Lecture 3 Flashcards
What makes up a polyribosome?
Ribosomes attach to single mRNA molecules
What is the function of polyribosomes?
coupling transcription and translation
Is E. coli gram positive or negative?
negative
Which (+/-) has a thick cell wall made of peptidoglycan? what does this prevent?
Gram-positive, limits the passage of hydrophobic compounds
What is another name for peptidoglycan?
murein
Which (+/-) has teichoic and lipoteichoic acids?
Gram-positive
Which (+/-) has an outer membrane made of lipopolysaccharide (LPS)?
Gram-negative
Gram’s method used what as the primary stain?
Crystal Violet
Gram used what as a mordant?
iodine
Gram used what as a decolorizer?
ethanol
What is the Gram Stain Procedure?
1) stain with crystal violet (purple); wash
2) mordant (bind) the dye with potassium iodide; wash
3) flush with alcohol; wash. Gram-negative bacteria are decolorized; Gram-positive bacteria remain purple
4) counterstain with safranin (red); wash. Gram-negative bacteria become red; Gram-positive bacteria remain purple.
What does the amphipathic nature of phospholipids allow?
self assembly
What helps protect against osmotic stress?
cell wall
What 4 functions do proteins in the cell membrane do?
1) respiration and photosynthesis
2) nutrient uptake
3) appendages
4) signaling
What are the glycan chains made up?
alternating N-Acetylglucosamine (NAG) and N-Acetylmuramic acid (NAM)
What is peptidoglycan made of?
NAG (GlcNAc) and NAM (MurNAc)
What type of bonds are NAG and NAM connected by?
beta (1,4) glycosidic bonds
Which is the peptide chain attached to?
NAM
What is DAP?
diaminopimelic acid, a derivative of lysine
What are the crosslinks between peptidoglycan in Gram-?
DAP and D-Ala
What are the crosslinks between peptidoglycan in Gram+?
L-Lys and D-Ala
Where is DAP only found in?
Gram-
Where is Lysine only found in?
Gram+
What are teichoic acids made of?
chains of glycerol phosphate or ribitol phosphate linked by phosphodiester bonds
Where do teichoic acids connect?
peptidoglycan or cell membrane
Function of teichoic acids?
give rigidity to cell wall, and promote adherence of bacteria to specific surfaces
How are wall teichoic acids linked to PG?
covalently, vis phosphodiester bond to C6-hydroxyl of NAM
Where are lipid teichoic acids anchored?
cell membrane via glycolipid and a glycerol phosphate
LPS has what type of leaflets?
inner and outer
What are the 3 parts that make up the LPS?
1) lipid A — amphipathic
2) core polysaccharide
3) o-antigen
What is Lipid A made of?
short chain of fatty acids attached to a disaccharide
What is another name for Lipid A? why?
endotoxin, b/c can indue toxic shock
What is the core polysaccharide made of?
2 sugars: keto-deoxyocatanoic acid and heptose
What is the O-antigen made of?
long carbohydrate chain (40 sugars_
What is the role of the O-antigen?
creates a polar barrier which is important for bile salt and antibiotic resistance
What are 2 key points about the O-antigen?
1) variable and specific to organism
2) high immunogenic
How does the LPS affect nutrient uptake and growth?
slows both of them down
How does Gram- bacteria counteract the effect of the LPS?
they have many channel proteins = porins
How big does a molecule have to be to need a special transporter?
larger than a trisaccharide
What type of bacteria (+ or -) can vancomycin be used against? why?
only Gram- b/c it can’t pass through the outer membrane porins
What type of bacteria (+ or -) can polymyxins be used against? why?
only Gram- b/c they specifically bind to LPS
Where is the periplasm found?
Gram-, between the inner and outer membrane
What happens in the periplasm? (3)
1) allows passage of enzymes across inner membrane
2) trap nutrients in cell
3) inactivates antibiotics
What has an acid-fast cell envelope?
mycobacterium tuberculosis and its relatives
What does the acid-fast cell envelope do?
it is so thick (lots of waxes called mycolic acids) that it makes the bacteria resistant to harsh chemicals (disinfectants and strong acids)
What does the acid-fast cell envelope prevent?
severely reduces nutrient uptake and growth rate
What are the steps to acid-fast stain? (3)
1) stain with hot fuchsin (red); wash
2) decolorize with acid alcohol; wash. only acid-fast bacteria remain red.
3) counterstain with methylene blue; wash. All other material becomes blue.
How can hot fuchsin stain be taken up?
brieft heating
How is the dye removed?
dilute HCl acid treatment
Why is the dye not removed from mycobacteria?
b/c waxy cell wall makes it resistant to acid
