Microbiology Flashcards with Answers
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Unlock answersMicrobiology |
Study of organisms and "infectious agents" too small to be seen with the human eye |
Early Microscopists |
Robert Hooke Antoni van Leeuwenhoek |
Robert Hooke |
Amateur Microscopist First to coin term "cell" Published findings in Micrographia |
Antoni van Leeuwenhoek |
Dutch Drapery Merchant Used Lens to peer into a drop of lake water: First to see live microbes First to describe bacteria Called organisms "animalcules" |
Compound Microscope |
Occular and Objective Lens |
Theory of Spontaneous Generation |
"Organisms can arise from non-living matter" |
Detractors of Theory of Spontaneous Generation |
Francesco Redi Louis Pasteur John Tyndall |
Francesco Redi |
Demonstrated worms found on rotting meat cames from eggs of flies landing on meat: Proved this by placing rotting meat in jars and covered one jar with fine gauze. Gauze prevented flies from depositing eggs i.e. no eggs - no worms |
Louis Pasteur |
Father of Modern Microbiology Demonstrated that air is filled with microorganisms: Proved by filtering air in cotton plug Swan Necked Flask |
John Tyndall |
discovered endospore: organism that had secondary life form that could endure long periods of boiling Concluded different infusions required different boiling times |
Golden Age of Microbiology |
1854-1914 Time of great interest in study of microorganisms Between 1875-1918 most disease causing bacteria were discovered Work on viruses began Led to initiation of prevention and treatment of disease |
Robert Koch |
Developed science of medical microbiology: first to show that a specific bacterium was cause of specific disease (ex. bacillus anthracis, anthrax) Worked with TB and anthrax Developed procedures for growing bacteria in pure culture medium |
Koch's Principles |
Rules for establishing that a specific organism is the cause of a specific disease: 1. Organism must be isolated from diseased organism in all cases 2. Organism must be grown in pure culture 3. When introduced back into animal model, organism must cause same symptoms as in original illness 4. Organism must be re-isolated in experimental infection in model |
Pure Culture |
Comes from growth of ONE cell |
Three Domains |
Organisms in each domain share certain properties: Eukarya Bacteria (Prokaryotes) Archaea (Prokaryotes) |
Microbes |
Too small to be seen without microscope Two groups: Living (organisms) Non-living (Infectious agents) |
Prokaryotes |
Single Cell Organism Replicate by Binary Fission Genetic material not contained in membrane bound organelle (no nuclear membrane or nucleoid) Bacteria (Eubacteria) and Archaea ("extremophiles") |
Eukaryotes |
Microbes: Fungi Yeast Protozoa Helmenths |
Infectious Agents |
(non-living) Viruses Viroids Prions ~ newest to have been discovered |
Role of Microorganisms |
Microbes have tremendous impact on human existence; they have killed more people than have ever been killed in war Microorganisms have an important role in the production of oxygen and usable nitrogen Microorganisms are decomposers and are responsible for the breakdown of a wide variety of material |
Normal Flora/Comensal |
Estimated 500-1000 species of bacteria reside in and on the human body Bacteria out number cells in the body 10:1; compete with other organisms for food and space Keep disease causing organisms from breaching host defenses Some bacteria and viruses use human body as habitat for multiplication, persistance and transmission |
Microbiology Applications |
Food Production: fermentation of milk to produce yogurt, cheese, buttermilk; beer, wine Bioremediation: use organisms to degrade environmental waste, clean up oil spills, treat radioactive waste |
Past Triumphs |
Viral disease smallpox once a leading killer ~ no cases since 1977 Plague: major killer in history ~ fewer than 100 die worldwide |
Three Largest Causes of Death by Infectious Diseases |
1. HIV 2. Tuberculosis 3. Malaria |
Element |
Substance that consists of a single type of atom 92 Naturally Occuring Elements Four Primary Elements: Carbon Nitrogen Oxygen Hydrogen |
Atom |
Basic unit of all matter Made up of three major components: Protons Neutrons Electrons (spinning in clouds) |
Formation of Molecules |
Atoms are most stable when the outer orbital contains the maximum number of electrons ~ 1st shell: two 2nd, 3rd, etc shell: eight No full outer shell? UNSTABLE. So gain/lose/share electrons to form bonds and achieve a more stable state. Molecules formed when atoms bond together. |
Covalent Bonds |
Strongest type of bond Achieve stability through the sharing of electrons between atoms. Requires significant energy to break, usually in the form of heat. Bonds can be polar or nonpolar. |
