Microbiology Ch 2 Flashcards
Compare and contrast the cell membranes of Bacteria and Archaea?
Likes: phospholipid bilayer; glycerol and phosphate are part of the phospholipid bilayer
Bacteria:
- cell membrane is a lipid bilayer
- Contains fatty acids
Archaea
- lipid bilayer or a monolayer
- isoprenes (phytanyl) instead of fatty acids
- ether linkages instead of ester linkages
- can fuse together to form a lipid monolayer
Describe the major functions of the prokaryotic cell membrane?
Selective, semipermeable barrier
- That protects the intracellular environment from the extracellular ( only allows certain molecules in)
Protein Anchor
- Polar and charged molecules must be transported, bind the cell membrane to other structures. Transported proteins accumulate solutes against the concentration gradient
Energy conservation and transformation
- Generation of proton motive force (motility, photosynthesis and respiration)
Bacterial cell wall
The bacterial cell wall is a complex, mesh-like structure that in most bacteria is essential for maintenance of cell shape and structural integrity
Structure
- peptidoglycan: rigid layer in the cell wall that is primarily responsible for the strength of the wall
Gram-positive cell envelope
- 2 components: plasma membrane + thick cell wall + outer membrane
- Gram stain: stained purple
- Contains wall
- teichoic (links the peptidoglycan layers)
- lipoteichoic acid (links cell wall to plasma membrane) - Thick cell wall helps prevent desiccation
Gram-negative cell envelope
- 3 components: plasma membrane + thin cell wall + outer membrane
- Gram stain: cells are red
- lipopolysaccharide- endotoxins component - (Lipid A) toxic to other cells if dies
Acid-fast Cell wall (atypical)
- Similar to GPB structure
- Possess an outer lipid layer made of waxy lipids (mycolic acid)
- highly resistant to disinfectants and dry conditions
Archaeal cell wall
- if present, thin cell wall (not made up of PG)
- Made of polysaccharides
- lack outer membrane
- No Gram stain
- Nearly all have s-layer
Glycocalyx (Bacteria)
- Surrounds the cell wall of the membrane of bacteria (out most layer of cells)
- Network of polysaccharide chains of membrane proteins and lipids.
- Function: Attachment of cells to surface and other cells
S layer (Arches and Bacteria)
- Found in Archaea and many bacteria
- Paracrystalline structure consisting of protein or glycoprotein
- Outermost layer of the cell envelope
Functions: - Protects cells from host defenses (phagocytosis)
- Protects cells from viruses
- Protection from lysis
- Confers structural strength
Capsules (Glycocalyx) (Bacteria)
- neatly organized, firmly attached (covalent), helps define cell boundaries,
- Composed of polysaccharide (organized and repeating units
- Prevents bacteria from being recognized and engulfed by host
- function: collect nutrients from it’s surroundings, protects against dehydration, attaches to other cells
- Capsule: polysaccharide coating
Slime layer (bacteria)
- unorganized and loosely attached (non covalent)
- complex mixture of polymers, including polysaccharides, polypeptides and extracellular DNA
- water soluble
Pili (including Fimbriae) (Bacteria)
- non-flagellar, proteinaceous, multi-subunit surface appendages involved in adhesion to other bacteria, host cells, or environmental surfaces
- spikes that form on the side of bacteria
- Fimbriae- hair like structures along side Pili that help with bacteria adhesion
Flagella (bacteria)
- large whip-like appendages that confer motility and assists in motility
- increase and decrease rotational speed relative to strength of proton motive force
Structure:- Filament: composed of flagellin protein
- Hook: connects filament to basal body
- Basal Body (motor): anchored through the cell envelope, in contact with cytoplasm
Movement- rotation and ion-movement force
Archaella (Archea)
- unique structure on the cell surface of many archaea, that allows for mobility
-Movement: rotation and APT - thinner than bacteria flagella
- smaller diameter, not hollow (solid), motor fewer proteins
Explain the Gram stain procedure and mechanism?
- A differential stain that differentiates between bacteria with different cell-wall structure
- Primary stain: crystal violet (CV) all cells stained purple
- Mordant: wash off to remove excess CV and smear with iodine
- Decolorizing agent: wash slides with alcohol, purple color remains in GPB and GNB colorless
- ## Counter stain: wash off alcohol and stain with secondary stain, GNB turns red
