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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
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Do bacterial cell walls contain sterols?
No cholesterol or sterols except Mycoplasma because they steal sterols from host
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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
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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
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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)
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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 +
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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 –
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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
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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
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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
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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
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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)
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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
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Define monotrichous
One flagellum at a pole
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Define lophotrichous
one tuft of flagella at pole
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Define amphitrichous
flagella at both poles
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Define Peritrichous
flagella all around the cell
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What two types of bacteria produce spores?
Clostridium and Bacillus
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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
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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
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What is the toxic component of endotoxin?
The fatty acids of lipid A
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