Microbiology: Morphology of bacteria, cell structure, and more. PDF

Morphology of bacteria [Reading: pages 73-75] Coccus—spherical; Streptococcus pyogenes Bacillus—rod-shaped; Escherichia coli Spiral—three general types – Vibrio: curved or bent rods Vibrio cholerae (cholera) – Spirilla: rigid helical rods Spirilla volutan...

Morphology of bacteria [Reading: pages 73-75] Coccus—spherical; Streptococcus pyogenes Bacillus—rod-shaped; Escherichia coli Spiral—three general types – Vibrio: curved or bent rods Vibrio cholerae (cholera) – Spirilla: rigid helical rods Spirilla volutans (no disease) – Spirochetes: flexible helical rods Treponema pallidum (syphilis)  Monomorphic and Pleomorphic Monomorphic—cells have just one shape; the organisms listed above are monomorphic The majority of bacteria are monomorphic The cells of some bacteria have poorly defined shape, or have more than one shape; these are pleomorphic bacteria A pure culture of a pleomorphic bacterium will have cells with different shapes  Monomorphic and Pleomorphic (continued) Pleomorphic—cells of the bacteria can have several shapes; means variable in shape – Mycoplasmas: the cells do not have a cell wall; pliable; therefore take on various shapes – Corynebacterium diphthericum: rods, cocci, and club-shaped cells; causes diphtheria – Haemophilus influenzae: medically important pleomorphic bacteria; ear infections, meningitis  Three types of bacterial stains Simple stains: a single dye; stain MO for size, morphology, arrangement; examples methylene blue, nigrosin, crystal violet Differential stains: staining procedures that differentiate (distinguish) between groups of bacteria; require several steps; gram stain and acid-fast stain Structural stains: used to see cell structures like flagella, endospores, and capsules  Staining bacteria [Reading: page 59 and pages 64-66] Bacterial cells have a slight negative charge The chromophore, or colored ion, of most stains has a slight positive charge When cells are stained, the opposite charges attract and the cells absorb the stain Stained cells are much easier to see under the microscope than unstained ones  Staining bacteria (continued) A few special stains have negatively charged chromophores; are called negative stains When cells are stained with negative stains, the like charges repel and the cells do not absorb the stain; these cells remain clear, but the background is colored In a negative stain, the cells are colorless on a dark background; contrast is usually good  Staining bacteria (continued) Differential and structural stains require more than one stain; there is usually a decolorizer between the primary and secondary stains The purpose of the decolorizer is to wash the primary stain from certain cell structures or cells, but not from other cells or structures Decolorization is a critical step; too much can remove the primary stain when it should stay and too little can leave it in when it should go The prokaryotic cell Its anatomy in three parts: appendages, envelope, and protoplasm  axial filaments appendages flagella pili fimbriae Glycocalyx (capsule) Prokaryotic cell cell envelope cell wall plasma membrane* cytoplasm* ribosomes* protoplasm nucleoid region* granules inclusions plasmids *required for life; other structures may or may not be present in a given species  Appendages Flagella—long, whip-like structures; used for movement (motility); only some rod-shaped bacteria, vibrios, and spirilla have flagella Axial filaments—almost like a “fin” that runs length of cell; only on spirochetes; movement Pili—long cylinders made of protein; transfer DNA between cells & can help with motility Fimbriae—fibers for anchoring; many per cell  The bacterial envelope Glycocalyx—an outer “coat” that is usually made of carbohydrates; found outside the cell wall; capsules are one kind of glycocalyx Cell wall—a very important structure for both the bacterial cell and for microbiologists Plasma membrane—an important structure; regulates what enters and leaves the cell; very important in bacterial metabolism  Capsules Capsule—a viscous outer layer found just outside the cell wall; capsule is secreted by bacterial cell; usually made of carbohydrates Capsules help bacteria resist phagocytosis and so they can help bacteria cause disease The ability to form capsules is genetically determined, some cells cannot form them because they don’t have the genes for them  Cell wall [Reading: pages 81-85] The structure of the cell wall determines the gram reaction & acid-fast reaction of cells Medically important part of the bacterial cell – Many antibiotics work by damaging cell wall – Part of the gram-negative bacterial cell walls is poisonous; called endotoxin; endotoxins cause aches, fever, shock, and more and can be fatal – Cell walls are a defense for the bacteria; they can help bacteria resist host defenses  Good things (about cell walls) Human cells do not have cell walls at all Therefore, things that damage the cell wall usually do not harm human cells – lysozyme: enzyme in tears & saliva that degrades bacterial cell walls; effect on human cells? Ø – penicillin: chemical that prevents the synthesis of bacterial cell walls; effect on human cells? Ø Lysozyme & penicillin damage peptidoglycan which is in bacterial cells but not human cells  Bad things (about cell walls) Cell walls are a line of defense for bacteria – Help bacteria resist drying out (desiccation) Staphylococcus, Mycobacterium – Help them resist digestion inside phagocytes; Mycobacterium, Salmonella – The cell wall can be a barrier to antibiotics: gram-negatives are resistant to penicillin because the drug cannot cross the cell wall Cell walls can help bacteria resist attacks  Peptidoglycan [Reading: pages 80 and 81] Peptidoglycan (pg) is a chemical that forms an important part of bacterial cell walls Peptidoglycan is a hybrid molecule: – Hybrid can mean “made of two things” – Polysaccharide chains and small peptides The polysaccharide chains are very long and are cross-linked by the small peptides Peptidoglycan molecules are thin and flat; sometimes called “sheet-like”  Cell wall structure: gram + Have many, many layers of peptidoglycan, one on top of the other like coats of paint Running throughout the peptidoglycan layers are thread-like molecules called teichoic acids – Teichoic acid molecules strengthen cell wall – They aid in transport of materials through cell wall – Teichoic acids are g+ antigens: a part of the cell that causes animals to make antibodies  Cell wall structure: gram - Have one or a few layers of peptidoglycan Next, there is an outer membrane, which has a typical phospholipid bilayer structure – Outer membrane has a strong negative charge that repels phagocytes and defensive proteins – This outer membrane is a barrier to many drugs, disinfectants, and hydrolytic enzymes The outer membrane has many important biological molecules embedded in it  Cell wall structure: gram- (continued) Key things embedded in the outer membrane – Protein molecules called porins Porins are transport proteins (carriers) Provide passage for nutrients and other substances Are like the transport proteins of the plasma membrane – Lipopolysaccharide (LPS) molecules Hybrid molecules made of lipids and polysaccharides The polysaccharides are gram-negative antigens The lipid component is the endotoxin (poison)  Acid-fast cell walls Members of the genus Mycobacterium have acid-fast cell walls; M. tuberculosis (TB) Cell walls contain large amounts of a waxy lipid called mycolic acid; cell walls are tough Acid-fast bacteria are very resistant to desiccation, antiseptics, and disinfectants Acid-fast cell walls found only in two bacterial genera: Mycobacterium and Nocardia; most bacteria have gram (+) or gram (-) cell walls  Acid-fast cell walls (continued) While the mycobacteria are acid-fast, virtually all other bacteria are non acid-fast Mycobacterium tuberculosis causes TB; this bacteria is a problem because it is very resistant to desiccation & disinfectants; survives in dust/debris for a long, long time Furthermore, because of the tough cell wall, these bacteria are not digested by, and actually multiply inside, phagocytes  Acid fast stain Carbolfuchsin on smear; fuchsin is a bright red dye; carbol stands for carbolic acid, which softens the cell wall to let the dye in – All cells red Cells decolorized with acid alcohol – Acid-fast cells still red, all others clear Counter stain with methylene blue – Acid fast cells still red, all others blue  Plasma membrane Found between the cell wall & the cytoplasm Made primarily of phospholipid and protein Framework is the phospholipid bilayer Carrier proteins span the entire membrane and transport substances across membrane “Last part” of envelope when working inward  Protoplasm The “substance” of the cell; found inside the plasma membrane; pretty much “cytoplasm” Includes DNA, ribosomes, inclusions, proteins, carbohydrates, inorganic ions… Protoplasm is approximately 80% water Bacteria have no membranous organelles like nucleus, mitochondria, vacuoles, etc. Remember, all bacteria are prokaryotes and they don’t have internal membranes  Nucleoid region [Reading: page 90] aka nuclear area; or simply nucleoid Contains the bacterial chromosome – single, circular, DNA molecule – made of double-stranded DNA – has few million to several million nucleotides DNA contains the cell’s genetic blueprint; meaning the DNA contains cell’s genes Nearly all genes code for proteins previous | index | next E. coli cell that has “spilled” its chromosome. The DNA strands appear much wider than they really are.  