Q.11
Which of the following is true of protein synthesis ONLY in prokaryotes?
(A) Translation and transcription are coupled
(B) The codon AUG codes for the start signal
(C) The tRNA anticodon can bind to two or more different codons
(D) The functional ribosomes contain two subunits constructed of proteins and RNA
Answer: (A) Translation and transcription are coupled
Protein synthesis in prokaryotes features coupled transcription and translation, a process absent in eukaryotes due to nuclear separation. This makes option (A) the only statement uniquely true for prokaryotes.
Option Analysis
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(A) Translation and transcription are coupled: In prokaryotes, lacking a nucleus, ribosomes bind nascent mRNA during transcription, enabling simultaneous processes. Eukaryotes separate these in nucleus and cytoplasm.
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(B) The codon AUG codes for the start signal: AUG initiates translation in both prokaryotes (with fMet-tRNA) and eukaryotes, serving as the universal start codon.
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(C) The tRNA anticodon can bind to two or more different codons: Wobble hypothesis allows this degeneracy recognition universally across prokaryotes and eukaryotes.
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(D) The functional ribosomes contain two subunits constructed of proteins and RNA: Both domains feature 70S/80S ribosomes with protein-RNA subunits (30S/50S in prokaryotes; 40S/60S in eukaryotes).
Prokaryotic protein synthesis stands out due to coupled transcription and translation, a key feature for CSIR NET Life Sciences aspirants studying molecular biology. This process allows ribosomes to begin translating mRNA while RNA polymerase still transcribes it, boosting efficiency in bacteria.
Key Prokaryotic Features
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Coupled Processes: No nuclear membrane enables direct mRNA- ribosome interaction post-transcription start.
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Shine-Dalgarno Sequence: Guides 30S subunit to AUG, unlike eukaryotic 5′ cap scanning.
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Polycistronic mRNA: Single transcript encodes multiple proteins via operons.
Why Not Other Options?
AUG start codon, tRNA wobble binding, and ribosomal subunits occur in both cell types, failing “ONLY in prokaryotes” criterion. Coupling defines prokaryotic uniqueness.
CSIR NET Relevance
Questions test these distinctions for exams like CSIR NET, emphasizing efficiency in prokaryotes vs eukaryotic regulation. Master via practice on transcription-translation coupling.
