BIO 3054 Microbial Cell Structure and Function Spring 2025 PDF

BIO 3054 Chapter 2 Microbial Cell Structure and Function Dr. Jyotisna Saxena University of Central Oklahoma Spring 2025 I. The Cell Envelope Series of layered structures surrounding cytoplasm and governs interactions with environment The...

BIO 3054 Chapter 2 Microbial Cell Structure and Function Dr. Jyotisna Saxena University of Central Oklahoma Spring 2025 I. The Cell Envelope Series of layered structures surrounding cytoplasm and governs interactions with environment The Cytoplasmic Membrane -Transporting Nutrients into the Cell The Cell Wall: rigidity and structure -Peptidoglycan, -The Outer Membrane (LPS) -Archaeal Cell Walls Diversity of Cell Envelope Structure Morphology of a Prokaryotic Cell Cells Lack Nucleus Plasma (Cytoplasmic) Membrane (1 of 6) Surrounds cytoplasm, and separates the cytoplasm from the environment Main function: selective permeability (nutrients transported in and waste products out) – Membrane proteins facilitate these reactions and also function in energy metabolism Bacterial and eukaryotic cytoplasmic membranes – General structure is phospholipid bilayer containing embedded proteins. Plasma (Cytoplasmic) Membrane (2 of 6) Phopsholipids: – Contain both hydrophobic (water-repelling) and hydrophilic (water- attracting) components ▪ hydrophilic (head) = glycerol + phosphate and other functional group ▪ hydrophobic (tails) = fatty acids – Fatty acids associate inward to form hydrophobic environment – hydrophilic “head groups” remain exposed to external environment or the cytoplasm. Phospholipid Bilayer Membrane  Plasma (Cytoplasmic) Membrane (3 of 6) Membrane proteins – peripheral membrane proteins: on the inner or outer surface of the plasma membrane, loosely attached – embedded proteins: integral/ transmembrane proteins - extend completely across membrane - some transmembrane proteins form channels  Plasma (Cytoplasmic) Membrane (4 of 6) “Fluid mosaic model" – Cytoplasmic membrane is as viscous as olive oil – Membrane is embedded with numerous proteins ▪ More than 200 different proteins are possible ▪ Proteins can function as receptors, transport gates, a mechanism to sense surroundings, etc. ▪ Proteins are not stationary – constantly changing position for various function – hence called fluid mosaic model Plasma (Cytoplasmic) Membrane (5 of 6) Cytoplasmic membrane is “selectively permeable” – Determines which molecules pass into or out of cell Few molecules pass through freely – Molecules pass through membrane via simple diffusion or transport mechanisms that may require carrier proteins and energy Transport proteins accumulate solutes against their concentration gradient protein anchor: Holds proteins in place. Energy conservation and consumption (METABOLISM) Generation of proton motive force (PMF) Cell membrane contains enzymes for ATP production  The Cytoplasmic Membrane (6 of 6) Archaeal cytoplasmic membranes – Ether linkages in phospholipids of Archaea – Ester linkages in phospholipids of Bacteria & Eukarya – Archaeal lipids have isoprenes instead of fatty acids. Nutrients transport across cell membrane (1 of 9) I. Passive transport: substances move from high concentration to low concentration; no energy expended – Simple diffusion, facilitated diffusion, and osmosis II. Active transport: substances move from low concentration to high concentration; energy expended Nutrients transport across cell membrane (2 of 9) Passive Transport: 1. Simple diffusion: movement of a molecule from its area of high concentration to an area of low concentration Movement continues until molecules are evenly distributed (have reached equilibrium) O2 and CO2 move through membranes via simple diffusion Nutrients transport across cell membrane (3 of 9) Passive Transport sva 2. Facilitated diffusion: integral membrane proteins serve as channels or carriers (transporters) membrane proteins facilitate the movement of ions or larger molecules across the membrane Substances move across a membrane with the concentration gradient (from arear of higher concentration to area of lower concentration) Transporter proteins – Some are very nonspecific – Others are more specialized Nutrients transport across cell membrane (4 of 9) Passive Transport Out In 3. Osmosis: the net movement of water across a selectively permeable membrane from an area of higher water concentration (lower solute concentration) to an area of lower water concentration (higher solute concentration) – Water flows to equalize solute concentrations inside and outside the cell – Inflow of