Bacterial Cell Structure Lecture 2&3 (Dr. Nasr) PDF

What is microbiology Study of Micro-organisms: Organisms that EXIST as Single Cells or cell clusters and must be viewed individually with the aid of a Microscope EXIST (Webster definition)To continue to be, have life; live HALLMARKS OF LIFE 1. METABOLISM (nutrient uptake, biomass, waste...

What is microbiology Study of Micro-organisms: Organisms that EXIST as Single Cells or cell clusters and must be viewed individually with the aid of a Microscope EXIST (Webster definition)To continue to be, have life; live HALLMARKS OF LIFE 1. METABOLISM (nutrient uptake, biomass, waste output) 2. DIFFERENTIATION (Bacillus spp. Caulobacter) 3. REPRODUCTION (binary fission) 4. COMMUNICATION (Pseudomonas aeruginosa) 5. EVOLUTION (antibiotic resistance, pathogens) Definition of the science of microbiology The science of Microbiology: microorganisms (microbes): microbial world (too small  1mm) Dates back only a few hundred years After discovery of microscope Three techniques had to be perfected before the science of microbiology could evolve beyond a primitive visionary state: 1. Microscopy 2. Sterilization 3. Pure culture methods  SIZE OF BACTERIA Unit for measurement : Micron or micrometer, μm : 1000 μm = mm Size: Varies with kinds of bacteria, and also related to their age and external environment.  Cocci: sphere, 1μm  Bacilli: rods , 0.5-1 μm in width, 3 μm in length  Spiral bacteria: 1~3 μm in length and 0.3-0.6 μm in width  Why study Microbiology ?? Microbiology as a BASIC Science Bacteria and yeast are useful in studying molecular biology, biochemistry and genetics --reproduce rapidly --are genetically (DNA) and biochemically more simple than higher order organisms --working with bacteria and yeast for understanding life processes has no ethical ramifications Microbiology as an APPLIED Science Medicine—Vaccine development, production of antibiotics, production of important biological enzymes and hormones (insulin) Industry—Production of fermented foods, cheeses and yogurt Agriculture—maintenance of soil fertility/digestion in cattle Ecology—Bioremediation microorganisms that degrade toxic waste materials  What organisms are considered to be studied in microbiology 1. BACTERIA 2. FUNGI 3. ALGAE 4. PROTOZOA 5. Viruses(although not a cellular entity but an intracellular pathogen) 6. Viroid (a DNA or RNA molecule cause plant diseases) 7. Prions (a biochemical anomaly—mis-folded proteins) 6 Kingdoms of Living Organisms  Prokaryotic & Eukaryotic Cells Bacteria Normal “flora” (Microbiota) Flora – microorganisms that are usually found associated with healthy body tissue What does that mean? Normal flora (microbiota) are bacteria which our body needs and play a ―good‖ role to help us stay healthy. Two kingdoms of Bacteria: Eubacteria – ―true‖ bacteria Archaebacteria – oldest organisms on earth, live in extreme conditions  Bacteria are: Unicellular Prokaryotic…which means? Fact: Each square centimeter of your skin averages about 100,000 bacteria. A single teaspoon of topsoil contains more than a billion (1,000,000,000) bacteria.  Bacteria Characteristics Some bacteria are aerobic, meaning that they require oxygen in order to survive. Other bacteria are anaerobes, meaning that they do not require oxygen to survive. Most bacteria are harmless and offer beneficial functions to living things and humanity. Bacterial cell structure: a singular, circular molecule of DNA tiny circular pieces of DNA called plasmids ribosomes  Bacteria have cell walls made of: Peptidoglycan (polysaccharide linked with chains of amino acids). this may be covered with an outer membrane of lipopolysaccharide (chain of sugar with a lipid attached).  Bacterial Cell Walls Peptidoglycan is material making up bacterial cell wall Thinner peptydoglycan layer Thicker peptydoglycan layer but no and outer membrane outer membrane  Cell wall :Common peptidoglycan layer A backbone of N-acetyl glucosamine and N-acetylmuramic acid: Both discovered in Gram positive and Gram negative bacteria. A set of identical tetrapeptide side chain attached to N-acetyl-muramic acid: different components and binding modes in Gram positive and Gram negative bacteria. A set of identical peptide cross bridges: only in Gram positive bacteria Some bacteria: have a gelatinous layer called a capsule surrounding the cell wall. form thick-walled endospores around chromosomes when they are exposed to harsh conditions (drought, high temperatures) Bacterial Capsule Capsules provide desiccation resistance, attachment to surfaces, and resistance to phagocytosis Capsules and slime layers  Attachment  Protection from phagocytic engulfment.  Resistance to drying.  Depot for waste products.  Reservoir for certain nutrients.  protection These are structures surrounding the outside of the cell envelope. They usually consist of polysaccharide; however, in certain bacilli they are composed of a polypeptide (polyglutamic acid). They are not essential to cell viability and some strains within a species will produce a capsule, whilst others do not. Capsules are often lost during in vitro culture. Endospores Some bacteria can form endospores, which are non- replicative cell forms that are highly resistant to environmental insult  Endospores  Identification (spores) of Bacteria  Pathogenesis  Resistance Dormant cell (rest phase) Resistant to adverse Produced when starved conditions Contain calcium dipicolinate - high temperatures DPA, Dipicolinic acid - organic solvents (chemicals) Bacillus and Clostridium - radiation Endospores Some bacteria have: flagella for motility (locomotion). pili (short, thicker outgrowths that help cell to attach to surfaces) Bacterial Flagella Flagella affect motility Movement can be down or up concentration gradients, e.g., toward food Some bacterial species are motile and possess locomotory organelles - flagella. Flagella consist of a number of proteins including flagellin Flagella The diameter of a flagellum is thin, 20 nm, and long with some having a length 10 times the diameter of cell. Due to their small diameter, flagella cannot be seen in the light microscope unless a special stain is applied. Bacteria can have one or more flagella arranged in clumps or spread all over the cell.  