Lecture 7: Bacterial Cell Shape
No description yet. This curated deck is ready for daily study.
Card preview (19)
What is the average size of bacteria?
0.2-1um x 2-8um
What are the 3 basic bacterial shapes?
• Spherical • Rod • Spiral
What are some unusual bacterial cell shapes?
• Star-shaped ‘stella’ 2. Square ‘haloarcula’
What does monomorphic mean?
having or existing in only one form (most bacteria)
What does pleomorphic mean?
Occurring in various distinct forms (least common)
What is the term used for pairs of bacteria?
Diplococci (spherical), diplobacilli (rod)
What is the term used for clusters of bacteria?
staphylococci (spherical)
What is the term used for chains of bacteria?
streptococci (spherical), streptobacilli (rod)
What determines bacterial cell shape
• cell wall (exoskeleton) a. strip cell wall -> spheroplast/protoplast b. genes involved in cell wall synthesis • cytoskeleton (different to eukaryotic)
What does the bacterial cell wall do?
• size • shape • prevent osmotic lysis
what does peptidoglycan do?
rigidity for bacterial cell walls
What is peptidoglycan?
• Backbone of alternating sugars (dimer) a. N-acetylglucosamine (NAG) b. N=acetylmuramic acid (NAM) - unique c. cross links occur between back bones i. direct bonds ii. pentapeptide side chains • Amino acid side chains on NAM a. D amino acids b. Diaminopimelic acid (DAP)
Explain the Gram-positive cell wall
• thick peptidoglycan (60-90%) • Interwoven teichoic acids (acidic polysaccharides) • Surface studed with proteins • no lipids • molecules freely pass through peptidoglycan so they do not get trapped unless tethered to csm or wall
Explain the Gram-negative cell wall
• Two layers: thin peptidoglycan (10-20%), Outer membrane (permeability barrier) • Periplasm - gelatinous material between; outer membrane, peptidoglycan and cytoplasmic membrane (contains proteins needed for transport of materials to and from cells)
Explain the outer membrane of bacteria
• phospholipid bilayer • Lipopolysaccharide (LPS): LipidA portion embedded in outer membrane, polysaccharide extends outward from surface • Surface of membrane is studded with proteins • semipermeable with porins • ONLY IN GRAM NEGATIVE
What bacteria have Atypical cell walls?
• Mycobacterium 2. Nocardia
What is the structure of Atypical cell walls?
• Gram-positive cell wall structure with lipid mycolic acid a. pathogenicity + high resistance to certain chemicals and dyes b. basis for acid-fast stain used for diagnosis of infections cause by these microorganisms • Some have no cell wall - Mycoplasma a. cell wall stabilized by sterols b. pleomorphic c. ie., no peptidoglycan
How do archaeal cell walls differ from bacterial cell walls?
• no peptidoglycan • pesudo-peptidoglycan instead: • instead of NAM archaea have: a. N-acetyl talosaminuronic acid (NAT) b. No D-amino acids
How do cell walls grow?
• NAM and NAG synthesis in cytoplasm a. attached to membrane carrier molecule ‘bactoprenol’ b. transported across cell membrane • links in peptidoglycan have to be broken a. AUTOLYSINS: break glyosidic bonds and peptide cross-bridges • New peptidoglycan monomers (NAM- NAG dimer) inserted a. TRANSGLYCOSIDASE enzymes • Peptide crosslinks resealed a. TRANSPEPTIDASE enzymes: penicillin binding proteins - PBPs