Lecture 4: Gram staining and Peptidoglycan Flashcards
What is the primary stain used in Gram staining?
Crystal violet
What role does Gram’s iodine play in Gram staining?
Binds crystal violet
What is the decolorizer used in Gram staining?
Acetone or ethanol
What color do Gram-positive bacteria appear after staining?
Purple
What color do Gram-negative bacteria appear after staining?
Pink
What is the secondary stain used in Gram staining?
Safranin
What color does safranin turn Gram-negative cells?
Red/pink
What are the two main components of peptidoglycan?
NAG and NAM
What does NAG stand for?
N-acetylglucosamine
What does NAM stand for?
N-acetylmuramic acid
List the amino acids found in the tetrapeptide of peptidoglycan.
- L-alanine
- D-glutamic acid
- meso-DAP (or L-lysine)
- D-alanine
What is the structure of peptidoglycan described as?
Very large molecule of repeating units
What forms the backbone of peptidoglycan?
Alternating NAG and NAM strands
What is attached to NAM in the structure of peptidoglycan?
Tetrapeptide (L-ala, D-glu, M-DAP, D-ala)
How are NAG/NAM strands cross-linked in peptidoglycan?
By covalent bonds between the tetrapeptides extending from each sugar strand
What additional feature does Gram-positive peptidoglycan have?
Peptide interbridge
What is the mode of action of penicillin?
Prevents cross-linking of adjacent glycan chains
Why is penicillin usually more effective against Gram-positive bacteria?
Outer membrane of Gram-negatives blocks access
What is a characteristic of penicillins?
They have β-lactam rings
What does the β-lactam ring bind to?
Enzymes that crosslink the peptidoglycan (tetrapeptides)
What is lysozyme?
An enzyme that targets peptidoglycan
Do penicillin and lysozyme affect Mycoplasma species?
No, they lack a cell wall
What do Mycoplasma species contain in their cytoplasmic membrane?
Sterols that increase strength
What is a defining characteristic of Archaea cell walls?
They vary widely and do not contain peptidoglycan
What is pseudopeptidoglycan?
A similar molecule to peptidoglycan found in some Archaea
What are S-layers in Archaea?
Built from sheets of flat protein or glycoprotein subunits
