Micro - Chapter 4 PDF

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Microbio Chapter 4 Notes...

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Chapter Four – Functional Anatomy of Prokaryotic and Eukaryotic Cells Comparing Prokaryotic and Eukaryotic Cells: An Overview 

Prokaryotes and eukaryotes are chemically similar – both contain nucleic acid, proteins, lipids, carbohydrates o Same kinds of chemical reactions to metabolize food, build proteins, store energy

Prokaryotes

Eukaryotes

DNA not enclosed within membrane Usually a singular circularly arrange chromosome

DNA is found in cell’s nucleus which is separated from cytoplasm by a nuclear membrane and the DNA is found in multiple chromosomes DNA is consistently associated with chromosomal proteins called histones and with nonhistones Have a number of membrane-enclosed organelles (mitochondria, endoplasmic reticulum, Golgi complex, lysosomes, and sometimes chloroplasts Their cell walls, when present, are chemically simple Cell division usually involves mitosis – chromosomes replicate and an identical set is distributed into each of the two nuclei – process is guided by mitotic spindle – division of cytoplasm and other organelles follows – two cells produced are identical

DNA not associated with histones Other proteins are associated with DNA Lack membrane-enclosed organelles

Cell walls almost always contain the complex polysaccharide peptidoglycan Usually divide by binary fission. During this process, DNA is copied, and cell splits into two cells Binary fission involves fewer structures and processes than eukaryotic cell division

THE PROKARYOTIC CELL

The Size, Shape, and Arrangement of Bacterial Cells 

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Members of prokaryotic world make up vast heterogeneous group of very small unicellular organisms o Include: bacteria (majority) and archaea  About 99% of bacteria in nature exists in biofilms Bacteria comes in many sizes and shapes: o Coccus: spherical  Cocci that remain in pairs after dividing = diplococcic  When they divide and remain in chains = streptococci  Those that divide in two planes and remain in groups of four = tetrads  Those that divide in three planes and remain attached in cube like groups of eight = sarcine  Those that divide in multiple planes and form grape like clusters or broad sheets = staphylococci o Bacillus: rod-shaped  Most appear as single rods  Diplobacilli, streptobacilli  Coccobacilli = so oval shaped that they look like cocci o Spiral  Vibrios = curved rods  Spirilla = helical shape (like a corkscrew and fairly rigid bodies)

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 Spirochetes = helical and flexible Shape of bacteria is determines by heredity Most bacteria are monomorphic – maintain a single shape Environmental conditions can alter shape – if shape is altered, identification is difficult Some are pleomorphic – can have many shapes

Structures External to the Cell Wall Glycocalyx  Glycocalyx: sugar coat (substances that surround cells) – many prokaryotes secrete glycocalyx on surface  Bacterial glycocalyx – viscous (sticky) gelatinous polymer that is external to cell wall and composed of polysaccharide, polypeptide, or both  For the most part, it is made inside the cell and secreted to the cell’s surface  Capsule: substance is organized and is firmly attached to the cell wall o Presence of capsule can be determined by negative staining o Important in contributing to bacterial virulence – degree to which pathogen causes disease o Protect pathogenic bacteria from phagocytosis by cells of the host  Slime layer: substance is unorganized and only loosely attached to the cell wall  Very important component of biofilms o Glycocalyx that helps cells in biofilm attach to their target environment and to each other = extracellular polymeric substance (EPS)  Protects cells within it, facilitates communication among them, and enables cells to survive by attaching to various surfaces in natural environment  Attachment allows bacteria to grow on diverse surfaces (rocks, plant roots, human teeth)  Protect a cell against dehydration – its viscosity may inhibit the movement of nutrients out of the cell Flagella  Flagella: long filamentous appendages that propel bacteria  Atrichous: bacteria that lack flagella (without projections)  Flagella can be: o Peritrichous: distributed over the entire cell o Polar: at one or both poles or ends of the cell  Monotrichous: a single-flagellum at one pole  Lophotrichous: a tuft of flagella coming from one pole  Amphitrichouse: flagella at both poles of the cell  Three basic parts: o Filament: long outermost region – constant in diameter and contains globular (roughly spherical) protein flagellin arranged in several chains that intertwine and form a helix around a hollow core  In most bacteria, filament are not covered by a membrane or sheath o Hook: filament is attached to a slightly wider hook – consists of different protein o Basal body: anchors the flagellum to the cell wall and plasma membrane  Composed of small central rod inserted into a series of rings  Semirigid, helical structure – moves cell by rotating from basal body  Can alter speed and direction of rotation of flagella – bacteria are capable of various patterns of motility – ability of an organism to move by itself

