG stands for N-acetyl glucosamine, and the NAM stands for N- Peptidoglycan is the primary component: acetyl muramic acid. Adjacent muramic acid molecules on parallel chains are bound by a cross-linkage of peptides (green spheres) – Unique macromolecule composed of a CH2OH O CH2OH O repeating framework of long glycan NAG O O NAM O NAG NAG O O NAM O NAG chains cross-linked by short peptide H3 C C C H NH C O H3 C C C H NH C O (c) An enlarged view of the links between the NAM molecules. fragments CH3 CH3 Tetrapeptide chains branching off the muramic acids connect by L–alanine amino acid Interbridges. The D–glutamate amino acids in the interbridge can L–alanine vary or may be lacking entirely. It L–lysine is this linkage that provides rigid D–glutamate D–alanine yet flexible support to the cell. L–lysine –glycine –glycine –glycine D–alanine –glycine –glycine Interbridge  Gram-Positive Cell Wall – 20-80 nm thick peptidoglycan Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. – Includes teichoic acid and lipoteichoic Peptidoglycan acid: function in cell wall maintenance and Cell membrane enlargement during cell division; move cations across the cell envelope; stimulate a specific immune response Gram (+) – Some cells have a periplasmic space, between the cell membrane and the cell wall Cell membrane Cell wall (peptidoglycan) © S.C Holt/Biological Photo Service  Gram-Negative Cell Wall Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. – Inner and outer membranes and periplasmic space between them contains a thin peptidoglycan layer Cell membrane – Outer membrane contains Peptidoglycan lipopolysaccharides (LPS) Outer membrane Lipid portion (endotoxin) may become Gram (–) 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 Cell membrane Periplasmic space Peptidoglycan Cell wall Outer membrane © T. J. Beveridge/Biological Photo Service Structures of Gram-Positive and Gram-Negative Bacterial Cell Walls Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lipoteichoic acid Wall Lipopolysaccharides Porin proteins Phospholipids Teichoic acid Outer membrane layer Peptidoglycan Envelope Periplasmic space Cell membrane Lipoproteins Membrane proteins Periplasmic space Membrane protein Phospholipid Porin Peptidoglycan Membrane Lipoprotein proteins Teichoic acid Lipopolysaccharide * Comparison of Gram-Positive and Gram-Negative Cell Walls  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 *  The Gram Stain Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Microscopic Appearance of Cell Chemical Reaction in Cell Gram (+) Gram (–) Gram (+) Gram (–) Step 1 Crystal Violet (primary Both cell walls stain with the dye. dye) 2 Gram’ siodine Dye crystals No effect (mordant) trapped in cell of iodine 3 Alcohol (decolorizer) Crystals remain Outer wall is in cell. weakened; cell loses dye. 4 Safranin (red dye counterstain) Red dye Red dye stains has no effect. the colorless cell.  Nontypical Cell Walls (always some exceptions) 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 *  Cell Membrane Structure Carbohydrate receptor Glycolipid Phospholipid bilayer with a mosaic of Integral Integral embedded proteins – fluid mosaic model protein protein Functions in: – Providing site for energy reactions, nutrient processing, and synthesis – Passage of nutrients into the cell and discharge of wastes – Cell membrane is selectively permeable Phospholipid Peripheral protein Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Inside the Bacterial Cell Cell cytoplasm: – Dense gelatinous solution of sugars, amino acids, and salts – 70-80% water (Why is this important to know?) Serves as solvent for materials used in all cell functions *  Nucleoid Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chromosome – Single, circular, double-stranded DNA molecule that contains all the genetic information required by a cell Plasmids – Free small circular, double-stranded DNA – Not essential to bacterial growth and metabolism – Used in genetic engineering - readily manipulated and transferred from cell to cell Courtesy of Michael J. Daly  Bacterial Ribosome Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Ribosome (70S) proteins – Site of protein synthesis – Found in all cells Large subunit Small subunit (50S) (30S) *  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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. MP © D. Balkwill and D. Maratea (a) (b)  Bacterial Internal Structures Actin filaments Cytoskeleton – Many bacteria possess an internal network of protein polymers that is closely associated with the cell wall Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  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 *  Sporulation cycle Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 