Non-polar Covalent Bonds |
Equal attraction for the shared electrons. Bonds formed between identical atoms or between atoms that have similar attraction for electrons. |
Polar Covalent Bonds |
One atom has a greater attraction to the electrons than the other, ie greater electronegativity. This produces a slight charge different within the molecule ie molarity, and a dipole moment is formed. Ex. Water: Hydrogens have a slight positive charge while oxygen has a slight negative charge. |
Ionic Bonds |
Formed by gaining or losing electrons ~ electrons completely leave first atoms and become part of outer orbital of second atom. This loss/gain leads to charged atoms or ions. These charged atoms are attracted to each other and form a bond between ions ie an ionic bond or salt bridge. Approximately 100x weaker than covalent bonds, dissociate in water at room temperature. |
Hydrogen Bonds |
Weak biological bonds, but if you have a lot it will stabilize and hold molecules together firmly, such as in DNA; like numerous stitches in clothing: one stitch vs many. Formed from attraction of positively charged hydrogen atoms to negatively charged atoms or molecules (usually oxygen or nitrogen) Hydrogen bonds hold molecules together, covalent bonds hold atoms together. Constantly being formed and broken at room temperature. |
Water |
Most important molecule Universal Solvent Allow reactions in our body to occur Makes up over 70% of all living organisms by weight Importance of water depends on its unusual bonding properties |
Bonding Properties of Water |
Hydrogen bonds form between positively charged hydrogen of one molecule and negatively charged oxygen of another creating a latice formation. Hydrogen bonding creates a polar molecule; polar nature accounts for the ability to dissolve numerous compounds. Molecules that dissolve in water must contain charged atoms ie hydrophillic molecules. Ex. NaCl ~ dissolves in water forming Na+ and Cl- ions which become surrounded by water and can no longer nond to each other. |
pH |
pH = -log[H+] Measured on a logarithmic scale of 0 to 14 (0 ~ highly acidic, 14 ~ highly basic or alkaline) When H+ and OH- ions are equal in soultion = neutral solution High H+ = acid, High OH- = base |
Macromolecules |
Biological Macromolecules are divided into three classes: Proteins Polysaccharides (carbohydrates) Nucleic Acids **Lipids** Macromolecules are very large. All are considered polymers made up of monomeric subunits connected through covalent bonding. |
Dehydration and Hydrolysis Reactions |
Dehydration Synthesis: joining subunits together by removing water to allow the polymer to grow Hydrolysis: adding water to break bonds between subunits, shrinking the polymer |
Proteins and their Functions |
Constitute over 50% of cell dry weight Made up of amino acid subunits Most versatile, some responsibilities include: Act as enzymes, catalyzing reactions Composition and shape of certain bacterial structures Gene regulation Nutrient procurement Molecules of communication |
Amino Acids |
Proteins are composed of numerous combinations of 20 naturally occuring amino acids Protein shape and ultimately its function depends on the shape of the sequence of amino acids, ie shape determines function. Always linear, in a chain. All amino acids have the following shared features: a carboxyl group (COO-) an amino group (NH2-) a central carbon a side chain or R group (varies in length, this is what differentiates the amino acids) Amino acids are subdivided based on similarities of side chain. |
Peptide Bonds |
Amino acids are held together by peptide bonds ~ a unique type of polar covalent bond. Formed between the interaction of the carboxyl group of one amino acid and the amino group of the following amino acid. Reaction causes the release of water and formation of peptide bond. |
Primary Protein Structure |
Sequence of amino acids connected by peptide bonds In large part determines other protein features "Beads on a string" Chain grows only in one direction |
Secondary Protein Structure |
Primary structure folds into new configuration that results from weak bonds formed between amino acids. Alpha Helix: helical or spiral structure Beta Sheet: pleated structure Stabilized by hydrogen bonds between carbonyl and amide groups along the polypeptide backbone (peptide bonds). |
Tertiary Protein Structure |
Three dimensional structure Two major shapes: Globular Fibrous Becomes a functional protein |
Quarternary Protein Structure |
Multiple polypeptides held together with covalent (disulfide bonds) or weak bonds to held stabilize structure. Sulfhydro groups make these bonds possible. |
Protein Denaturation |
