new_n_lost
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Which of the following structures is found only in Gram-negative microorganisms?
A. Cell envelope
B. Exotoxin
C. Peptidoglycan
D. Periplasmic space
E. Teichoic acids
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| Feyza
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D. periplasmic space...
bc only the gr (-) s have an outer name and the pp space is the space between the inner and the outer so only they have it...
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O my Lord! Open my chest for me ( grant me self-confidence ) and ease my task for me.Ta-Ha 25-26.
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| mytime
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YO D.
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| sss sss
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D
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| GoodGirl
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DDDDDDDDDDDDDD
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| new_n_lost
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The correct answer is D.
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 transport of various nutrients, and peptidoglycan, as well as a portion of the lipoprotein that firmly anchors the outer membrane to the peptidoglycan. Gram-positives do not have outer membranes.
Choice A, 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.
Choice B, 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.
Choice C, 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.
Choice E, teichoic acids, are found exclusively in gram-positive organisms.
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FORUM RULES-- Those who believe in telekinesis, raise my hand. I get enough exercise just by pushing my luck --P4U World.." The pure and simple truth is rarely pure and never simple."
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| new_n_lost
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FORUM RULES-- Those who believe in telekinesis, raise my hand. I get enough exercise just by pushing my luck --P4U World.." The pure and simple truth is rarely pure and never simple."
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| lq2006
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D
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| SmokyWaters
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nice explanation nnl....
btw... you must not be that NEW anymore? :P
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| SmokyWaters
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| drduck
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| mojnia
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