Procaryotic Profiles
Appendages: Cell Extensions
Reference: https://sites.google.com/site/rccmicrobiology/chapter-4-procaryotic-profiles
- Appendages: structures that are outside the surface of bacteria.
- Flagella (Bacteria Propellers)
- Flagellum: appendage that offers mobility, self-propulsion, to swim freely in an aqueous habitat.
- Bacteria flagellum consists of 3 parts:
- 1. Filament
- Helical structure composed of proteins.
- Size: 20nm in diameter, 1-70nm in length.
- 2. Hook (Sheath)
- Filament inserted through curved, tubular hook.
- The hook is anchored by the basal body.
- 3. Basal Body
- Stack of protein rings that anchors the flagella through the cell wall to the cell membrane.
- Structure allows for 360 degree to propel in a direct foward movement.
- Types of Arrangement
- Monotrichous: single flagellum.
- Lophotrichous: small bunches of flagella emerging from the same site.
- Amphitrichous: flagella coming from both poles of the cell.
- Peritricous: flagella is dispersed randomly over the surface of the cell.
- Functions
- Chemotaxis: detect and move in response to chemical signals.
- Run: smooth linear direction toward a stimulus.
- Tumble: reversal of direction and stops to change course.
- Phototaxis: type of movement in response to light rather than chemicals.
- Periplasmic Flagella: Internal Flagella
- Spirochetes: corkscrew-shaped bacteria.
- Spirochetes have a mode of transportation caused by two or more long, coiled threads called the periplasmic flagella or axial filaments.
- Periplasmic flagella:
- Pilus & Fimbria
- Appendages that provide some form of adhesion, but not locomotion.
- Fimbria are refereed to as shorter, numerous strands.
- Stick to each other and surfaces.
- Can lead to biofilms and other aggregates on the surface of liquid.
- Or colonization on inanimate objects.
- Also can colonize and infect host because of tight adhesion between with fimbriae and and epithelial cells.
- Pili are refereed to as longer, sparser appendages.
- Elongated, rigid tubular structure made of pilin.
- Found only in Gram negative bacteria.
- Conjugation: partial transfer of DNA from one cell to another.
- Takes place only with compatible gram negative cells.
- Cell envelope: complex external covering that lies outside of the cytoplasm in most bacteria.
- Acts as a single protective unit.
- Three Basic Layers of Cell Envelope
- Glycocalyx
- Coating of macromolecules to protect the cell.
- Slime layer: loose, soluble shield that protect cells from loss of water and nutrients.
- Capsules: repeating polysaccharide units, of protein, or both.
- Capsule is more tightly bound to cell than a slime layer.
- Prominently sticky (mucoid) is a characteristic of most encapsulated bacteria.
- Specialized Functions of Glycocalyx
- Protection from phagocytes.
- Cell Wall
- Structure
- Cell wall important for determination of shape.
- Provides strong structural support from bursting or collapsing due to osmotic pressure.
- Most bacteria get rigidity of cell wall from a macromolecule called peptidoglycan (PG).
- Composed of repeating framework of long glycan chains cross-linked by short peptide fragments (like wire-mesh).
- Peptidoglycan structure is composed of carbohydrate backbone and amino acids.
- Carbohydrate backbone (disacharides) is made of NAM (N-acetylmuramic acid) and NAG (N-acetylglucosamine).
- Crossed with polypeptides, amino acids (peptide cross-bridge amino acids & side chain amino acid).
- Amount and composition vary.
- Bacteria often live in aqueous habitats with low a low solute concentration and are susceptable to osmosis.
- Osmosis
- Movement of water across a selectively permeable membrane from a higher water concentration to a lower water concentration.
- Osmotic pressure: pressure needed to stop the movement of water across the membrane.
- Isotonic solution: no net movement
- Hypotonic solution: water moves into the cell and may cause the cell to burst if the wall is weak or damaged (osmotic lysis).
- Less solutes outside the cell.
- hypOtonic = cell gets bigger.
- Osmotic lysis.
- Hypertonic solution: water moves out of the cell, causing its cytoplasm to shrink (plasmolysis).
- Some drugs target the peptide cross-links in the peptidoglycan and causes the cell to lyse.
- Some disinfectants damage the cell walls.
- Lysozyme, enzyme in tears and saliva, can hydrolyze the bonds in the glycan chains and cause the wall to break down.
- Differences in Cell Wall
- Gram stain: staining technique to reveal two distinguishable cells.
- Primary stain: crystal violet.
- Absorbed by peptidoglycan and reinforced by gram's iodine.