Proteins must have a specific shape to have a proper function. Environmental conditions (high pH, high salt, high temp) can break bonds within the protein, causing shape change. Shape change causes protein to stop functioning, called denaturation. Denaturation can be reversible or irreversible, determined by environment, however, typically will not reverse. Ex. Chicken Egg: heat to denature protein before you eat. |
Carbohydrates |
SUGARS A diverse group of molecules with various sizes Five carbon sugars form subunits of nucleotides Play an important role in all organisms: - Common and important source of food and energy (even for bacteria) - Form part of nucleic acids - Form part of bacterial cell wall Contain carbon, hydrogen and oxygen in 1:2:1 ratio (CH2O) |
Monosaccharide Carbohydrate |
Single Carbohydrate Molecule (simple sugar) Classified by the number of carbons in molecule Most common monosaccharides: 5 Carbon Sugars 6 Carbon Sugars ~ common in biological systems (ex. glucose, mannose, galactose, fructose) |
Disaccharide Carbohydrate |
Produced by joining two monosaccharides through dehydration synthesis ie water is lost Most Common in Nature: Lactose (glucose + galactose) Sucrose (glucose + fructose) Maltose ~ less common (glucose + glucose) (+) represents glycosidic bond
|
Polysaccharide Carbohydrate |
Chains of monosaccharides Cellulose: - most abundant organic molecule on earth - polymer of glucose molecules - principle constituent in plant cell wall - we depend on enzymes of other animals to break down so we can use (termites) Glycogen: - carbohydrate storage molecule of humans, animals and some bacteria - polymer of glucose subunits Dextran: - storage molecule of carbon and energy for some bacteria - polymer of glucose subunits **Oligosaccharide: short chain of carbohydrates, a few monosaccharides** |
Nucleic Acids |
Two Types: - DNA (Deoxyribonucleic Acid) ~ carries genetic code in all cells - RNA ~ decodes sequence of amino acids to produce proteins Subunits of nucleic acids are nucleotides. |
Nucleotides |
;Nucleotides are composed of three units: - Nitrogen containing ring compound, nitrogenous base: ~ purine (adenine and guanine) **AGgies are Pure** ~ pyrimidine (thymine and cytosine) - Five carbon suger molecule, deoxyribose - Phosphate molecule **Minus phosphate group? Nucleoside** |
Nucleotide Phosphodiester Bond |
Nucleotides are joined through covalent bonding; bond created between phosphate of one nucleotide and sugar of the adjacent through dehydration synthesis. Phosphate molecule acts as a bridge between the #3 (3') carbon of one sugar and the #5 (5') carbon of the adjacent. This results in a sugar phosphate backbone. **3' ~ OH group/5' ~ phosphate group**; |
DNA |
Master molecule that determines the specific properties of the cell. In living organisms, is a double stranded helical molecule. Strands are held together by hydrogen bonding between nitrogen bases. Specific pairing between bases:; A-T or T-A G-C or C-G Bases are complementary |
RNA |
Involved in decoding DNA.; Structure is similar to DNA, but differs in a number of ways: - Thymine is replaced by Uracil - The sugar ribose replaces deoxyribose - RNA is generally shorter - exists as single stranded molecule, not double stranded |
Lipids |
Critical component of the cell membrane (membranes act as gatekeepers for the cell determining what enters and leaves the cell). Heterogeneous group of molecules ie made up of different subunits. Its defining feature is that it is insoluble in water (hydrophobic ~ water hydrogen bonds to itself and forms cage around lipid) Smallest of the four macromolecules. Can be divided into two general classes: simple lipids and compound lipids. |
Simple Lipids |
Contain only carbon, hydrogen and oxygen. Most common are called fats: - solid at room temperature - made of glycerol and fatty acids Fatty acids are long hydrocarbon chains plus an acid group (COOH) at the end.; Glycerol is a carbon hydrogen chain with three hydroxyl (OH) groups attached. This allows for the binding of three fatty acids to one glycerol ie triglyceride.; Steroids are also considered simple lipids. They differ from fats in structure and function,;structure consists of four membered ring. Classified as lipid because steroids are insoluble in water. If one of the rings has a hydroxyl (OH) group attached to it, it is classified as a sterol (ex. cholesterol).; |
Fatty Acids |
Two Groups:; Saturated ~ no double bonds, tails packed tightly so solid at room temperature (fats) Unsaturated ~ double bonds, kinks prevent tight packing so liquid at room temperature (oils) Monounsaturated: one double bond Polyunsaturated: more than one double bond |
Compound Lipids |
