Bacterial Structure Flashcards
Name the types of differential staining.
Gram stain, acid fast stain
What is a gram stain?
A differential stain based on chemical differences in cell wall structure, particularly on the thickness of peptidoglycan layer and presence of outer membrane.
What is the primary stain of the gram stain?
Crystal violet; Stains all bacteria purple.
What is Mordant?
It complexes with crystal violet to forma a large aggregate within heat fixed cells; Iodine in gram stains.
What is decolorizer?
Usually alcohol or alcohol-acetone; Removes stain complex from gram negative cells but not gram positive cells; Alcohol in gram stain
What does Counterstain do?
Stains decolorized cells pink; safranin in gram stain.
What is an acid fast stain?
A differential stain that binds strongly to bacteria that have waxy material in the cell walls; Used especially for Mycobacterium species. Acid-fast bacteria stain red; all others are blue
Name the major criteria for grouping bacteria?
Cell structure, Differential staining, Oxygen requirements, Endospore formation, and motility
What is in prokaryotic cells?
Cytoplasm, CM, Cell wall, outer membrane (Gram -), sometimes flagella, NO nucleus or organelles
Describe the prokaryotic cytosol.
Where most metabolic reactions take place, Ribosomes of 50s and 30s subunits; Coupled transcription and translation. A single circular chromosome with dsDNA; Super coiled by gyrase. May have plasmids that replicate independently of the chromosome.
Describe the Prokaryotic CM
Responsible for respiration; Contains a phospholipid bilayer but doesn’t contain sterols. The location of ETC and ATP synthase. Makes cell walls and secrets enzymes and toxins. Also contains chemotactic receptors.
Describe the Prokaryotic capsule
Hydrophillic layer around cell; Outside the outermost layer of cell wall. Not unique to either Gram positive or Gram negative. Usually a sugar and antigenic. An important virulence factor; Anti-phagocytic, Adhesin and invasin.
Describe the Prokaryotic cell wall
Rigid, gives shape to cell. PREVENTS OSMOTIC RUPTURE of the cell. Reacts with gram stain. Contains peptidoglycan; Unique to prokaryotes.
What is peptidoglycan?
A polymer only found in prokaryotes; Anti-phagocytic, Mitogenic, and pyrogenic. It is a linear chain of two alternating sugars with peptide crosslinks making one covalent molecule; Sugars are N-acetylglucosamine and N-acetylmuramic acid. Muramic acid is only found in peptidoglycan.
Describe peptiodglycan
Attached to each muramic acid residue is a peptide chain; Contains D-amino acids and diaminopimelic acid.
What role does lysozyme play in relation to peptidoglycan?
Lysozyme (found in tears and mucuos), degrades peptidoglycan by hydrolyzing the glycan chain. Many antibiotics block steps in PG synthesis.
What happens to crystal violet dye when in contact with gram positive and gram negative bacteria?
Gram positive cells retain the dye and turn purple. Gram negative cells lose the dye during decolorization and must be counterstained to be seen; Will turn pink
Describe gram positive cell envelope
A thick 3D layer of peptidoglycan anchored to the cytoplamsic membrane by lipoteichoic acid.
What is teichoic acid?
Unique to gram positive cells. A polymer of glycerol phosphate or ribitol phosphate; Covalently linked to muramic acid of peptidoglycan.
Describe gram negative cell envelope.
Thin layer of peptidoglycan thats between inner and outer membranes; Also called the periplasmic space. This spaces contains hydrolytic enzymes and chaperones. Peptidoglycan linked to OM by lipoprotein called Braun’s lipoprotein. OM contains lipopolysaccharide.
Describe the gram negative outer membrane.
An asymmetric bilayer; Inner leaflet is made of phospholipids. Outer leaflet is made of LPS. Contains porins, host interactiion proteins and secretion systems.
What is lipopolysaccharide (LPS)?
Toxic to most animals; Causes inflammatory response ?and endotoxic shock. Major virulence factor in gram negative bacteremia (sepsis). Present in all gram negative bacteria and not present in gram positive.
What is LPS made of?
- Lipid A: Phosphorylated glucosamine disaccharide to which fatty acids are attached; Toxic & very hydrophobic.
- Core Polysaccharide: 3 KDO residues and sugar residues
- O antigen: Highly variable; Hydrophillic and can act as a surface antigen of many gram negative cells. (Smooth LPS has no O-antigen)
Describe flagella
Long helical protein filaments that rotate to provide motility. Powered by proton gradient. Contains a basal body, hook and flagellin polymer filament. Number and location of flagella vary.
What is the primary stain, decolorizer and counterstain in acid fast staining?
Primarty stain: Hot Carbolfuschin
Decolorizer: Acid alcohol
Counterstain: Methylene blue
Describe peptidoglycan biosyn
thesis.
- Synthesis of muramic acid (pentapeptide)
- Addition of NAG at CM
- Addition of precursor to growing glycan chain by transglycosylases (On cell surface).
- Crosslinking between peptides of other glycan chains (transpeptidases).
