Bacterial Structure, Function and Growth Flashcards
About how big are bacteria? (in microns)
0.2 μm – 10 μm
RBC’s are like 7 um
What are the two sugars in the rigid mesh peptidoglycan layer?
N-acetylglucosamine (GlcNAc) aka NAG
N-acetylmuramic acid (MurNAc) NAM
momma NAGs you when you eat’NAM proteo-sugaz
What are the major differences between gram + and - bacteria?
Positive:
Has Puffier Peptidoglycan wall + teichoic acid + lipoteichoic acid
Negative:
Two membranes. Not as much peptidoglycan layer in between (periplasmic space). Lipopolysaccharide chains. Porins. LIPOPROTEIN (anchors OM to peptidoglycan)
Why is the peptidoglycan layer important?
Usually required for strength and rigidity against osmotic forces
□ Targeted by antibiotics
□ Recognized by host innate resistant mechanisms
-Phagocytosis, complement, inflammation, direct killing by lysozyme
How is the peptidoglycan layer assembled?
MurNAc is linked to 5 glycine chain which is cross-linked from one chain (via DAP in gram-negative bacteria or L-lys in gram-positive bacteria) to D-ala on another chain
-Targeted by vancomycin (D-alanine residues)
What do you call the firmly attached, gelatinous, and usually complex polysaccharides that coat the surface of individual bacteria?
Capsule
How do capsules increase virulence?
Resist phagocytosis
**Protein-capsular polysccharide conjugate vaccine used in kids
(Back to LPS because it is in 4 slides)
What are the components of the most common lipid of the outer membrane: Lipopolysaccharide, aka Endotoxin?
- Lipid A
- Core polysaccharide, and
- O side-chain oligosaccharides that function as somatic antigens (O antigen)
What is the toxic component of LPS (endotoxin)?
Lipid A
It induces TNF and IL-1
What are the functions of the teichoic acids on Gram (+)?
Covalently linked to PG layer
Functions:
- Ion homeostasis
- Adherence an colonization
- Interacts with innate immune system through TLR
- Lipoteichoic acids help to anchor the cell wall to the membrane
What does the extracellular glycocalyx do?
Formation of biofilm “slime layer”
How does the biofilm help bacteria? (can you give 3 reasons)
- Allows the bacteria to adhere to surfaces like rocks, teeth, catheters, host cells, other bacteria
- Protects cells from phagocytosis, host defensive proteins (complement, antibody, defensins)
- Serves to limit access of many antimicrobial agents to the embedded cells
What do flagella do?
- motility
- role in pathogenesis (phase variation)
- H-antigen of flagella are used to classify enteric bacteria
Which rotations, clockwise or counterclockwise, are used for the following:
1) Swimming (running)
2) tumbling
1) running = counterclockwise
2) tumbling = clockwise (clock hands make tumbling motion)
What are pili used for?
- adherence to cells/ tissue
- conjugation (sex pillus)
Bacteria Use Multiple Secretion Systems to:
- Deliver Proteins to the Cell Surface,
- Assemble Organelles on the Cell Surface,
- Export Proteins to the Extracellular Milieu,
- Inject Proteins or DNA Into host Cells!
>Type III, IV, VI
What is the purpose of the cytoplasmic membrane
anatomical and physiological barrier between the inside and outside of the bacterial cell
Correctly name the four phases of bacterial growth in order
- Lag phase
- exponential phase
- stationary phase
- death phase
In what phase are bacteria most resistant to antibiotics?
Stationary phase:
- because penicillin or other β-lactam antibiotics act on growing cells.
- In nature, bacteria probably spend most of their time in stationary phase.
How many bacteria do you need to have to see turbidity? (cloudiness)
greater than 10^7/mL
What are the two forms of energy currency?
ATP (biosynthetic interconversions)
PMF ( Proton Motor Force: flagellar rotation, membrane transport)
Bacteria also require “reducing power” in the form of NAD(P)H
How do bacteria generate ATP and NADH? How are these processes different?
- Fermentation: organic compounds serve as both electron donor and electron acceptor
- Respiration: terminal electron acceptor is (typically) molecular oxygen
What enzyme interconverts ATP and PMF?
membrane ATPase
How do antimicrobials work on the principle of selective toxicity?
Select for components unique to bacteria, or concentrations that will affect bacteria and not host
What’s the difference between the following:
- indifferent anaerobes
- facultative anaerobes
- microaerophilic bacteria
- indifferent anaerobes: ferment with or w/o oxygen present
- facultative anaerobes: respires with O2, ferments w/o O2
- microaerophilic bacteria: grows best at low O2 concentrations and can’t grow without it
List some of the principal targets for the major groups of antibiotics used in human medicine.
- Cell wall antimicrobials
- Outer and cytoplasmic membrane antimicrobials
- Inhibitors of protein synthesis at the ribosomal level
- Inhibitors of nucleic acid synthesis
- Metabolic inhibitory antimicrobials