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Taxis: movement of bacteria toward or away from a particular stimulus o Chemotaxis (chemicals) and phototaxis (light) H antigen: flagellar protein – useful for distinguishing among serovars – variations within a species – of gram-negative bacteria

Axial Filaments  Axial filaments (endoflagella): bundles of fibrils that arise at the ends of the cell beneath an outer sheath and spiral around the cell o Axial filaments anchored at one end of the spirochetes (group of bacteria with unique structure and motility) have structure similar to flagella Fimbriae and Pili  Many gram-negative bacteria have hairlike appendages that are shorter, straighter, and thinner than flagella – used for attachment and transfer of DNA (not motility) – structures are arranged helically around a central core o Divided into two groups – fimbriae and pili  Fimbriae: can occur at poles of the bacterial cell or can be evenly distributed over the entire surface of the cell o A few to several hundred per cell o Tendency to stick to each other and to surfaces o Involved in forming biofilms and other aggregations on surfaces of liquids, glass and rocks o When fimbriae are absent, colonization cannot happen and no diseases ensues  Pili: usually longer than fimbriae – only one or two per cell o Involved in motility and DNA transfer o Twitching motility: pilus makes contact with surface then retracts (powerstroke) o Gliding motility: smooth gliding movement of myxobacteria  Provides means for microbes to travel in environments with a low water content (biofilms and soil) o Conjugation (sex) pili – pili used to bring bacteria together, allowing the transfer of DNA from one cell to another

The Cell Wall 

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Cell wall: complex, semirigid structure responsible for the shape of the cell o Surrounds the underlying, fragile plasmsa (cytoplasmic) membrane and protects it and interior of the cell from adverse changes in the outside environment o Almost all prokaryotes have cell walls Major function = prevent bacterial cells from rupturing when water pressure inside cell is greater than outside the cell o Helps maintain shape of bacterium and serves as a point of anchorage for flagella o As volume of a bacterial cell increases – plasma membrane and cell wall extend as needed Contributes to ability of some species to cause disease and is site of action of some antibiotics Chemical components is used to differentiate major types of bacteria

Composition and Characteristics  Bacterial cell wall composed of macromolecular network – peptidoglycan (murein) – present either alone or in combination with other substances

Consists of repeating disaccharide attached by polypeptides to form lattice that surrounds and protects entire cell o Disaccharide portion made up of monosaccharides – N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) – which are related to glucose  Various components of peptidoglycan are assembled in the cell wall  Alternating NAM and NAG molecules are linked in rows of 10-65 sugars to form a carbohydrate “backbone”  Adjacent rows are linked by polypeptides (peptide portion of peptidoglycan)  Structure of polypeptide links always includes tetrapeptide side chains – four amino acids attached to NAMs in the backbone  Parallel tetrapeptide side chains may be directly bonded to each other or linked by a peptide cross-bridge – consists of a short chain of amino acids  Penicillin interferes with final linking of peptidoglycan rows by peptide crossbridges  Result: cell wall weakens and cell undergoes lysis – destruction caused by rupture of the plasma membrane and the loss of cytoplasm Gram-Positive Cell Walls o Cell wall consists of many layers of peptidoglycan, forming a thick, rigid structure  Gram-negative cell walls contain only a thin layer o Contain teichoic acids which consists mainly of an alcohol (like glycerol or ribitol) and phosphate  Two classes of teichoic acids:  Lipoteichoic acid – spans the peptidoglycan layer and is linked to plasma membrane  Wall teichoic acid – linked to peptidoglycan layer  Teichoic acids (negative charge from phosphate group) may bind and regulate movement of cations (positive) into and out of cell  Assume a role in cell growth – prevents extensive wall breakdown and possible cell lysis  Provide much of wall’s antigenic specificity – make it possible to identify gram-positive bacteria by lab tests o Cell walls of gram-positive streptococci are covered with various polysaccharides – allow them to grouped into medically significant types Gram-Negative Cell Walls o Consist of one or a very few layers of peptidoglycan and an outer membrane o Peptidoglycan is bonded to lipoproteins (lipids covalently linked to proteins) in outer membrane and is in the periplasm – gel-like fluid between outer membrane and plasma membrane  Periplasm contains high concentration of degradative enzymes and transport proteins o Do not have teichoic acid o More susceptible to mechanical breakage (only have small amount of peptidoglycan) o Outer membrane:  Consists of lipopolysaccharides (LPS), lipoproteins, and phospholipids  Strong negative charge helps evade phagocytosis and actions of complement (lyses cells and promotes phagocytosis) o