Contains fatty acids, glycerol and other elements. Phospholipid: most important compound lipid - made up of a phosphate and two fatty acids attached to a glycerol molecule - phosphate head is polar and soluble in water (hydrophilic) - fatty acids are nonpolar and insoluble in water (hydrophobic) |
Phospholipids |
Major component in lipid cell membrane. Membrane is a double or bilayer of phospholipids. Hydrophilic heads orient towards internal and external environments.; Hydrophobic tails orient themselves away from aqueous environment towards each other. Membrane acts as a barrier to the entry and exit of cellular substances.; |
Bright-Field Microscopy |
Light Microscopy: light passes through specimen, then through series of magnifying lenses. Most common and easiest to use is the brightfield microscope.; Important Factors: Magnification; Resolution; Contrast; |
Magnification |
Compound microscope has two magnifying lenses:; Occular lens Objective lens Most bright-field scopes have four magnifications of objective lenses ~ 4x, 10x, 40x and 100x Lenses combine to enlarge objects, magnification is equal to the factor of the occular times the objective.; Bright-field scopes have condenser lens which has no affect on magnification but is used to focus illumination on specimen.; |
Resolution; |
Usefulness of microscope depends on its ability to resolve two objects that are very close together.; Resolving power is defined as the minimum distance existing between two objects where those objects still appear as separate objects. Resolving power determines how much detail can be seen.; Equation: D=.61;/;sin; ;=wavelength of illuminating light ;=refractive index sin;=1.00 Resolution depends on the quality of the lensesand wavelength of illuminating light ie how much light is released from the lens Max resolving power of most bright-field microscopes is 0.2;;m. (This is sufficient to see most bacterial structures, but too low to see viruses) Resolution is enhanced with lenses higher than 100x with the use fo immersion oil. (Oil reduces light refraction by bridging the gap between specimen slide and lens; oil has nearly the same refractive index as glass.; |
Contrast |
Reflects the number of visible shades in a specimen.; Higher contrast achieved for microscopy through specimen staining. ; |
Examples of Light Microscopes that Increase Contrast |
Phase-Contrast Microscope Interference Microscope Dark-Field Microscope Fluorescence Microscope Confocal Scanning Laser Microscope |
Phase-Contrast; |
Amplifies differences between refractive indexes of cells and surrounding medium.; Uses sets of rings and diaphragms to achieve resolution.; |
Interference Scope |
This microscope causes specimen to appear three dimensional, depends on differences in refractive index.; Most frequently used interference scope is Nomarski differential interference contrast.; |
Dark-Field Microscope |
Reverse Image ie specimen appears bright on a dark background, like a photographic negative.; Achieves image through a modified condenser.; |
Fluorescence Microscope |
Used to observe organisms that are naturally fluorescent or are flagged with fluorescent dye.; Fluorescent molecule absorbs ultraviolet light and emits visible light. Image fluoresces on dark background.; |
Fluorchrome |
Molecule that absorbs light at a specific;; and emits light at a different;;. |
Electron Microscope |
Uses electromagnetic lenses, electrons and fluorescent phosphorescent screen to produce image.; Resolution increased 1,000 fold over brightfield microscope to about **.3nm** Magnification increased to 100,000x. Two Types:; - transmission - scanning; ; |
Transmission Electron Microscope (TEM) |
Used to observe fine detail.; Directs beam of electrons at specimen and electrons pass through or scatter at surface.; Shows dark and light areas, darker areas more dense.; Specimen preparation through thin sectioning and freeze fracturing or freeze etching.; |
Scanning Electron Microscope (SEM) |
Used to observe surface detail. Beam of electrons scan surface of specimen which is convered with metal, usually gold.; Electrons are released and reflected into viewing chamber.; Some atomic microscopes capable of seeing single atoms.; |
Dyes and Staining |
Cells are frequently stained to observe organisms. Stains are made of organic salts. Dyes carry (+) or (-) charge on the molecule, and molecule binds to certain cell structures. Dyes divided into basic or acidic based on charge. Basic dyes carry positive charge and bond to cell structures that carry negative charge (commonly stain the cell). Acidic dyes carry positive charge and are repelled by cell structures that carry negative charge (commonly stain the background).; Basic dyes are more commonly used than acidic dyes. Common basic dyes include:; Methylene Blue Crystal Violet; Safranin Malachite Green |