water exerts osmotic pressure on membrane – Membrane rupture is prevented by rigid cell wall of bacteria Principle of Osmosis Isotonic solution: solute concentrations inside and outside of cell is same; water is at equilibrium – No net movement of water Hypotonic solution: solute concentration is lower outside than inside the cell; water moves into cell Hypertonic solution: solute concentration is higher outside of cell than inside; water moves out of cell Nutrients transport across cell membrane (5 of 5) II. Active transport – This is how cells accumulate solutes against concentration gradient i.e. from low to high conc. – energy expended (proton motive force (PMF), ATP, or another energy-rich compound) – Active processes can move a variety of ions as well as amino acids and sugars against the gradient Transporters (Figure 2.6) – three mechanisms ▪ Simple transport: transmembrane transport protein (PMF) ▪ ABC (ATP Binding Cassette) system: three components (binding protein, transmembrane transporter, ATP-hydrolyzing protein) ▪ Group translocation: series of proteins (energy rich compd.) Figure 2.6 The Three Classes of Transport Systems Energy-rich organic compound e.g. phosphoenol pyruvate (not proton motive force) drives transport. Best-studied system  Bacterial Cell Wall (1 of 7) Rigid structure Surrounds cytoplasmic membrane Determines shape of bacteria Prevents cell from bursting from osmotic/turgor pressure Unique chemical structure – Distinguishes Gram- positive from Gram-negative Gram stain reaction determined by cell wall thickness does not always correlate with envelope structure. Bacterial Cell Wall (2 of 7) Rigidity of cell wall is due to peptidoglycan (PTG) – Compound found only in bacteria – Not found in Archaea or Eukarya Basic structure of peptidoglycan – Alternating series of two subunits N-acetylglucosamine (NAG) N-acetylmuramic acid (NAM) – Stabilized by horizontal and vertical peptide cross- links often containing peptide interbridges Site of action of some antibiotics Penicillin interferes with the formation of the peptide cross-bridges that link the peptidoglycan rows, weakening the cell wall Bacterial Cell Wall (3 of 7) Gram-positive cell wall Relatively thick layer of peptidoglycan (PTG) As many as 30 Regardless of thickness, PTG is permeable to numerous substances Teichoic acid component of PTG ▪ Gram positive all cells commonly have teichoic acids (acidic molecules) embedded in cell wall and covalently linked to peptidoglycan ▪ Gives cell negative charge – lipoteichoic acids: teichoic acids covalently bound to membrane lipids  Bacterial Cell Wall (4 of 7) Gram-negative cell wall – Only contains thin layer of PTG – PTG sandwiched between outer membrane and cytoplasmic membrane Periplasm Porins: transmembrane protein channels for entrance and exit of solutes Bacterial Cell Wall (5 of 7) Gram-negative Outer Membrane Most of Gram-negative cell envelope composed of outer membrane Second lipid bilayer external to cell wall Periplasm Much like cytoplasmic membrane but outer leaflet made of lipopolysaccharides not phospholipids (polysaccharides covalently bound to lipids) hence known as lipopolysaccharide layer (LPS)  Bacterial Cell Wall (6 of 7) LPS: Lipopolysaccharide portion of Outer membrane – LPS serves as barrier to a large number of molecules Only small molecules or ions pass through channels – Portions of LPS medically significant O-polysaccharide: Used to identify certain species or strains – e.g. E. coli O157:H7 refers to O polysaccharide antigen Lipid A is an endotoxin, the toxic component of LPS Lipid A is toxic and can cause pain, fever, and damage to blood vessels The Gram-Negative Bacterial Cell Envelope Copyright © 2021, 2018, 2015 Pearson Education, Inc. All Rights Reserved The Cell Wall (7 of 7) Archaeal Cell Walls – Cytoplasmic membrane structure differs from Bacteria – Lack peptidoglycan – Typically lack outer membrane – Most lack polysaccharide wall, instead have S-layer (protein shell) – In methanogens, pseudomurein cell wall ▪ Similar to peptidoglycan ▪ Cannot be destroyed by lysozyme and penicillin Damage to the Cell Wall (1 of 2) Lysozyme: – Peptidoglycan can be destroyed by lysozyme (cleaves glycosidic bond between sugars) ▪ found in human secretions, major defense against bacterial infection https://www.youtube.com/watch?v=Jvo6IGKTvxA Penicillin blocks formation of peptide bridges in peptidoglycan  Damage to the Cell Wall (2 of 2) Gram-negative bacteria are not as susceptible to penicillin as Gram-positive bacteria – Outer membrane of Gram-negative cell wall blocks access