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Provides barrier to certain antibiotics (penicillin), digestive enzymes (Lysozyme, detergents, heavy metals) Does not provide barrier to all substances in environment because nutrients must pass through to sustain metabolism of cell Part of permeability is because of porins – proteins in the membrane (form channels)  Porins let molecules like nucleotides, disaccharides, peptides, amino acids, vitamin B12, and iron pass through LPS – large complex molecule that contains lipids and carbohydrates and consists of:  Lipid A o Lipid portion of LPS – embedded in top layer o When gram-negative bacteria die, they release lipid A – functions as an endotoxin o Responsible for symptoms associated with infections by gramnegative bacteria  Core polysaccharide o Attached to lipid A – contains unusual sugars o Role = structural – provide stability  O polysaccharide o Extends out from core polysaccharide and made up of sugar molecules o Function = antigen – helps distinguish species of gram-negative bacteria (comparable to teichoic acids in gram-positive cells)

Cell Walls and the Gram Stain Mechanism  Mechanism based on differences in structure of cell walls of gram-negative and positive bacteria and how each react to various reagents  Crystal violet – stains both positive and negative  When iodine (mordant) is applied, it forms large crystals that are too large to escape cell wall  Application of alcohol: o Dehydrates peptidoglycan of gram-positive cell – more impermeable to crystal violet o Dissolves outer membrane of gram-negative cell – leaves small holes in peptidoglycan layer – crystal violet iodine diffuses out  Colorless after alcohol wash  When safranin added, cells turn pink Atypical Cell Walls  Some cells have no cell walls or very little wall material o Mycoplasma – smallest known bacteria that can grow and reproduce outside living host cell  Plasma membrane have lipids called sterols – thought to help protect from lysis o Archaea – may lack walls or have walls composed of polysaccharide and proteins but not peptidoglycan  Walls have pseudomurein – substance similar to peptidoglycan  Pseudomurein: contains N-acetylalosaminuronic acid instead of NAM and lacks D-amino acid (found in bacteria cell walls)  Generally cannot be gram-stained

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Acid-fast cell walls o Mycolic acid: hydrophobic waxy lipid – prevents uptake of dyes – forms a layer outside of a thin layer of peptidoglycan  Mycolic acid and peptidoglycan held together by polysaccharide

Damage to the Cell Wall  Exposure to lysozyme o Catalyzes hydrolysis of bonds between sugars in repeating disaccharide backbone of peptidoglycan – causes lysis  Protoplast: wall-less cell  Some can lose cell wall and swell into irregular shapes – L form  Sphereoplast: cellular contents, plasma membrane, and remaining outer wall layer (lysozyme applied to gram-negative instead of positive) o Affects gram-positive more than negative The Plasma (Cytoplasmic) Membrane  Plasma (cytoplasmic) membrane – inner membrane – tin structure lying inside cell wall and enclosing the cytoplasm of the cell  Plasma membrane consists primarily of phospholipids (most abundant chemicals in the membrane) and proteins  Lack sterol – less rigid than eukaryotic membranes  Structure: o Plasma membrane look like two-layered structures o Phospholipid molecules arranged in two parallel rows – lipid bilayer o Many of the proteins and some of the lipids on outer surface have carbohydrates attached to them  Proteins attached to carbohydrates = glycoproteins  Lipids attached to carbohydrates = glycolipids  Glycoproteins and glycolipids help protect and lubricate cell and are involved in cell-to-cell interactions  Function: o Most important function – serve as a selective barrier – materials enter and exit cell  Selective permeability: certain molecules and ions pass through membrane, but others cannot  Large molecules (proteins) cannot pass through  Smaller molecules (water, oxygen, carbon dioxide, simple sugars) usually pass through easily  Ions penetrate membrane easily  Substances that dissolve in lipids enter and exit more easily  Movement also depends on transport molecules o Plasma membranes are important to the breakdown of nutrients and production of energy  Contains enzymes that can catalyze chemical reaction that break down nutrients and produce ATP  Chromatophores or thylakoids: infoldings of membrane that extend to cytoplasm where bacteria, pigments, and enzymes are found o Bacterial plasma membranes appear to have one or more irregular folds – mesosomes  Not true cell structures!

