Lecture3 Peptidoglycan synthesis and Eukaryotic Cell structure Flashcards
Gram-postive bacteria stain ____
purple
Gam-negative bacteria stain ____
pink
Giemsa staining is due to
cell wall structure
What two alternating sugars for peptidoglycan backbone
- N-acetylglucosamine (NAG)
- N-acetylmuramic acid (NAM)
Peptidoglycan chains have alternating ___ and ____ amino acids attached to ____
D-, L-, attached to NAM
Peptidoglycan is joined by crosslinks between the _____
peptides
E. coli peptidoglycan exhibits _____ cross-linking
direct
Staphylococcus aureus peptidoglycan exhibits _______ linking
Peptide interbridge
Peptidoglycan synthesis is a complex process involving _____ derivatives
UDP
Peptidoglycan synthesis uses ____ to transport NAG-NAM- pentapeptide units across the cell membrane
bactoprenol
Function of Bacitracin
Does not allow bactroprenol carrier to lose one phosphate (bactoprenol phosphate) and move back to the cytoplasmic side of the membrane
The final step in peptidoglycan synthesis is _____which creates the peptide cross-links between the peptidoglycan chains
transpeptidation
Amino acids are added to NAM one at a time, except for the last _____ ____, which are added in the same reaction
D-alanines
What are the two carriers involved in peptidoglycan biosynthesis
- Bactoprenol
- Uridine diphosphate
A 55-carbon alcohol that attaches to NAM by a pyrophosphate group and moves peptidoglycan units through membrane
Bactoprenol
Bactoprenol is a ___- carbon alcohol that attaches to NAM by a _____ group
55, pyrophosphate group
Bactoprenol function
moves peptidoglycan units through hydrophobic membrane
Uridine diphosphate is an activated ______ carrier, except in the case of peptidoglycan synthesis it carries _____ or ____ instead of glucose
sugar, NAM or NAG
Cycloserine inhibits
Blocks formation of D-Ala-D-Ala
______ inhibits transpeptidation by binding to D-Ala-D-Ala
Vancomycin
Penicillin inhibits the ______ reaction
transpeptidation
_____ blocks the dephosphorylation of bactoprenol pyrophosphate
Bacitracin
The 8 stages of peptidoglycan synthesis
- UDP derivatives of NAM and NAG are synthesized in the cytoplasm
- Amino Acids are added sequentially to UDP-NAM to form the pentapeptide chain
- The 2 terminal D-alanines are added as a dipeptide
- No ribosomes involved - NAM-Pentapeptide is transferred from UDP to a bactoprenol phosphate at the membrane surface
- UDP-NAG adds NAG to the NAM-pentapeptide
- Glycine interbridge, if present, is added - The completed unit is transported across the membrane to its outer surface by the bactoprenol pyrophosphate carrier
- The peptidoglycan unit is attached to the growing end of a peptidoglycan chain
- Bactoprenol returns to inside of membrane. A phosphate is released; bactoprenol phosphate can now accept another NAM-pentapeptide
- Transpeptidation occurs
How does a bacterial cell add new peptidoglycan units to its existing cell wall
- Autolysis carry out limited digestion of peptidoglycan
- This provides acceptor ends for addition of new peptidoglycan units
are ribosomes involved in the amino acids being added sequentially to UDP-NAm to form the pentapeptide chain
No!
Gram-positive bacteria stain
purple
Gram-negative bacteria stain
pink
The gram staining reaction is due to
cell wall structure
Inventor of gram stain
Danish physician Hans christian Gram
The gram stain was invented in ____ and published in
1883 and published in 1884
Hans Christian Gram studied ____ tissue sections form patients who died of ____
lung, pneumonia
Han Christian Gram discovered that _____ and a solution of ___ and ____ formed a water soluble precipitate that could be removed from host tissues and some microbial cells by an alcohol rinse. Many other microbes retained the stain
Gentian (crystal) violet, iodine, and potassium iodide
Hans Cristian Gram did not originally use ____ in his stain
safranin
Gram stain primary stain is _____ in combination with ___.
- Crystal violet in combination with iodine
What is the function of iodine in the gram stain
it acts as a mordant to enhance crystal violet staining
What is the counter stain used in gram staining
Safranin
What is used to decolorize the gram negative bacteria
Alcohol or acetone removes crystal violet from Gram-negative cells
Gram-positive cell wall has a ___ ring basal body
2
Gram-negative cell wall has a ___ ring basal body
4
Gram-positive cell wall is disrupted by ____ and sensitive to ____
lysozyme, Penicillin
Gram-negative cell wall is _____ sensitive
Tetracycline (because it attacks the ribosomes)
Acid-fast cells resist decolorization with _____
acid alcohol
the basis for acid-fast staining is a ____ cell wall composed of ______
waxy cell wall composed of mycolic acids
examples of cells that stain with acid-fast stain
- Mycobacterium
- Nocardia
The waxy cell wall composed of mycelia acids prevents
water-soluble stains form crossing the cell wall
Acid-fast staining methods use ______, which is a ______ soluble stain
carbolfuchsin, lipid soluble stain
Acid-fast stain ,Carbolfuchsin, contains ____ to help the stain penetrate the cell wall
Phenol
Acid-fast cells often give ____ gram stain results, this is due to
abnormal, poor stain absorption followed by high retention
Acid fast staining is important for identifying bacteria in the genus _____, which can be pathogenic
Mycobacterium
Examples of bacteria in the genus Mycobacterium
- M. leprae
- leprosy
- M. tuberculosis
- Tuberculosis
Acid fast staining can be used to identify opportunistic pathogenic members of the actinomycete genus _____ and oocysts of coccidian parasites, such as _______ and _____
Norcardia, Cryptosporidium, Isospora
bacterial spores are _____, as well as the head of sperm, and certain eukaryotic cellular inclusions (neuronal cytoplasmic inclusion bodies and nuclear inclusion bodies)
acid fast
What is a common counterstain in acid fast staining
methylene blue