Staining Procedures |
Simple stain uses one basic stain to stain the cell. This allows for increased contrast between cell and background. All cells stained the same color ie no differentiation between cell types. Differential Stains are used to distinguish one bacterial group from another. It uses a series of reagents. Two most common Differential Stains:; Gram Stain; Acid-Fast Stain |
Gram Stain |
Differentiates bacterial cells. Most widely used procedure for staining bacteria. Developed over a century ago by Dr. Hans Christian Gram. Bacteria separated into two major groups: Gram Positive ~ stained purple Gram Negative ~ stained red or pink |
Four Reagents involved in Gram Stain |
Primary Stain: Crystal Violet ~ stains the cell Mordant: Gram's iodine ~ holds primary stain onto cell Decolorizer: usually alcohol ~ removes primary dye from gram negative cell Counter or Secondary Stain: Safranin ~ recolors cells that lose stain through decolorizer |
Acid-fast Stain |
Used to stain organisms that resist conventional staining Used to stain members of genus Mycobacterium: high lipid concentration in cell wall which prevents uptake of dye, and uses heat to facilitate staining. (Once stained, difficult to decolorize) Can be used to presumptive identification in diagnosis of clinical specimens |
Acid-fast Stain Steps |
Primary dye: carbol fuchsin ~ colors acid-fast bacteria red Decolorizer: generally acid alcohol ~ removes stains from non acid-fast bacteria Counter Stain: methylene blue ~ colors non acid-fast bacteria blue |
Special Stains |
Capsule Stain: example of negative stain; allows capsule to stand out around organism (ex. india ink) Endospore Stain: staining enhances endospore; uses heat to facilitate staining Flagella Stain: staining increases diameter of flagella ie makes more visible |
Prokaryote Shape |
Most Common: Coccus (plural=cocci): spherical Bacillus: rod or cylinder shaped Others: Coccobacillus: short round rod Vibrio: curved rod Spirillum: spiral shaped Spirochete: helical shape Pleomorphic: bacteria able to vary shape |
Morphology of Prokaryotic Cells |
Prokaryotic cells may form groupings after cell division ie cells adhere together after cell division for characteristic arrangements. This arrangement depends on plane of division. Division along a single plane may result in pairs or chains of cells. Pairs=diplococci Chains=streptococci Divisions along two or three perpindicular planes form cubical packets ~ ex. Sarcina genus Division along several random planes form clusters ~ ex. staphylococcus Some bacteria live in groups with other bacterial cells, forming multicellular associations. Ex. Myxobacteria: form a swarm of cells, allowing for the release of enzymes which degrade organic material. In the absence of nutrients, cells form fruiting bodies. Other organisms form biofilms ~ secondary architectures that help organisms stick to objects, protect themselves, obtain nutrients and allow for changes in cellular activity. |
Prokaryote Cytoplasm |
Absence of membrane bounded nucleus; genome of prokaryote sometimes referred to as nucleoid. Absence of membrane bounded intracellular organelles Sizes range from 1-10 μm for bacteria |
Cell Envelope of Bacteria |
Cell Membrane: Inner Membrane (both Gr+ and Gr-) Outer Membrane (only Gr-) Cell Wall Periplasmic Space (periplasm; in between inner and outer) ~ only Gr- |
Cytoplasmic Membrane (1) |
Similar to Plasma Membrane Both bacteria and archaea have cytoplasmic membranes, but phospholipid composition differs between two groups. - Delicate thin fluid structure -Surrounds cytoplasm of cell - Defines boundary; provides compartmentalization of cytoplasmic contents - Serves as a semi-permeable barrier; barrier between cell and external environment determining which molecules pass into or out of cell. Structure is a lipid bilayer with embedded proteins composed of two opposing leaflets of phospholipids; each contains a hydrophilic phosphate head and hydrophobic fatty acid tails |
Cytoplasmic Membrane (2) |
Membrane is embedded with more than 200 proteins. Proteins function as receptors and transport gates. Provides mechanism to sense surroundings. Proteins are not stationary, constantly changing position; called a fluid mosaic model. Only a few molecules pass through membrane via simple diffusion; most pass using transport mechanisms that may require carrier proteins and energy. |
Simple Diffusion |
Process by which molecules move freely across cytoplasmic membrane (through lipid bilayer). Water, certain gases (O2 and CO2) and small hydrophobic molecules pass through via simple diffusion is don't need a protein. High concentration to low concentration |
