What are the differences in membrane lipids and mRNA between eukaryotes, archaea, and bacteria?
- Bacteria and Eukaryotes: ester-linked straight chain fatty acids
- Archaea: ether-linked branched aliphatic acids
- Bacteria and Archaea have polycistronic mRNA
- Eukaryotes do mRNA splicing, capping, and poly A tail
Do bacterial cell walls contain sterols?
No cholesterol or sterols except Mycoplasma because they steal sterols from host
What are the components of peptidoglycan?
- Glycan strands: repeating NAM and NAG, beta 1,4 linkage
- Peptide crosslinks: 5 residue peptide linked to NAM also linked to each other at 3,4 residues
- Use of D-form AA that are not encoded from mRNA, but from enzymes
What are the steps to Peptidoglycan synthesis?
- 1. Activate NAM & NAG with UDP carrier (UDP-NAM made from UDP-NAG)
- 2. Polymerize stem peptides on UDP-NAM (UDP-NAM-PEP = Park’s nucleotide)
- 3. Load lipid (bactoprenol phosphate) and add UDP-NAG
- 4. Flip across membrane & join existing peptidoglycan
- 5. Crosslink step peptides with transpeptidases
What are the enzymes of peptidoglycan synthesis?
- PBPs (penicillin binding proteins)
- They are the transglycosylase and transpeptidase enzymes
- Most bacteria have at least 4 and they are numbered in order of decreasing MW
- They are targeted by Penicillin (a beta lactam)
How do beta-lactams like penicillin kill bacteria?
- It disrupts the cell membrane by binding to the transglycosylase and transpeptidase enzymes of peptidoglycan synthesis
- It mimics the D-Ala-D-Ala terminus of stem peptides, when bound it is acylated and irreversibly inactivates the enzymes
- Cell wall synthesis slows and degradation continues so the bacteria dies
- Works best on gram +
How do glycopeptides like vancomycin kill bacteria?
- They are large antibiotics that can bind the D-ala-D-ala terminus of stem peptides
- This stops transpeptidation (because stem peptides are bound)
- Only works with gram + bacteria, the large molecules can’t cross the outer membrane of gram –
What is in Teichoic Acid?
- It is a polymer of ribol or glycerol with linked choline, D amino acids or sugars
- It is negatively charged
- Lipoteichoic acid also has a fatty acid component attached to the cytoplasmic membrane
In gram – bacteria is the outer leaflet hydrophobic or hydrophilic?
- The outer leaflet is hydrophilic, but the inner leaflet is hydrophobic (think the inner leaflet is hiding from the water)
- This allows the bacteria to be relatively impermeable to both types of molecules
- Porin channels are used to transport nutrients
What components make up the Mycobacterium cell wall and how is it identified?
- They have a high concentration of lipid material at cell surface (more that 50% is mycolic acids)
- The high concentration of high molecular weight fatty acids (mycolic acid has between 50-90 carbons) allows an acid fast stain to be used to identify them
What three roles do somatic bacterial pili play in virulence?
- Adhesion to host cells with adhesins on the tips of the pili
- Immune escape (alter pili antigenicity)
- Inhibit complement
How do pili play a role in how uropathogenic E. coli (UPEC) attacks people?
- If UPEC expresses P-pilus it binds galactose in uroepithelial mucosa in renal tissue (pyelonephritis)
- If UPEC expresses type 1 Pilus, it binds mannose on Uroplakin Ia in bladder (cystitis)
What is the difference between bacterial and eukaryotic flagella?
- Eukaryotic flagella (example on sperm) are similar to cilia and whip back and forth
- Bacterial flagella have a rotary motor that can spin both clockwise and counter clockwise, counter-clockwise propels bacteria forwards, clockwise causes it to tumble
One flagellum at a pole
one tuft of flagella at pole
flagella at both poles
flagella all around the cell
What two types of bacteria produce spores?
Clostridium and Bacillus
What are the five layers of a spore?
- Exosporum – membrane
- Coat(s) – keratin-like protein with S-S bonds
- Cortex – concentric rings of peptidoglycan
- Inner membrane – similar to cytoplasmic membrane
- Core – contains DNA and enzymes (no mRNA) also contains dipicolinic acid (DPA) which crosslinks with spore proteins for heat / radiation protection
How does the antibiotic cycloserine kill bacteria?
It competitively inhibits enzymes in the cytoplasm responsible for assembling the D-ala-D-ala dipeptide prior to its incorporation into peptidoglycan
What is the toxic component of endotoxin?
The fatty acids of lipid A