Prokaryotic Structure 2024 PDF

Prokaryotic Structure  Why is knowing structure important? To better facilitate our understanding of – Pathogenesis – Disinfection – Chemotherapy (antibiotics) – Immune recognition and response – Cultivation, growth and identification  The Prokaryotic Cell Stru...

Prokaryotic Structure  Why is knowing structure important? To better facilitate our understanding of – Pathogenesis – Disinfection – Chemotherapy (antibiotics) – Immune recognition and response – Cultivation, growth and identification  The Prokaryotic Cell Structural Features – Cell Membrane – Cell Wall Genetic Features – Nucleic Acid – Ribosome Special Structures – Attachment/Motility – Endospore – Capsule Cell membrane (all cells) Phospholipid bilayer – fatty acid tails (interior), phosphate bound-glycerol (exterior) Outside Inside Permeability barrier to large macromolecules – but not to gases, water, small compounds (Semi-permeable) Water, Lipid-soluble molecules, gases (02, CO2) Cell membrane Transport Passive Diffusion Embedded proteins – Movement of molecules specialized transport down a gradient into/out-of cells Facilitated diffusion – Diffusion directly through Active transport membrane nutrient regulation and some – No energy expended metabolic synthesis Site of energy generation (ATP) in bacteria Cell membrane Generation of energy by Proton Motive Force PMF is a chemiosmotic gradient which fuels ATP production and metabolism Cell membrane Process of Osmosis (water regulation) Hypertonic Salt outside Ouch! Water moves out of cell Hypotonic Salt outside Water moves into cell Isotonic Inside = Outside Hypotonic example – dropping a bacterium into distilled water No net water movement Water molecules also move down a concentration gradient  Bacteria are protected by a rigid cell wall Peptidoglycan *(chief structural component) – Rigid – Helps resists osmotic stress – Provides shape – Found in most, but not all bacterial species – Target for some antibiotics – Similar structure is found in Archaea * pep-təd-ō-glī-kan Peptidoglycan (chemical composition) The Bricks Alternating sugar subunits (bricks) form glycan chains – N-acetylglucosamine (NAG)* – N-acetylmuramic acid (NAM)* The Mortar Chains are tied together through interchain peptide crosslinks – Tetrapeptide linkage with or without peptide interbridge – Peptide interbridge is only in “Gram- Positive” type bacteria Peptidoglycan as a target Antibiotics which target crosslinking – Penicillins – Cephalosporins Compounds that break glycan chanins – Lysozyme Loss of peptidoglycan results in L (Lister) forms – Results in lysis Differences in Peptidoglycan Structure Revealed by the Gram stain (Hans Christian Gram) Differential staining process which yields one of two outcomes: Peptidoglycan Gram positive configuration 20-80 nm thick – This thickness results in the retention of Crystal Violet & Iodine Contains embedded teichoic / lipoteichoic acids – Provide additional rigidity and perhaps growth regulating properties Peptidoglycan Gram negative configuration Thinner peptidoglycan layer Protected with an outer membrane containing lipo-poly-saccharide* Periplasmic space lays between the lipid membranes and contains the peptidoglycan Lipopolysaccharide (LPS) Outermembrane component of all Gram negative bacteria Heat stable / Can be released Lipid A portion is toxic – Endotoxin Core polysaccharide Oligosaccharide – Can be strain specific and immunologically recognized E. coli O157:H7 Lipopolysaccharide Septic Shock LPS Cellular Receptors Inflammatory Cytokines Vasodilation Vascular Leakiness Clotting Cascade Bacterial morphology Shapes and arrangement of bacteria  Additional layers Used for Stability Attachment Drug resistance S layers Protein Capsules/Glycocalyx Carbohydrate Bacterial polysaccharide sheaths Capsules, slime layers and films Negative Stain Usually composed of polysaccharide Usually correlated with virulence (pathogenicity) Promotes attachment Reduces phagocytosis Facilitates communication and formation of colonies  Bacteria with atypical cell walls Acid-fast bacteria Presence of mycolic acid (waxy lipid) Present unique challenges to detection and treatment Found in – Mycobacteria* species – Norcardia species  Bacteria with atypical cell walls No peptidoglycan or cell wall Mycoplasma* species – Lack cell walls – Membrane has sterols (i.e. cholesterol) – Small and pleiomorphic organisms – Include several species which are human pathogens End of first half  Prokaryotic structure Interior and specialized features Bacterial genome (DNA) No nucleus: DNA is stored in the nucleoid Posses a (usually) single circular chromosome Presence of plasmids – Carry extra genes for metabolism or pathogenicity – Present in many, but not all species – May be used to pass genetic Bacterial genome = 3-5 million information between species base pairs (but whose counting ?) Bacterial ribosomes (protein synthesis) Just the facts: Assemblages of protein and RNA Responsible for protein synthesis Can exist free in cytoplasm Many may be associated with mRNA and form Did you know? About 50% of antibiotics polysomes target the bacterial ribosome? Structures present in some, but not all species of prokaryotes Bacterial Storage Glycogen Inclusions Polyhydroxybuterate Storage vacuoles of Sulfur crystals various materials Polyphosphate crystals – Energy substrates Iron oxide – Metabolic precursors (magnetosomes) – Orientation May be characteristic or diagnostic of a particular species Bacterial Attachment Pili/Fimbriae Structures which facilitate attachment – Important in colonization and pathogenicity Structures which facilitate conjugation – Sex pilus – Important in the transfer of genetic information Bacterial endospores Endospore formers A medical problem – Bacillus – Clostridium Endospores are ubiquitous – Sporosarcina – Clostridioides (found everywhere in the – Sporolactobacillus environment – soil) Extremely resistant to most disinfection methods (except for autoclaving or methods of sterilization) Disease examples Endospores can germinate – Anthrax (Bacillus) – Botulism (Clostridium) in stored food, or the – Gas gangrene (Clostridium) human body – Tetnus (Clostridium) Bacterial endospores A long term survival trait  6 to 8 hours  Bacillus subtilis – Source: Libretexts, Biology Bacterial movement Flagella structure and arrangement Composed of flagellin monomers Present in some, not all, bacteria Movement is via flagellar rotation Energy is provided by the PMF Bacterial movement Photosynthetic Bacteria Photosynthetic bacteria Cyanobacteria Green and purple sulfur (blue/green) bacteria Gram neg. structure Use bacteriochlorophyll Uses chlorophyll a in Live in anaerobic structures similar to environments (do not plants (thylakoids) give off O2) Found largely in (but Use sulfur (H2S) in their not limited to) aquatic energy metabolism environments Produce O2  Archaea So unique they have their own domain! Archaea Most primitive of life forms Adapted to the nastiest, extreme environments Possess both prokaryotic and eukaryotic features – No peptidoglycan in their cell wall – “Eukaryote-like” ribosomes  Summary Prokaryotes are classified based on their lack of a true nucleus and include the domains of Archaea and Bacteria Bacteria can be classified on a variety of features, especially on the nature of their cell wall (Gram +, Gram - , Acid fast) Bacteria can posses unique structures like pilli, flagella, inclusion, capsules, and endospores. Different structures allow individual species to adapt to their niche or exhibit pathogenicity