What is a gram negative peptidoglycan like?

• A. Very thick
• B. Absent
• C. Very thin
• D. Moderately thick

Answer: (C)

The main idea here is the thickness of the peptidoglycan layer in Gram-negative bacteria. They have a very thin peptidoglycan layer, situated in the periplasmic space between the inner cytoplasmic membrane and the outer membrane that contains lipopolysaccharides. This thin layer contrasts with Gram-positive bacteria, which have a much thicker peptidoglycan wall. Because the peptidoglycan is so thin, the crystal violet stain is washed out more easily during Gram staining, and the cells take up the counterstain, appearing pink. So describing the peptidoglycan as very thin accurately reflects the structure of Gram-negative bacteria. The other descriptions don’t fit: a very thick layer is characteristic of Gram-positive bacteria, an absent wall would be incorrect since Gram-negative cells do have peptidoglycan, and a moderately thick description isn’t the standard portrayal for Gram-negative organisms.