- Alcohol: removes the color, but in Gram+ the dye is stuck in the membrane.
- Secondary stain: safranin.
- Stains the colorless cell.
- Gram+ Cells
- Cell wall can range from 20-80nm.
- Composed of Teichoic Acid and Lipoteichoic Acid and Peptidoglycan
- Periplasmic space: small.
- Metabolic enzymes.
- Disinfecting this cell is going to kill it easier due to peptidoglycan layer easier to dissolve.
- Permeability: more penetrable.
- Some cell walls are harmful to humans.
- Gram- Cells
- Cell wall can range from 8-11nm.
- Composed of Lipopolysaccharide and Lipoprotein and Peptidoglycan.
- Periplasmic space: large.
- Metabolic enzymes.
- Permeability: less penetrable.
- Outer membrane contains: Lipid A, O Polysacharide, & porin proteins.
- Porin proteins allow transfer of molecules and can change size.
- Provides extra protection from antimicrobial chemicals.
- Cause fever and shock reactions due to lipids on outer membrane (endotoxins).
- Non-typical Cell Walls
- Acid-fast stain: A gram+ wall with 60% Lipids.
- Acid-fast keeps it's colors regardless of staining.
- TB, Leprosy.
- Archeae: some lack cell wall, but they carrie a pseudopeptidoglycan.
- Mutations can result in L forms.
- L forms (L-mutants): mutation of a wall less cell.
- Wall can be removed with lysozyme or penicillin which disrupts peptidoglycan bonds.
- Gram negative cell without wall: spheroplast.
- Gram positive cell without wall: protoplast.
- Fragile cell that can easily lyse.
- Cell Membrane
- Very thin, 5-10nm.
- Cell membranes are mostly composed of mostly phospholipids and proteins.
- Mycoplasmas are an exception which contains high amount of sterols, as well as archeae which have hydrocarbons.
- Mesosomes: internal pouches that increase internal surface area, participate in cell wall synthesis, and guide duplicated bacterial chromosomes into daughter cells.
- Functions for Bacteria
- Energy reactions.
- Nutrient processing.
- Synthesis
- ATP synthesis and enzymes of respiration reside in cell membrane due to no mitochondria.
- Macromolecules are also constructed for the cell envelope and appendages.
- Transport
- Passage of nutrients into the cell and discharges waste.
- Selectively permeable membrane.
- Glycocalyx and cell wall block the passage of large molecules.
- Membrane secretes metabolic products into the extracellular environment.
- Cell pool: complex mixture of nutrients including sugars, amino acids, and salts.
- Also contains chromatin body, ribosomes, mesosomes, and granules.
- Bacterial Chromosomes and Plasmids
- Bacterial chromosome: single circular strand of DNA.
- Aggregated in a dense area called the nucleoid.
- Plasmids: tiny, extra-chromosomal strands.
- They are duplicated and passed on.
- Not essential, but they often carry protective traits (drug resistance, enzyme and toxin production).
- Ribosomes: tiny, discrete units that are responsible for protein synthesis.
- Composed of rRNA and protein.
- S unit, Svedberg unit is used to characterize ribosomes.
- Heavier more compact structures fall down faster.
- Procaryotic cell has a 70S (composed of two units: 50S and 30S).
- Inclusions, of Grunules: Storage Bodies
- Inclusion bodies (inclusions): stores nutrients during times of abundance to be used when nutrients are scarce.
- Can store energy rich substances, glycogen, and poly beta-hydroxybutyrate (PHB)
- Some bacteria contain gas for buoyancy and flotation.
- Granules: structures that contain crystals of inorganic compounds not enclosed in a membrane.
- Can be important for nucleic acid and ATP synthesis.
- Also termed metachromatic granules due to staining characteristic with methylene blue.
- Endospores
- Resting, dormant cells.
- Gram+ genera only: Clostridium & Bacillus and Sporosarcina.
- Vegatative cell & an endospore stage.
- Sporulation: formation of endospores.
- Germination: return to vegetative growth.
- Toughest of all life forms.
- Withstand extremes in heat, drying, freezing, radiation chemicals.
- Not reproduction.
- Resistance link to Calcium++ & dipicolinic acid and very thick coat.
- Dehydrated, metabolically inactive.
- Almost immortal? ...25, 250 million years.
- Only destroyed by pressurized steam at 120 degrees C for 20-30.
- Medical Significane of Endospores
- B. anthracis
- C. tetani (tetanus), botulinum (botulism) perfringens (gas gangrene).
Reference: https://sites.google.com/site/rccmicrobiology/chapter-4-procaryotic-profiles