Periplasm definition: In Gram-negative bacteria, what does the term “periplasm” specifically refer to?
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Athe area between the inner and outer membranes of gram-negative bacteria
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Bthe area between the inner and outer membranes of Gram-positive bacteria
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Cthe interior portion of mitochondria
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Dthe area outside the cell membrane that is influenced by the polymers
Answer
Correct Answer: the area between the inner and outer membranes of gram-negative bacteria
Explanation
Introduction / Context:Periplasm is a compartment unique to Gram-negative bacteria (and some diderm bacteria). Its correct definition is essential to understand nutrient uptake, envelope biochemistry, and antibiotic access.
Given Data / Assumptions:
- Gram-negative envelopes include: inner (cytoplasmic) membrane, thin peptidoglycan, and an outer membrane.
- Periplasm contains enzymes, binding proteins, peptidoglycan, and transport intermediates.
- Gram-positive bacteria do not possess an outer membrane.
Concept / Approach:The periplasm is the aqueous space between the inner and outer membranes in Gram-negative bacteria, including the thin peptidoglycan layer and periplasmic proteins. By contrast, Gram-positives lack this defined periplasmic compartment due to the absence of an outer membrane.
Step-by-Step Solution:
Identify structural requirement: outer membrane present → Gram-negative.Define periplasm: compartment between membranes, not outside the cell entirely.Select the option specifying Gram-negative periplasm.Verification / Alternative check:Biochemical fractionation yields a distinct periplasmic fraction in Gram-negatives rich in periplasmic binding proteins and enzymes (e.g., beta-lactamases).
Why Other Options Are Wrong:Gram-positive periplasm (B): Lacks an outer membrane, so no true periplasmic space. Mitochondria (C): Eukaryotic organelles, unrelated. Outside the membrane (D): Refers to external milieu/ECM, not periplasm.
Common Pitfalls:Equating “space near the membrane” with periplasm; periplasm is a defined compartment bounded by two membranes in Gram-negative cells.
Final Answer:the area between the inner and outer membranes of gram-negative bacteria