CH 3c outer structures and gram staining Flashcards
CH 3c
Outer membrane
Gram negative bacteria only
Porin protein channel - transport of small molecules
Specialized receptors - transport of large molecules
Considered to be part of the wall, it’s very toxic
CH 3c
Cell wall
Outside of plasma membrane (in G-neg bacteria, it’s between the two membranes)
Functions:
- cell structure and shape
- prevents osmotic lysis
- protection against toxic substances
- contributes to pathogenesis
Mycoplasma lacks typical cell wall (pleomorphic)
CH 3c
Cell wall: Gram-negative v. Gram-positive
G-positive: thick layer of peptidoglycan
Gram-negative: thin layer of peptidoglycan; outer membrane
CH 3c
Peptidoglycan
Backbone: basic chain of alternating sugars (NAM and NAG)
Short peptide chain of four D and L alternating amino acids off of the NAM sugar
Backbone forms a helix with cross links between the peptide chains - forms 3D structure of cell walls. (peptide bonds between 4th amino acids)
Gram-negative links directly between amino acids, making a tighter scaffold and denser cell wall.
Gram-positive links using a glycine bridge, making for a looser scaffold.
CH 3c
Gram-positive cell walls
Could have up to 17 layers of peptidoglycan. No outer membrane. Unique acids: - teichoic acids (peptidoglycan layer) - lipoteichoic acids (membrane)
CH 3c
Teichoic acids
Can be formed using glycerol or ribitol sugars. joined by phosphate groups
Not really sure about the function… maybe for protection from other cells or used as an anchor to a flat surface?
gives cell wall negative charge
CH 3c
Gram-negative cell walls
Smaller peptidoglycan layer, outer membrane
- space between inner membrane and outer membrane is called the periplasmic space (like a screen porch) - it’s a functional space that extends the usable surface area of the cell
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CH 3c
Periplasmic space
space between plasma membrane and outer membrane for gram negative and pm and cell in in gram positive bacteria. can have proteins, help with nutrient transport, metabolic funcitons
CH 3c
Gram-negative behavior b/c of the outer membrane
G-neg cells’ outer membrane has many different macromolecules that have a variety of functions and cause Gram-negative bacteria to have different behaviors/ characteristics.
CH 3c
Outer membrane macromolecules
Lipopolysaccharides
Porin transport proteins–aidin permeability
Braun’s lipoproteins–attaches outer membrane to cell wall
CH 3c
Lipopolysaccharides (LPS)
Make up the outside layer of the outer membrane's bilayer. Lipids attached to complex sugar molecules. Three components: O antigen Core region Lipid A
CH 3c
Lipopolysaccharides - O antingen
Very unique - variation even within species, unique to the strain of that species
Hydrophilic
What human antibodies recognize and target (hence name “antigen) - some species adapt very quickly, however, and can change their O antigens faster than our immune systems can register and fight them.
Also help regulate what enters the cell - bent chains form a kind of shield that prevents unwanted chemicals from entering.
CH 3c
Lipopolysaccharides - core region
Composed of sugars - not much variation between species
CH 3c
Lipopolysaccharides - Lipid A
Hydrophobic
Phosphorylated sugar head group with multiple fatty acid tails
Responsible for toxic effects of LPS - cause inflammatory response; funnily, as long as the bacteria is alive and its outer membrane is intact, we’re not exposed to the Lipid A, but when they die and break apart is when we’re exposed to the Lipid A toxin.
CH 3c
Porin proteins
Transport proteins that are very specialized.
CH 3c
Braun’s lipoproteins
Anchors outer membrane to the cell wall.
CH 3c
Cell Wall of bacteria as a Target
Bacterial cell walls act as protection from lysis due to osmotic pressure - there are many natural and manufactured defenses that target the cell wall in order to kill the bacteria.
Lysozyme
Penicillin
Both are more effective against Gram-positive bacteria than Gram-negative because the G-pos cell wall is exposed while the G-neg cell wall is protected by the outer membrane.
CH 3c
Lysozyme
Natural defense mechanism that kills bacteria by breaking apart the glycosidic linkages between NAM and NAG (backbone of cell wall).
Found in human tears and saliva (entry points to the body) - also found in chicken eggs.
CH 3c
Penicillin
Inhibits formation of crosslinks between peptide chains in cell wall.
CH 3c
Gram stain procedure
It’s a differential stain - divides bacteria into groups based on their reaction to the stain. Is it G-pos or neg? Pos = purple; Neg = pink
- Stain all cells with Crystal Violet
- Iodine treatment - I binds to CV, forming large molecules
- Decolorization - use alcohol to remove stain
- Counter stain with Safranin (pink dye). Gram-negative are pink while Gram-positive are still purple from the Crystal Violet stain.
CH 3c
Why is the decolorization step in the Gram staining procedure so important?
allow you to ID bacteria as either G-neg or G-pos. Because G-neg bacteria have a much thinner cell wall, the large complex formed by the Crystal Violet stain and the iodine will be able to leave the cell, making the bacteria clear (it will show up as pink after the additional staining in the fourth step).
The cell walls of G-pos bacteria are much thicker, so the large CV-I complex can’t get out of the cell, leaving it purple even after the additional staining in step four.
CH 3c
Glycocalyx
Also known as a capsule or slime layer.
Very thick, dense, and organized.
Generally composed of polysaccharides.
attachment
CH 3c
Capsule
Function:
- resist phagocytosis
- resist desiccation
- exclude bacteriophages (viruses that attack bacteria)
- adherence*** (allow them to stick to mucous membranes and cause illness rather than being washed away, and avoid phagocytosis bc macrophage can’t get around it) Make pathogenic bacteria more pathogenic - it’s a virulence factor
CH 3c
Capsules/ slime layers as a virulence factor
Adherence of bacteria to surfaces (rather than being washed away) makes pathogenic bacteria more pathogenic. w00t…
CH 3c
Slime layer
More diffuse than a capsule
Easily removed
Same functions as capsule + gliding motility
CH 3c
S layers
Structured layer of protein or glycoprotein - protective layer outside of bacteria Autocatalytic formation Maintains cell shape/ rigidity Aids in attachment to surface Protection
- ion and pH fluctuation
- osmotic stress
- enzyme activity (protects against)
- predatory bacteria
CH 3c
Autocatalytic formation
proteins only need to be present and they form correct structure on their own - interesting properties for research