of penicillin to its target Some other β-lactam antibiotics can penetrate the outer membrane and are effective at inhibiting growth of Gram-negative bacteria  Diversity of Cell Envelope Structure(1 of 2) S-Layers: para-crystalline structure consisting of protein or glycoprotein – If present, always outermost layer – Functions: strength, protection from lysis, conferring shape, creating periplasmic-like space, facilitating cell surface interactions, promoting adhesion, protecting cell from host defenses Alternative Configurations of the Cell Envelope – Outer S-layer surrounding Gram+ or Gram- bacterium – Many Archaea only have an S-layer outside cytoplasmic membrane – Pseuromurein cell walls in Archaea with or without S-layer – Archaea with outer membrane Diversity of Cell Envelope Structure (2 of 2) Some Bacteria and Archaea lack cell walls, – have tough cytoplasmic membranes (e.g., sterols) ▪ Mycoplasmas (Bacteria) ▪ Thermoplasma (Archaea)  Why is the external structure so important? Many antibiotics target the cell wall and other components of the cell envelope (cell membrane or outer membrane) An outer membrane complicates treatment with antibiotics, don’t forget about those toxins also It can allow for attachment to certain surfaces and also gives structure to the organism Morphology of a Prokaryotic Cell Cells Lack Nucleus Cell Surface Structures Capsules and Slime Layers (also known as Glycocalyx) – External to cell envelope – Many bacteria produce it, but not all – sticky polysaccharide coat – capsule: neatly organized, tightly attached, tight matrix; visible if treated with India ink – slime layer: unorganized, loosely attached, easily deformed Figure 2.16 Bacterial Capsules and Slime Formation Function of glycocalyx – Assists in attachment to surfaces – Prevents dehydration/desiccation – Contributes to virulence ▪ Capsules protects cells from phagocytosis (eating) by immune cells and help microbes adhere to body surfaces (attachment) – Bacillus anthracis – Streptococcus pneumoniae – Klebsiella pneumoniae – Extracellular polymeric substance helps form biofilms ▪ Protects cells, helps microbes attach to surfaces – Streptococcus mutans – Vibrio cholerae  Fimbriae and Pili Pili – Thin filamentous protein structure, ~2-10 nm wide – Enables organisms to stick to surfaces or form pellicles (thin sheets of cells on a liquid surface) or biofilms – Conjugation pili (or sex pili) involved in DNA transfer from one cell to another (conjugation) (Fig 2.18) – Electrically conductive pili conduct electrons – Produced by all Gram-negatives and many Gram-positives – Involved in motility (gliding and twitching motility+) ▪ Type IV pili adhere to host tissues and support twitching motility Fimbriae – Short pili mediating attachment to body surfaces (Fig 2.17) Neisseria gonorrhoeae E. coli O157 Pili Morphology of a Prokaryotic Cell Cells Lack Nucleus  Flagella, Archaella, and Swimming Motility (1 of 4) Flagella: structure that assists swimming in Bacteria (Archaella in Archaea) – long, thin appendages (15–20 nm wide) anchored in cell at one end (Figure 2.31) – tiny rotating machines that push or pull through liquid – Use propeller-like movements to push bacteria – Can rotate more than 100,000 revolutions/minute (82 mile/hour) – increase or decrease rotational speed relative to strength of proton motive force Flagella, Archaella, and Swimming Motility Flagellar arrangements: monotrichous, amphitrichous, lophotrichous, peritrichous – Some important in bacterial pathogenesis, e.g. H. pylori penetration through mucous coat Flagella proteins are H antigens and distinguish among serovars (e.g., Escherichia coli O157:H7) Chemotaxis (1 of 2) Taxis: directed movement in response to chemical or physical stimuli – chemotaxis: response to chemicals ▪ monitor/sample environment with chemoreceptors that sense attractants and repellents – phototaxis: response to light – Directed movement enhances access to resources or allows avoidance of damage/death – Bacteria and Archaea Osmotaxis: stimuli is ionic strength Hydrotaxis: stimuli is water Aerotaxis: stimuli is oxygen Chemotaxis (2 of 2) Measuring Chemotaxis – measured by inserting a capillary tube containing an attractant or a repellent in a suspension of motile bacteria ▪ Chemical concentration decreases with distance from tip ▪ Chemotactic bacteria swarm toward attractant, increasing number of cells in capillary ▪ can also be seen under a microscope Figure 2.40: Measuring Chemotaxis Using a Capillary Tube Assay Phototaxis of Phototrophic Bacteria Cell Inclusions (1 of 2) Inclusions function