Diffusion Terminology |
Gradient=concentration differences within an area or on either side of a semi-permeable membrane Diffusion=movement of molecules from an area of high concentration to an area of lower concentration. Equilibrium=molecules evenly distributed across barrier Concentration=# particles/volume |
Osmosis |
The ability of water to flow freely across the cytoplasmic membrane through aquaporins. Water flows to equalize solute concentrations inside and outside the cell ie water will move from area of low solute concentration to area of high solute concentration. Water flows across a membrane toward the hypertonic solution. |
Proton Motive Force |
Membrane also the site of energy production. Energy produced through series of embedded proteins. - Electron Transport Chain - Proteins are used in the formation of proton motive force - Energy produced in proton motive force is used to drive other transport mechanisms and synthesize ATP High energy electrons coming from glucose through metabolism force proteins out of cell; them moving against concentration gradient backin into the cell provides energy for cell to do work. Accumulation of protons outside of plasma membrane. Transporters allow protons into cell. Protons either bring in or expel other substances. Protons fall from higher to lower; potential energy from fall can be used to move molecule against concentration gradient. |
Transport Proteins |
Movement of many molecules directed by transport systems. Transport Systems employ highly selective proteins ie can only transport one kind of molecule. Transport Proteins aka permeases or carriers, span the membrane. Most transport;proteins are produced in response to need. Transport systems include facilitated diffusion, active transport and group translocation. |
Facillitated Diffusion |
**Rare in Bacteria** Moves compounds across membrane through transmembrane protein exploiting a concentration gradient ie only moves in one direction. Flow from area of greater concentration to area of lesser concentration; molecules are transported until equilibrium is reached. System can only utilize a concentration gradient, it cannot create one. No energy is required for facillitated diffusion. ; ; |
Active Transport |
Requires specific transmembrane proteins. Moves compounds against a concentration gradient. Requires an expenditure of energy. Two primary mechanisms: Proton Motive Force ATP Binding Cassette System (ABC) |
ATP Binding Casette System (ABC Transport) |
Use binding proteins to scavenge and deliver molecules to transport complex. |
Group Translocation |
Transporter chemically alters the substance as it is transported across the membrane. Ex. Glucose to Glucose 6 Phosphate ;Uptake of molecule does not alter concentration gradient. Phosphotransferase system example of group transport mechanism. - phosphorylates suger molecule during transport; phosphorylation changes molecule and therefore does not change sugar balance across;the;membrane. ; |
General Secretory Pathways |
System of transmembrane proteins that recognize small part of protein called signal sequence. The signal sequence on the preprotein targets it for secretion and is removed during the secretion process. Once outside the cell, the protein folds into its functional shape. Extracellular enzymes degrade macromolecules so that the subunits can then be transported into the cell. Active secretion=molecules chews up mass so bacteria can use it. |
Bacterial Cell Wall |
Rigis Structure Surrounds Cytoplasmic Membrane Determines shape of bacteria Holds cell together Prevents cell from bursting Unique chemical structure (distinguishes Gr+ from Gr-) |
Peptidoglycan (PTG) |
Rigidity of cell wall is due to PTG, a compound found only in bacteria. Basic Structure: Alternating series of two sugers (linked covalently): N-acetylglucosamine (NAG) N-acetylmuramic acid (NAM) Joined subunits form glycan chain held together by string of four amino acids aka tetrapeptide chain |
Gr+ Cell Wall |
Composed of plasma membrane and PTG. Relatively thick layer of PTG, as many as thirty layers. Regardless of thickness, PTG is permeable to numerous substances. Teichoic Acid Component: - gives cell negative charge - Ribitol phosphate or glycerol phosphate |
Gr- Cell Wall |
Only contains a thin layer of PTG. PTG sandwiched between outer membrane and cytoplasmic membrane. Region between outer membrane and cytoplasmic membrane is called periplasm (space in between inner and outer leaflet): - Most secreted proteins contained here - Proteins of ABC transport system located here Gr- Cell Envelope: Plasma Membrane PTG periplasm lipopolysaccharide |
