1 Microbial Physiology Module 1: Cell wall

All are components of a Gram-negative cell wall except:

• Diaminopimelic Acid

• Peptidoglycan layer

• Teichoic acids

• Lipid A

Answer explanation

Option 1: Incorrect! (DPA is present in the Gram-negative bacteria in its meso-isomer form).

Option 2: Incorrect! (Both Gram-negative and Gram-positive cell walls have peptidoglycan layer).

Option 3: Correct! (Teichoic acids are specific polymers of glycerol or ribitol repeating units that are found in Gram-positive cell walls).

Option 4: Incorrect! (Lipid A is a component of the lipopolysaccharide layer of a Gram-negative cell wall).

References:

Kang, S., Sim, J., Yun, C., & Han, S. H. (2016). Lipoteichoic acids as a major virulence factor causing inflammatory responses via Toll-like receptor 2. Archives of Pharmacal Research, 39(11), 1519–1529. https://doi.org/10.1007/s12272-016-0804-y

Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A. (2018). Brock biology of microorganisms. Pearson Higher Education.

Which statement is true about archaeal cell wall?

• Glycan units consist of N-acetylmuramic acid

• Peptide bridge contains L-amino acids

• Glycan units are connected by beta 1-4 bonds

• None of the aforementioned

Answer explanation

Option 1: Incorrect! (Glycan units consist of N-acetyltalosaminuronic acid).

Option 2: Correct! (Peptide bridge contains L-amino acids rather than D-amino acids).

Option 3: Incorrect! (Glycan units are connected by beta 1-3 bonds).

Option 4: Incorrect! (Option 2 is correct).

References:

Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A. (2018). Brock biology of microorganisms. Pearson Higher Education.

Subedi, B. P., Martin, W. F., Carbone, V., Duin, E. C., Cronin, B., Sauter, J., Schofield, L. R., Sutherland-Smith, A. J., & Ronimus, R. S. (2021). Archaeal pseudomurein and bacterial murein cell wall biosynthesis share a common evolutionary ancestry. FEMS Microbes, 2. https://doi.org/10.1093/femsmc/xtab012

Which is not a characteristic of the peptidoglycan layer?

• It is a disaccharide polymer

• The repeating unit is called the glycan tetrapeptide

• The glucose residues are connected by beta 1-4 linkages

• It is a soluble and porous polymer

Answer explanation

Option 1: Incorrect! (This is a characteristic of a peptidoglycan layer. Peptidoglycan is a disaccharide polymer of N-acetylglucosamine and N-acetylmuramic acid linked by polypeptide).

Option 2: Incorrect! (This is a characteristic of a peptidoglycan layer).

Option 3: Incorrect! (This is a characteristic of a peptidoglycan layer).

Option 4: Correct! (Peptidoglycan is an insoluble and porous polymer).

References:

De Pedro, M. (2009). Peptidoglycan (Murein). In Elsevier eBooks (pp. 453–469). https://doi.org/10.1016/b978-012373944-5.00339-4

Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A. (2018). Brock biology of microorganisms. Pearson Higher Education.

In the transpeptidation reaction of peptidoglycan synthesis in Gram-negative bacteria, the displaced amino acid is:

• L-lysine

• D-glutamate

• D-alanine

• D-lysine

Answer explanation

Option 3: Correct! (In gram-negative bacteria, formation of the peptidoglycan cross-link is via a peptide bond from the amino group of DAP of one glycan chain to the carboxyl group of the terminal D-alanine on the adjacent glycan chain. The transpeptidation reaction involves nucleophilic displacement wherein the nucleophilic N attacks the carbonyl, displacing the terminal D-alanine.

References:

Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A. (2018). Brock biology of microorganisms. Pearson Higher Education.

 

White, D., Drummond, J., Drummond, J. T., & Fuqua, C. (2012). The physiology and biochemistry of prokaryotes. Oxford University Press, USA.