as energy reserves, carbon or phosphorus reservoirs, and/or have special fn. Enclosed by thin protein membrane Reduces osmotic stress Carbon storage polymers synthesized when carbon in excess ▪ broken down as carbon or energy sources if needed – glycogen: glucose polymer ▪ elemental sulfur accumulates in periplasmic granules (Figure b), oxidized to sulfate (SO42-) Cell Inclusions (2 of 2) Magnetosomes – allow bacteria to orient within magnetic field – biomineralized magnetic iron oxides – allow cell to undergo magnetotaxis: migration along magnetic field lines Buoyant Cyanobacteria Gas Vesicles – Confer buoyancy – Conical-shaped, gas- filled structures made of two proteins Endospores (1 of 2) produced inside certain bacterial cells when nutrients are depleted, unfavorable conditions (heat, dry) Specialized spores (Figure 2.25) resistant to desiccation, heat, radiation, chemicals Survival structures to endure unfavorable growth conditions A survival mechanism; not a reproductive process Vegetative → Endospore → Vegetative (Figure 2.26) Ideal for dispersal via wind, water, or animal gut Produced by members of Bacillus and Clostridium (Gram-positive) The Bacterial Endospore  Endospores (2 of 2) Endospore Formation or Sporulation – sporulation: vegetative cell differentiates to nongrowing, heat-resistant, light-refractive structure – Sporulation is triggered by limiting nutrient – can remain dormant for years but converts rapidly back to vegetative cell when conditions become favorable Germination – germination is triggered by nutrient availability – three steps: activation, germination, and outgrowth – special stains/procedures needed (e.g., malachite green) Formation of Endospores by Sporulation Endospore formation is complex and ordered Bacteria in vegetative state sense starvation and begin sporulation Vegetative cell will die while the spore remains Spore will go back to vegetative cell when favorable conditions return Endospore Germination in Bacillus  Differences Between Endospores and Vegetative Cells Characteristic Vegetative cell Endospore Microscopic appearance Nonrefractile Refractile Calcium content Low High Dipicolinic acid Absent Present Enzymatic activity High Low Respiration rate High Low or absent Macromolecular synthesis Present Absent Heat resistance Low High Radiation resistance Low High Resistance to chemicals Low High Lysozyme Sensitive Resistant Water content High, 80–90% Low, 10–25% in core Small acid-soluble spore proteins Absent Present Eukaryotic Cell Structure Why is it important to understand the differences between prokaryotic and eukaryotic cells? These differences are going to be very important when we discuss microbial control and your immune system The Eukaryotic Cell  Eukaryotic Organelles Membrane bound – Nucleus Ribosomes – Ribosomes – Endoplasmic reticulum – Golgi apparatus – Lysosome and vacuoles – Mitochondria and chloroplasts – Peroxisomes Other organelles: – microtubules, and microfilaments. – Flagella and cilia  Eukaryotic Plasma Membrane Similar in chemical structure and function of cytoplasmic membrane of prokaryote Phospholipid bilayer embedded with proteins Proteins in bilayer perform specific functions Transport Maintain cell integrity Receptors for cell signaling Membrane contains sterols for strength Animal cells contain cholesterol Fungal cells contain ergosterol Difference in sterols target for antifungal medications The Nucleus and Cell Division (1 of 4) Nucleus – Double membrane structure (nuclear envelope) that encloses the cell’s DNA ▪ Enclosed by two membranes that interact with nucleoplasm (inner membrane) and cytoplasm (outer membrane) – DNA is complexed with histone proteins to form chromatin / nucleosomes – During mitosis and meiosis, chromatin condenses into chromosomes Nuclear pore Nuclear envelope Nucleolus Chromatin The Nucleus and Cell Division (2 of 4) DNA molecules are wrapped around proteins to form fibers called chromatin / nucleosomes. ▪ Archaea also contain histones and nucleosomes; related to Eukarya Each very long chromatin fiber twists and folds to form a condensed chromosome. – Genes are short segments found on chromosomes that make you who you are. The Nucleus and Cell Division (3 of 4) The nucleus contains a darker area called a nucleolus The nucleolus is a particular location within the nucleus where ribosomes are made This area produces ribosomal RNA (rRNA), an important component of a ribosome. – Ribosomes are where proteins are made. DNA RNA Protein The Nucleus and DNA Packaging in Eukaryotes The Nucleus and Cell Division (4 of 4) Cell