Ribosomes [Reading: pages 90 and 91] Ribosomes are the sites of protein synthesis Protein synthesis is essential for life – A cell that cannot make proteins will die – The diphtheria toxin kills humans by stopping protein synthesis in the body’s cells Eukaryotic and prokaryotic ribosomes are different in structure and composition Bacterial ribosomes are 70S ribosomes Eukaryotic ribosomes are 80S ribosomes  Ribosomes (continued) The antibiotics erythromycin and tetracycline “kill” 70S ribosomes, but not 80S ribosomes Ribosomes are required for proteins; cells with “killed” ribosomes cannot make proteins and will be unable to reproduce (they die!!!) Streptomycin and chloramphenicol poison 70S ribosomes but not 80S ribosomes, too; these are rarely used because of side effects  Endospores [Reading: pages 92 and 93] “Resting” spores for bacterial survival With one exception, formed by gram + rods Form inside living cells; called sporogenesis After spore is formed the vegetative cell dies Endospore may remain dormant for years Under suitable conditions, endospore can germinate and form a new vegetative cell  Importance of endospores Resistant to heating, freezing, desiccation, antiseptics, and chemical disinfectants Difficult to control in clinical environments Some endospore-forming bacteria are serious pathogens – Clostridium: different species cause botulism, tetanus, food poisoning, and gas gangrene – Bacillus anthracis: most Bacillus species are harmless; B. anthracis is a deadly pathogen  Plasmids [Reading: pages 90, 234, and 243] DNA in cell that is not part of the chromosome Small, circular DNA molecules; usually 50-100 identical copies of a plasmid per cell Found in the cytoplasm of the cell Plasmids contain several different genes; each gene coding for new protein Plasmids are not required for survival under normal conditions; the “big” DNA is in nucleoid  Plasmids (continued) Plasmids are found only in gram-negatives Plasmids can be transferred between bacteria in process called conjugation – Donor cell (the one with plasmid) forms pili – Pili (pilus s.) dock with recipient cell – Donor cell copies plasmid and sends a copy through the pilus to recipient cell – Inside recipient cell, plasmid is copied until the normal 50-100 copies are present  Plasmids (continued) Plasmids are important to bacteria because they give bacteria new genes (characteristics) – Drug resistance: some plasmids have genes for enzymes that destroy antimicrobial drugs – Exotoxin production: some plasmids contain genes for protein toxins; toxins cause illness E. coli O157:H7 is deadly, unlike “ordinary” E. coli, because it received a plasmid from Shigella, a very serious pathogen; the plasmid contains the gene for the Shigella exotoxin “Photoshopped” True electron micrograph  Plasmids and medicine [Reading: page 244] Recall that plasmids can move between cells and transfer genes for drug-resistance and bacterial toxins; these are medical problems Plasmids can be put to good use, however As seen in the three slides below, scientists can isolate the gene for a medically important protein, put the gene into a plasmid, and then transfer the new plasmid to bacterial cells  Plasmids and medicine (continued) Growing bacteria with the plasmid containing the gene for the medically useful protein make the protein (in mass quantities) for us The medically useful protein can be extracted from the bacterial cultures & used by patients So, human insulin & human growth hormone can be made & purified to produce life-saving medicines for people in need  Plasmids and medicine (continued) The process from start to finish is technical and complex, but the idea is quite simple Once the gene for a protein has been isolated & transferred to bacterial cells, the process doesn’t need to be repeated; the cells are easily kept alive & will keep making protein While some plasmids pose medical problems, others are used to make valuable medicines Escherichia coli (greatly enlarged) DNA of Homo sapiens For insulin (Grown in pure culture) E. coli that produces human insulin Escherichia coli (greatly enlarged) DNA of Homo sapiens For human interferon (Grown in pure culture) E. coli that produces human interferon Escherichia coli (greatly enlarged) DNA of Homo sapiens For human growth hormone (Grown in pure culture) E. coli that produces human growth hormone  Viruses [Reading: pages 6 and 361-365] Very small things made of a nucleic acid genome encased in a protective shell Genome can be DNA or RNA, never both Viruses are acellular; they are not cells Viruses must infect host cells to make new virus particles; they cannot multiply on own A virus particle is called a virion  Virion size and shape With maybe one or two exceptions all virions are sub-microscopic (CLM) Their size varies between 25nm & 1000nm Good average size 50nm to 100nm Can easily be seen with electron microscopes Many virions are roughly “spherical” A good number are “rod-shaped” A few have unique shapes or are amorphous  Basic virus structure A virus particle is called a virion Components of the simplest virions (2) – Viral genome: the nucleic acid molecule(s) – Capsid: the protein coat that encases genome The capsid is made up of many, many individual protein molecules known as capsomeres The genome (DNA or RNA) and the capsid (coat) together form a nucleocapsid Virion showing capsid and genome  Advanced virus structure Many viruses have structures in addition to the nucleocapsid; the nucleocapsid is called the core when other structures are present Other structures found in some viruses – Envelope: surrounds the nucleocapsid; made of lipid & protein; comes from host cell membrane – Spikes: proteins on the surface of nucleocapsid or surface of the envelope; protrude from virion – Viral enzymes: usually found inside nucleocapsid Enveloped virion with spikes Transmission electron micrograph of the influenza virus. Note the numerous spikes along the outer edges of the virion.  