L2 Prokaryotic Cell Structure PDF

L2: Prokaryotic cell structure BIO-440 Jan 17, 2025 By Dr. Anny Cárdenas Assistant Professor, Department of Biology 1 Content Topic 1: Introduction- Microscopy and cell structure Topic 2: Cell envelope: Cytoplasmic membrane, Cell wall, Ou...

L2: Prokaryotic cell structure BIO-440 Jan 17, 2025 By Dr. Anny Cárdenas Assistant Professor, Department of Biology 1 Content Topic 1: Introduction- Microscopy and cell structure Topic 2: Cell envelope: Cytoplasmic membrane, Cell wall, Outer membrane, S-layers Topic 3: Cell surface and inclusions Topic 4: Cell locomotion and chemotaxis Early microscopy Van Leeuwenhoek’s drawings of A replica of Antoni van bacteria (1684) A drawing of the microscope Leeuwenhoek’s microscope. used by Robert Hooke in 1664. Brock 16th edition, ©Pearson Light microscopy pigmaged usuallyneedto stain Uses visible light and lenses to Bright-field photomicrographs of pigmented sams magnify the sample. microorganisms 2 Specimens are visualized because of differences in contrast that exist between them and their surroundings bright-field phase-contrast differential interference contrast dark-field fluorescence. Brock 16th edition, ©Pearson  Brock 16th edition, ©Pearson Light microscopy: staining Gram staining Fluorescence staining Uses visible light and lenses to magnify the sample. Specimens are visualized because of differences in contrast that exist between them and their surroundings bright-field phase-contrast differential interference contrast dark-field fluorescence.  Brock 16th edition, ©Pearson Electron microscopy Uses electrons (much shorter wavelengths) instead of light toteyinteter Much higher magnification and resolutione View structures at the molecular level Transmission Electron Scanning Electron Microscopy Microscopy (TEM) (SEM) elections of seam Sends electrons through a very Scans the surface of a sample with thin sample to look at the internal electrons to create a 3D image of structure. the outer structure. Cell envelope: series of layered structures that surround the cytoplasm and govern cellular interactions with the external environment. 1 Cytoplasmic membrane 2 Cell wall 3 Outer membrane 4 S-layers 1 Cytoplasmic membrane: surrounds the cytoplasm Bacteria and Eukarya! 1 Cytoplasmic membrane: surrounds the cytoplasm Integral onmembrane fitia proteins Peripheral membrane proteins  1 Cytoplasmic membrane: Archaea vs Bacteria and Eukarya Archaea Bacteria and Eukarya i 1. Phosphoglycerol diether lipids 3. Ether linkage Ester linkage 4. Monolayers Fatty acid chains it i 2. Isoprenoid chains pressureetempenviro eftremupniieiig 1 Cytoplasmic environments membrane: Archaea can live in extreme 1 Major functions of the cytoplasmatic membrane 2 The cell wall: A layer outside the cytoplasmic membrane that protects against osmotic lysis and maintain cell shape and rigidity L Gram positives Gram negatives tianya.ci membranes this Emma said.it Mycobacteria don’t have a cell wall! 2 The cell wall: Bacterial cell walls - peptidoglycan The sugar backbone of peptidoglycan is composed of alternating repeats of two modified glucose residues called N-acetylglucosamine and N-acetylmuramic acid joined by a B(1-4) linkage variation Attached to the N-acetylmuramic acid residue is a short peptide side chain. The amino acid composition of this peptide side chain can vary considerably between bacterial species. 2 The cell wall: Bacterial cell walls - peptidoglycan 2 The cell wall: Archaeal cell walls Archaea lack peptidoglycan and typically lack an outer membrane Pseudomurein  gramnegative 3 The outer membrane: is a second lipid bilayer found external to the cell wall, but its structure and function differs from that of the cytoplasmic membrane. use 2199mg LPS Surface recognition Virulence factor Mechanical strength 3 Lipopolysaccharide (LPS): often referred to as endotoxin in the context of its toxic effects. Ketodeoxyoctonate (KDO) know parts Heptose (Hep) Glucose (Glu) Triggers a Galactose (Gal) strong immune N-acetylglucosamine (GluNac) reaction in Glucosamine (GlcN) animals Highly variable among species! Phosphate (P) conservednot specific endotoxin 3 Porines: Unique to the outer membrane and function as channels for the entrance and exit of solutes substrates Porins 91 In The outer membrane is far more permeable than is the cytoplasmic membrane! 3 Periplasm: space located between the outer surface of the cytoplasmic membrane and the inner surface of the outer membrane Periplasm Hydrolytic enzymes (initial degradation) Binding proteins (transport) Chemoreceptors 4 S-layers: found in many bacteria and nearly all archaea When present, it is always the outermost layer of the cell envelope Can take on the role of the cell wall -> structural strength, protecting the cell from osmotic lysis, and conferring cell shape. Can also create a periplasmic-like space in Archaea Different configurations of the cell envelope gramnegativewSlayer Archaea Mycobacteria Gramnegative Cell surface and inclusions 1 Capsules and Slime Layers 2 Fimbriae and pili 3 Carbon Storage Polymers 4 Polyphosphate, Sulfur, and Carbonate Minerals 5 Gas Vesicles 1 Capsules and slimes: used to describe a sticky coat of polysaccharide formed outside of the cell envelope. Involved in attachment and protection Leuconostoc Capsules of Acinetobacter TEM micrograph of Rhizobium mesenteroides contains species observed by phase- leguminosarum stained with ruthenium red a thick dextran (glucose contrast microscopy after to reveal the capsule polymer) slime layer negative staining with India ink formed by the cells. 