Prokaryotic cell traits: identify the statement that is NOT true Which of the following statements does NOT correctly describe prokaryotic organisms (bacteria or archaea)?
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AThe nucleus is not bounded by a nuclear membrane.
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BChromosomes do not contain histones as major packaging proteins.
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C80S ribosomes are distributed in the cytoplasm.
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DThe cell wall contains peptidoglycan as a major component in bacteria.
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EGenetic material is typically a single circular chromosome.
Answer
Correct Answer: 80S ribosomes are distributed in the cytoplasm.
Explanation
Introduction / Context:Prokaryotes exhibit hallmark differences from eukaryotes in cellular organization, genome structure, and protein synthesis machinery. Identifying false statements about prokaryotes is a common test of foundational microbiology knowledge. The ribosome size is a particularly important discriminator in pharmacology and diagnostics.
Given Data / Assumptions:
- Prokaryotes lack a true nucleus and membrane-bound organelles.
- Bacterial cell walls contain peptidoglycan; archaeal walls lack peptidoglycan.
- Ribosome sedimentation coefficients differ between prokaryotes and eukaryotes.
Concept / Approach:
Prokaryotic ribosomes are 70S, composed of 50S and 30S subunits. Eukaryotic cytosolic ribosomes are 80S (60S + 40S). Therefore, any statement placing 80S ribosomes in the prokaryotic cytoplasm is false. Other statements align with standard descriptions: absence of a nuclear membrane, limited or absent histones in bacteria (some archaea possess histone-like proteins), and peptidoglycan in bacterial cell walls.
Step-by-Step Solution:
Check ribosome size: prokaryote = 70S; eukaryote cytosol = 80S.Verify nucleus: prokaryotes have a nucleoid, not a membrane-bound nucleus.Confirm bacterial cell wall: peptidoglycan is a defining feature of bacteria.Conclude that the 80S ribosome statement is the incorrect one.Verification / Alternative check:
Antibiotics such as tetracyclines target 30S subunits, exploiting the 70S ribosome difference to achieve selective toxicity against bacteria.
Why Other Options Are Wrong (i.e., they are true):
- No nuclear membrane: true for prokaryotes.
- Chromosomes without canonical eukaryotic histones: true for bacteria; some archaea have histone-like proteins, but overall the statement holds as written.
- Peptidoglycan in bacterial walls: true, though absent in archaea.
- Single circular chromosome: typical of bacteria, with exceptions.
Common Pitfalls:
- Confusing 70S vs 80S, especially when considering mitochondrial/chloroplast 70S ribosomes inside eukaryotes.
- Assuming all prokaryotes share identical wall chemistry; archaea are different.
Final Answer:
80S ribosomes are distributed in the cytoplasm.