Which of the following structures is found only in Gram-negative microorganisms?
This question requires you to appreciate the key structural difference between gram-positive and gram-negative microorganisms. Most gram-negatives (other than exceptional microorganisms, such as Mycoplasma, that lack a cell wall) have a more complex cell envelope than gram-positive microorganisms. It includes both a cytoplasmic membrane as well as an outer membrane. Between these two membranes is the periplasmic space, which contains enzymes such as phosphatase and penicillinase, binding proteins for the transpo of various nutrients, and peptidoglycan, as well as a poion of the lipoprotein that firmly anchors the outer that a baby can form with an acute membrane to the peptidoglycan. Gram-positives do not have outer membranes. The cell envelope is incorrect because both gram-positive and gram-negative microorganisms have this structure, which is defined as all the layers that enclose the cytosol of the bacterium. It is the composition of the envelope that differs between gram-positives and gram-negatives. Exotoxin is not exclusive to gram-negative microorganisms, but is also found in some gram-positives. By contrast, endotoxin (lipopolysaccharide; LPS) is found exclusively in gram- negatives. Peptidoglycan is found in the cell walls of both gram-positive and gram-negative microorganisms. Note that there is a larger amount of peptidoglycan in gram-positive microorganisms. Ref: Brooks G.F. (2013). Chapter 2. Cell Structure. In G.F. Brooks (Ed), Jawetz, Melnick, & Adelberg's Medical Microbiology, 26e.
Cell envelope
Exotoxin
Peptidoglycan
Periplasmic space