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Destruction of the plasma membrane by antimicrobial agents o Polymyxins (antibiotics) disrupt the membrane’s phospholipids – cause leakage of intracellular contents  Cell death

The Movement of Materials across Membranes  Materials move using passive and active processes  Passive process: substances cross membrane from an area of high concentration to an area of low concentration (move with concentration gradient or difference) without any energy (ATP) o High to low  Active processes: cell must use energy (ATP) to move substances from areas of low concentration to areas of high concentration (against concentration gradient) o Low to high  Passive processes include: o Simple diffusion: net movement of molecules/ions from high to low concentration  Movement continues until equilibrium  Relied on to transport small molecules like oxygen and carbon dioxide across membrane o Facilitated diffusion: integral membrane proteins function as channels/carries to facilitate movement of ions or large molecules across membrane  Integral proteins – transporters or permeases o Osmosis: net movement of solvent molecules across selectively permeable membrane  Chief solvent = water  Water passes through by moving through lipid bilayer by using aquaporin – water channels (membrane protein)  Osmotic pressure: pressure required to prevent movement of pure water into solution containing some solutes  Pressure needed to stop flow of water across selectively permeable membrane o Isotonic solution: overall concentration of solutes equals that found inside cell (no net change) o Hypotonic solution outside cell: concentration of solute lower than inside of cell  Lysis – bursting o Hypertonic solution: higher concentration of solutes inside cell than outside  Cells shrink/collapse – plasmolyze  Active processes: o Depends on transporter proteins in plasma membrane o Enables microbes to move substances across membrane at constant rate – even when in short supply o Group translocation: substance is chemically altered during transport across membrane  Once altered and inside cell, plasma membrane is impermeable to it so it remains inside cell  Requires energy supplied by high-energy phosphate compounds (phosphoenolpyruvic acid – PEP) Cytoplasm  Substance inside plasma membrane

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80% water and contains mainly proteins (enzymes), carbohydrates, lipids, inorganic ions, and low-molecular weight compounds Thick, aqueous, semitransparent, elastic

The Nucleoid  Contains a single, long, continuous, frequently circularly arranged thread of DNA (double stranded) – bacterial chromosome  Bacterial chromosomes are not surrounded by nuclear envelope and do not have histones  Chromosome attached to plasma membrane  Proteins in membrane believed to be responsible for replication of DNA and segregation of new chromosomes to daughter cells during division  Plasmids: small usually circular, double stranded DNA molecules o Replicate independently of chromosomal DNA o Associated with plasma membrane proteins o Used for gene manipulation o Can be lost or gained without harming cell Ribosomes  Function as site of protein synthesis  Composed of two subunits – each consist protein and RNA (ribosomal RNA – rRNA)  Some antibiotics work by inhibiting protein synthesis on ribosomes Inclusions  Inclusions: reserve deposits in cytoplasm  Cells can gather nutrients when they are abundant and keep them for when the environment is deficient

Types of Inclusions Metachromatic granules

Polysaccharide granules Lipid inclusions Sulfur granules Carboxysomes Gas vacuoles

Description -Large inclusions -Collectively known as volutin – reserve of inorganic phosphate that can be used in synthesis of ATP -Found in algae, fungi, protozoa, and bacteria -Consists of glycogen and starch -Common lipid-storage material = poly- β -hydroxybutyric acid -Energy reserve -Contain the enzyme ribulose 1,5-diphosphate carboxylase -Maintain buoyancy so cells can remain at depth in water that allow them to receive oxygen, light, and nutrients -Inclusions of iron odxide

Magnetosomes Endospores  Endospores: “resting” cells formed when essential nutrients are depleted  Highly durable dehydrated cells with thick walls and additional layers  Formed internal to bacterial cell membrane  True endospores are found in gram-positive bacteria  Sporulation (sporogenesis): process of endospore formation within a vegetative cell  Endospores can remain dormant for thousands of years  Germination: process when endospore returns to its vegetative state o Triggered by physical or chemical damage to the endospore’s coat...