Outer Membrane of Gr- Bacteria |
Constucted of lipid bilayer: - much like cytoplasmic membrane but outer leaflet made of lipopolysaccharides NOT phospholipids - outer membrane also called the lipopolysaccharide layer or LPS layer LPS serves as barrier to a large number of molecules, small molecules or ions pass through channels called porins. Portions of LPS medically significant: - O-specific polysaccharide side chain - **Lipid A (endotoxin)** |
O-specific polysaccharide and Lipid A |
O-specific polysaccharide: - directed away from membrane, interact with outside - opposite location of Lipid A - Used to identify certain species or strains Lipid A: - portion that anchors LPS molecule in lipid bilayer - plays role in recognition of infection - molecule present with Gr- infection of bloodstream |
Cell Wall |
PTG as a target - many antimicrobial agents destroy or interfere with synthesis of PTG Examples include: Penicillin Lysozyme Differences in cell wall account for differences in staining characteristics: - Gr+ bacterium retain crystal violet-iodine complex of gram stain - Gr- bacterium lose crystal violet-iodine complex Some bacteria naturally lack cell wall: Mycoplasma - bacterium causes mild pneumonia - have no cell wall, antimicrobial directed towards cell wall ineffective - sterols in membrane account for strength of membrane Bacteria in Domain Archaea - have a wide variety of cell wall types - none contain PTG but rather pseudoPTG |
Penicillin |
Binds proteins involved in cell wall synthesis. Prevents cross-linking of glycan chains by tetrapeptides. More effective against Gr+ bacterium: - due to increased concentration of PTG - Penicillin derivatives produced to protect against Gr- |
Lysozymes |
Produced in many body fluids including tears and saliva ie natural way. Breaks bonds linking NAG and NAM and destroys structural integrity of cell wall. Enzyme often used in lab to remove PTG layer from bacteria: - produces protoplast in G+ bacteria - produces spheroplast in G- bacteria |
Layers External to Cell Wall |
Capsules and Slime Layer General Function: - protection ~ protects bacteria from host defenses - attachment ~ enables bacteria to adhere to specific surfaces Distinct gelatinous layer Slime layer is irregular diffuse layer Chemical composition of capsules and slime layers varies depending on bacterial species, but most are made of polysaccharide. Referred to as glycocalyx (sugar shell). |
Flagella |
Long protein structure; Responsible for motility, use propeller like movements to push bacteria Can rotate more than 100,000 revolutions per minute (82 mph) ccw: forward movement, run cw: tumble Some are important in bacterial pathogenesis; Ex. H. pylori penetration through mucous coat; major cause of stomach ulcers/cancer ; |
Flagella Structure |
Three Basic Parts: Filament ~ extends to exterior, made of proteins called flagellin Hook ~ connects filament to cell; Basal Body ~ anchors flagellum into cell wall Flagella are rotary motors comprising a number of protein rings embedded in the cell wall. These molecular motors are powered by protein ;motive force.; Flagellin monomers self assemble into a left-handed helix - forming hollow tubular filament structure.; New monomers travel down tube and assemble at distal end of filament.; |
Chemotaxis |
Motile through sensing chemicals If chemical compound is nutrient, it acts as attractant. If compound is toxic, it acts as repellant.; Attractant or repellant bind to surface receptors in bacterial membrane. Binding of specific receptors initiates cascade of intracellular signaling that turns motor proteins.; |
Flagella Arrangement Schemes |
Monotrichous: one strand Lophotrichous: tuft on one end Amphitrichous: one strand on each end Peritrichous: everywhere |
Pili (fimbria) |
Considerably shorter and thinner than flagella Composed of protein subunits called pilin Function:; - attachment (fimbre) - movement - conjugation ~ mechanism of DNA transfer Hairlike appendage found on surface of many bacteria; Primarily composed of oligomeric pilin proteins |
Type IV Pili |
Adherence to sufaces:; External termini of the pili adhere to a solid substrate, either the surface to which the bacteria are attached or to other bacteria, and subsequent pilus contraction pulls the bacteria forward, like a grappling hook. Twitching motility: Movement is typically jerky, distinct from other forms of bacterial motility. ; |
Sex Pilus |
Pili connect the bacterium to another of its species, or to another bacterium of a different species, and build a bridge between the cytoplasms of either cell. That enables the transfer of plasmids between the bacteria. An exchanged plasmid can add new functions to a bacterium, like a antibiotic resisitance.; |