Important notes The viral nucleic acid is called the genome Genome is found inside the capsid The genome together with the capsid is called the nucleocapsid All virions have a genome and a capsid; some virions have additional components, like the envelope, spikes, and/or enzymes The genome codes for viral proteins  Are viruses living or not Cannot synthesize proteins on their own Cannot replicate their nucleic acid on their own Cannot generate energy on their own Cannot multiply outside host cells They do, however “come alive” inside host cells No absolute “right answer” to this question Most biologists and virtually all virologists clearly consider viruses to be non-living Transmission electron micrograph of a rotavirus. Rotaviruses cause severe diarrhea, especially in children. A safe and reliable vaccine is available. This is a non-enveloped virus. The dark particles are empty capsids that formed without enclosing the viral nucleic acid (genome). TEM of variola virus (smallpox) Figure 13.1  Review of chemistry All matter made of atoms A pure substance w/ only “one kind” of atom is an element; carbon (C), oxygen (O or O2) A pure substance containing more than one kind of atom is a compound; C6H12O6 The breaking, forming and rearranging of chemical bonds is a chemical reaction benzene  Review of chemistry (continued) Molecules are structures formed when two or more atoms held together by chemical bonds Different atoms have different properties; the most important property for us is the number of chemical bonds that they form: – Carbon (C) = 4 – Hydrogen (H) = 1 – Oxygen (O) = 2 – Nitrogen (N) = 3  Two classes of substances [Reading: pages 34-36] Organic substances – Contain both carbon and hydrogen atoms – Sugars, proteins, fats; examples of biomolecules – Biomolecules are essential to life – Coal & oil are organic, but are not biomolecules Inorganic substances – Do not contain both carbon and hydrogen – Some are essential to life – Examples: water, minerals, oxygen  Composition of living things Bacterial cell (approximate) – Seventy per cent water – Twenty-nine per cent biomolecules – One per cent minerals Bony animal (approximate) – Seventy per cent water – Twenty-five per cent biomolecules – Five percent minerals  Water, biomolecules, and minerals Water “sets the stage” for life; the chemistry of life occurs in aqueous surroundings Biomolecules perform key functions and make structures that are essential to life Minerals and salts are important, too; they may: regulate water balance, help move substances across membranes, or be essential parts of some biomolecules  Carbon—the element of life Carbon atoms form four chemical bonds: – Carbon atoms can make intricate 3-D molecules – They can be chains, branched chains, rings Readily bonds with hydrogen, oxygen, nitrogen, and other carbon atoms Bonds are strong and stable Organic molecules have carbon “backbone” All biomolecules are carbon-based  Biomolecule summary Proteins—form the foundation of life by “putting together” all cell parts; control cellular function; form some cell structures Nucleic acids—contain plans for cell’s proteins; help cells make their proteins Carbohydrates—for energy; food storage; form some cell structures, like cell walls Lipids—food storage; for energy; form some cell structures, like membranes  Carbon—the element of life Carbon atoms form four chemical bonds: – Carbon atoms can make intricate 3-D molecules – They can be chains, branched chains, rings Readily bonds with hydrogen, oxygen, nitrogen, and other carbon atoms Bonds are strong and stable Organic molecules have carbon “backbone” All biomolecules are carbon-based  Proteins: general information [Reading: page 40] Most abundant class of biomolecule in cell – Minus H2O, a typical cell is ~50% protein Examples of proteins: – Exotoxins: bacterial toxins made of protein – Enzymes: cellular catalysts – Antibodies: defensive proteins in animals – Virus coat proteins: form virus shell or capsid Most diverse type of biomolecule in cell  Seven protein functions Transport—hemoglobin Enzymes—catalyze chemical reactions Defensive—antibodies help fight MO Storage—like in bean seeds Structural—keratin in skin and nails Signal—insulin Contractile—actin and myosin in muscle TED’S Ship Sank Completely Protein molecules make, or cause to be made through the actions of enzymes, all the structural and functional parts of the cell Nucleic acids (DNA and RNA) contain and help carry out the plans for making all of a cell’s proteins