Vegetative cell Chromosome Cell wall Cell membrane 2 9 Germination Chromosome is spore swells duplicated and and releases separated. vegetative cell. 8 Sporulation Cycle 3 Free spore is Exosporium released with Spore coat Cell is separated the loss of the Cortex into a sporangium sporangium. Forespore and forespore. Core Sporangium 7 4 Exosporium Mature endospore Sporangium engulfs Core forespore for further development. Spore coats Cortex 5 6 Cortex and Sporangium begins outer coat layers to actively synthesize are deposited. spore layers around SJ Jones, CJ Paredes, B Tracy, N Cheng, R Sillers, RS Senger, forespore. ET Papoutsakis, "The transcriptional program underlying the physiology of clostridial sporulation," Genome Cortex Early spore Biol., 2008. 9:R114  Endospores Dehydrated, metabolically inactive Thick coat Longevity verges on immortality, 250 million years Resistant to ordinary cleaning methods and boiling Pressurized steam at 120oC for 20-30 minutes will destroy  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  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Common bacterial shapes (a) (b) (c) Coccus Rod/Bacillus Vibrio From Jacob S. Teppema, “In vivo adherence and colonization of Vibrio cholerae Janice Janice strains that differ in hemagglutinating activity and motility, ” Journal of Infection and Carr/CDC Carr/CDC Immunity, 55(9): 2093-2102, Sept. 1987. Reprinted by permission of American Society for Microbiology (d) (e) (f) Branching Spirillum Spirochete filaments Photo by De Wood. Digital colorization by Chris © VEM/Photo Researchers, © Science VU/Frederick Mertz/Visuals Pooley Inc. Unlimited Key to Micrographs (a) Micrococcus luteus (22,000×) (b) Legionella pneumophila (6500×) (c) Vibrio cholerae (13,000×) (d) Aquaspirillum (7,500×) (e) Spirochetes on a filter (14,000×) (f) Streptomyces species (6500×)  Pleomorphism © A.M. Siegelman/Visuals Unlimited Metachromatic granules Variation in cell shape and size within a single species – often occurs in response to the environment Palisades arrangement Some species are noted for their pleomorphism Metachromatic granules Palisades arrangement Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Bacterial Arrangements (a) Division in Diplococci Streptococci (variable one plane (two cells) number of cocci in chains) Arrangement of cells is dependent on pattern of division and how cells remain attached after division: – Cocci: (b) Division in two perpendicular planes Tetrad (cocci in packets of four) Sarcina (packet of 8 – 64 cells) Singles Diplococci – in pairs Tetrads – groups of four Irregular clusters Chains (c) Division in Irregular clusters (number of cells Cubical packets (sarcina) several planes varies) – Bacilli: Diplobacilli Chains Staphylococci and Micrococci Palisades Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Classification Systems for Prokaryotes 1. Microscopic morphology – individual cell appearance 2. Macroscopic morphology – colony appearance 3. Bacterial physiology – presence of products that are the result of bacterial metabolism and physiological activities 4. Serological analysis – basically antibody binding properties (antibody is a large molecule produced by the body to attack foreign agents) 5. Genetic and molecular analysis – identification based on the presence of genetic materials or molecules  Bacterial Taxonomy Based on Bergey’s Manual Bergey’s Manual of Determinative Bacteriology – 5 volume resource covering all known prokaryotes – Classification based on genetic information –phylogenetic – Two domains: Archaea and Bacteria – Five major subgroups with 25 different phyla Bergey’s Classification Scheme  Diagnostic Scheme for Medical Use Uses phenotypic qualities in identification – Restricted to bacterial disease agents – Divides bacteria based on cell wall structure, shape, arrangement, and physiological traits  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 Free-living nonpathogenic bacteria Photosynthetic bacteria – use photosynthesis, can synthesize required nutrients from inorganic compounds – Cyanobacteria (blue-green algae) – Green and purple sulfur bacteria – Gliding, fruiting bacteria – Carry out more photosynthesis than all plants combined *  Unusual Forms of Medically Significant Bacteria Rickettsial cells Obligate intracellular parasites – Rickettsias Very tiny, gram-negative bacteria Most are pathogens Nucleus Obligate intracellular pathogens Cannot survive or multiply outside of a host cell Rickettsia rickettisii – Rocky Mountain spotted fever Baca and Paretsky, Microbiological Reviews, 47(20);133, fig. 16, June 1983 © ASM Vacuole Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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