division – mitosis ▪ results in two diploid (two copies of each chromosome) daughter cells (somatic cells) – meiosis ▪ specialized form of nuclear division ▪ converts diploid into haploid cells ▪ results in four haploid (one copy of each chromosome) gametes Mitochondria and Chloroplasts (1 of 4) Mitochondria are the organelle for cellular respiration and oxidative phosphorylation for aerobic eukaryotes Uses oxygen to harvest energy (ATP) from sugar molecules number varies: few to 1000+ per cell surrounded by two membranes – cristae: folded internal membranes ▪ contain enzymes needed for respiration and ATP production – matrix: innermost area of mitochondrion ▪ contains citric acid enzymes ATP (Adenosine Tri-Phosphate) = Energy Currency of Cell Structure of the Mitochondrion Mitochondria and Chloroplasts (2 of 4) Chloroplasts – chlorophyll-containing organelle found in phototrophic eukaryotes – also present in Algae: Blue-green (cyanobacteria) – site of photosynthesis (the energy of sunlight in combination with water and carbon dioxide is used to create molecules of sugar – double membrane – inner membrane surrounds stroma, which contains large amounts of RuBisCO (key enzyme for Calvin cycle that converts CO2 to organics) – thylakoids: flattened membrane discs contain chlorophyll and ATP synthetic components, form proton motive force The chloroplast - photosynthesis © 2017 Pearson Education, Inc. Chloroplasts of a Diatom and a Green Alga Cell Mitochondria and Chloroplasts (3 of 4) Specialize in energy metabolism Evolutionary roots within Bacteria Endosymbiotic origin of the two organelles: Endosymbiosis is when one species lives inside another host species (think of “Pac Man”) Mitochondria and chloroplasts, appear to have evolved from small, free-living respiratory and phototrophic prokaryotes, respectively, that were engulfed by another prokaryotic cell Evidence: Mitochondria and chloroplasts contain circular DNA genomes and ribosomes (70S) similar to those of Bacteria. The mitochondria and chloroplast likely originated from endosymbiosis. Endosymbiosis is when one species lives inside another host species. Mitochondria and Chloroplasts (4 of 4) – Eukarya hypothesized to have originated from symbiotic fusion of archaeal host and mitochondrial endosymbiont. – Later, eukaryotic host cell acquired a chloroplast endosymbiont to become ancestor of phototrophic eukaryotes Root = LUCA (Last Universal Common Ancestor) Endoplasmic reticulum (ER) Network of membranes continuous with nuclear membrane ▪ Two types (rough and smooth) – Rough ER: contains attached ribosomes; smooth does not. – Smooth ER: participates in the synthesis of lipids (fats, steroids, hormones) and carbohydrate metabolism. – Rough ER produces glycoproteins and new membrane material. Golgi Apparatus Transport organelle Modifies proteins produced by rough ER Finishes, sorts, and ships cell products (FedEx of Cell) Transports modified proteins via secretory vesicles to the plasma membrane and other regions Produces glycoproteins, lipoproteins, glycolipids Produces lysosomes Lysosomes: membrane-enclosed compartments containing digestive enzymes and recycling cell components Present in phagocytic cells (immune cells) Flagella and Cilia – Present on many eukaryotic microbe surfaces. – Function in motility, allowing cells to move by swimming. – Cilia are short flagella that beat in synchrony. – Eukaryotic flagella are long appendages that propel through whiplike motion. – Structurally and functionally differ from prokaryotic flagella Copyright © 2021, 2018, 2015 Pearson Education, Inc. All Rights Reserved Other Eukaryotic Cell Structures (1 of 3) Cytoskeleton: internal structural support The cytoskeleton is a network of protein fibers that provides mechanical support, anchorage, and reinforcement. The cytoskeleton network can be quickly dismantled and reassembled, providing flexibility. – microtubules ▪ hollow tubes 25 nm in diameter; composed of α- and β-tubulin ▪ maintain cell shape, facilitate motility; move chromosomes and organelles – microfilaments ▪ 7 nm in diameter; polymers of actin protein ▪ maintain and change cell shape; involved in amoeboid motility and cell division – intermediate filaments ▪ 8–12 nm in diameter; fibrous keratin proteins ▪ maintain cell shape and position organelles Tubulin and Microfilaments  Class activity In groups- research one cell structure (endospore, flagella, pili (type IV), capsule, inclusions, gas vesicle, slime layer)- find function and example of a microbe that uses it and how, is it in Gram positive/ negative/ Archaea?