Identification of Bacteria  Pathogenesis  Motility of bacteria Monotrichate/Amphitrichate/Lophotrichate/Peritrichate  Distribution of Flagella Monotrichous  Lophotrichous Amphitrichous Peritrichous  Pili Pili are hair-like projections of the cell , They are known to be receptors for certain bacterial viruses. Chemical nature is pilin Classification and Function a. Common pili or fimbriae: fine , rigid numerous, related to bacterial adhesion b. Sex pili: longer and coarser, only 1-4, related to bacterial conjugation  Functions of Cell Wall Maintaining the cell's characteristic shape- the rigid wall compensates for the flexibility of the phospholipid membrane and keeps the cell from assuming a spherical shape Countering the effects of osmotic pressure Providing attachment sites for bacteriophages Providing a rigid platform for surface appendages- flagella, fimbriae, and pili all emanate from the wall and extend beyond it Play an essential role in cell division Be the sites of major antigenic determinants of the cell surface Resistance of Antibiotics Three bacterial shapes: 1. Rod shaped are called bacillus 2. Sphere shaped are called coccus 3. Spiral shaped are called spirillum Bacteria come in many different shapes and sizes…take a quick look… Gram positive = purple because of large amount of peptidoglycan in cell wall. Polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of bacteria. Gram negative = pink because¨ lipopolysaccharide membrane is removed by alcohol and thin peptidoglycan layer allows dye to escape. (LPS) is a large molecule consisting of a lipid and a polysaccharide (carbohydrate) joined by a covalent bond. Property Gram-positive cell wall Gram-negative cell wall Thickness of wall thick (20-80 nm) thin (10 nm) Number of layers many 1 or few Peptidoglycan (murein) >50% 10-20% content Teichoic acids in wall present absent Lipid and lipoprotein 0-3% 58% content Protein content 0 9% Lipopolysaccharide content 0 13% Sensitivity to Penicillin G yes no Sensitivity to lysozyme yes no  Cell membrane Site of biosynthesis of DNA, cell wall polymers and membrane lipids. Selective permeability and transport of solutes into cells. Electron transport and oxidative phosphorylation Excretion of hydrolytic exoenzymes  Cytoplasm Composed largely of water, together with proteins, nucleic acid, lipids and small amount of sugars and salts Ribosomes: numerous, 15-20nm in diameter with 70S; distributed throughout the cytoplasm; sensitive to streptomycin and erythromycin site of protein synthesis  Plasmids: extrachromosomal genetic elements  Inclusions: sources of stored energy, e,g volutin Nucleus Lacking nuclear membrane, absence of nucleoli, hence known as nucleic material or nucleoid, one to several per bacterium.  Plasmid Plasmids are small circular/line extrachromosomal, double-stranded DNA molecules. They are capable of self- replication and contain genes that confer some properties such as antibiotic resistance，virulence factors. Plasmids are not essential for cellular survival. Inclusions are aggregates of various compounds Inclusions of Granulose that are normally Bacteria involved in storing energy reserves or building blocks for the cell. Inclusions accumilate when a cell is grown in the presence of excess nutrients and they are often observed under laboratory conditions.  characteristics of typical bacterial cell structures Structure Function Chemical composition Flagella Swimming movement Protein Pili Stabilizes mating bacteria during DNA Sex pili Protein transfer by conjugation Attachment to surfaces; protection Common pili or fimbriae Protein against phagotrophic engulfment Attachment to surfaces; protection against phagocytic engulfment, Capsules Usually polysaccharide; occasionally occasionally killing or digestion; reserve (includes "slime layers" and glycocalyx) polypeptide of nutrients or protection against desiccation Prevents osmotic lysis of cell protoplast Peptidoglycan (murein) complexed with Cell wall in Gram-positive bacteria and confers rigidity and shape on cells teichoic acids Peptidoglycan prevents osmotic lysis and confers rigidity and shape; Peptidoglycan (murein) surrounded by Cell wall in Gram-negative bacteria outer membrane is permeability barrier; phospholipid protein-lipopolysaccharide associated LPS and proteins have various "outer membrane" functions Permeability barrier; transport of Plasma membrane solutes; energy generation; Phospholipid and protein location of numerous enzyme systems Ribosomes Sites of translation (protein synthesis) RNA and protein Often reserves of nutrients; additional Highly variable; carbohydrate, lipid, Inclusions specialized functions protein or inorganic Chromosome Genetic material of cell DNA Plasmid Extrachromosomal genetic material DNA Bacterial reproduction: Asexually (mitosis) using binary fission.  Sex pili effect the transfer of conjugative plasmids Conjugation Bacteria reproduce: sexually using conjugation Bacteria exchange plasmid DNA. This is how bacteria become antibiotic resistant.