2 Fimbria and pili: filamentous structures made of protein that extend from the surface of a cell and can have many functions (attachment, motility, cell recognition, genetic exchange) have Eats Fimbria Pili (singular, pilus) theyattachcellstosurface 3 Carbon storage polymers One of the most common inclusion bodies in prokaryotic organisms is poly-β-hydroxyalkanoates (PHAs) aggregated into granules. Another carbon storage inclusion is glycogen limitationin dueto sources carbon 4 Polyphosphate, sulfur, and carbonate minerals Many prokaryotic and eukaryotic microbes accumulate inorganic phosphate in the form of polyphosphate granules when phosphate is in excess and can be drawn upon as a source of phosphate for nucleic acid and phospholipid biosynthesis when phosphate is limiting. Sulfur bacteria can accumulate elemental sulfur (S0) in the cell in microscopically visible granules. as the sulfur source becomes limiting. Heliobacterium modesticaldum Isochromatium buderi When sulfur in the granules is oxidized to sulfate (SO42-) the granules slowly disappear 4 Polyphosphate, sulfur, and carbonate minerals The cyanobacterium Gloeomargarita containing granules of the mineral benstonite 5 Gas vesicles Some Bacteria and Archaea can float because they contain gas vesicles, structures that confer buoyancy and allow the cells to position themselves in regions of the water column that best suit their metabolisms. want they tobe asexposed astheycantosun Flotation of a bloom of gas-vesiculate cyanobacteria in a freshwater lake. Cell locomotion Bacterial flagella (singular, flagellum) and archaeal archaella (singular, archaellum) Flagella and archaella are tiny rotating machines that function to push or pull the cell through a liquid. Polar flagella: flagella are attached to one or both ends of the cell done swimmingis byflagella Peritrichous flagella: groups or flagella (tufts) are inserted around the cell Flagella can rotate at up to 1000 revolutions per second to support a swimming speed of up to 60 cell-lengths/sec (A cheetah, can move at about 25 body-lengths/sec) Movement in peritrichously and polarly flagellated prokaryotic cells CCW -> forward motion Reversible flagella: CCW -> forward motion, CW -> cell reverses CW -> cell tumbles unidirectional flagella: CCW -> forward motion Structure and function of flagella Flagellar motor is composed of > 25 proteins anchored in the cytoplasmic membrane and cell wall Filament: main part of the flagellum, composed of many copies of flagellin Hook: single protein that connects the base with the filament L ring: Anchored in the OM P ring: Anchored in the Peptidoglycan layer MS ring: Anchored in the cytoplasmic membrane C ring: Anchored in the cytoplasm Export apparatus: Mediates the flagellar synthesis Flagellar rotation occurs at the expense of energy Proton motive force: proton translocation through channels within the stator complex cause the MS ring to rotate, thereby driving rotation of the attached rod and flagellum. Surface motility Surface motility requires the attachment to a surface and is independent of flagella or archaella. Surface motility: Gliding is defined as a smooth motion along the long axis of a cell without the aid of external propulsive structures (such as pili or attachment organelles) Requires adhesion proteins! AdhesiveProteins mediate of rotation cells Surface motility: Gliding is defined as a smooth motion along the long axis of a cell without the aid of external propulsive structures (such as pili or attachment organelles) Gliding bacteria are typically Nongliding mutant filamentous or rod-shaped in Flavobacterium johnsoniae gliding away from the strain of F. morphology center of the colony johnsoniae Surface motility: Twitching is a form of surface motility caused by the extension and retraction of type IV pili. Pseudomonas aeruginosa twitching motility Chemotaxis is the directed movement of an organisms toward (positive) or away from (negative) a chemical gradient. Chemotaxis can be measured in a chemotaxis assay in which a small glass capillary tube containing an attractant is immersed into a suspension of motile bacteria. Other taxis: Phototaxis attractiontolight Alexandre, G. (2015): 3230-3237. Journal of bacteriology, 197(20), 3230-3237 Other taxis: Magnetotaxis Amor, M, et al (2020) Environmental Microbiology 22, no. 9: 3611-3632. Questions? 43