Q.33 Carl Woese used the gene sequence of which one of the following for phylogenetic
taxonomy of prokaryotes?
(A) A ribosomal RNA of large ribosomal subunit
(B) A ribosomal RNA of small ribosomal subunit
(C) A ribosomal protein of large ribosomal subunit
(D) A ribosomal protein of small ribosomal subunit
Carl Woese’s groundbreaking work revolutionized prokaryotic classification by using 16S ribosomal RNA sequences. This approach enabled the discovery of Archaea as a distinct domain. The correct answer to the question is option (B).
Question Breakdown
The query tests knowledge of Carl Woese’s method for phylogenetic taxonomy of prokaryotes, specifically which ribosomal component he sequenced.
Option Analysis
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(A) A ribosomal RNA of large ribosomal subunit: Incorrect. The large subunit rRNA (23S in prokaryotes) was not Woese’s primary tool; he focused on the small subunit for its conserved yet variable sequence ideal for deep phylogeny.
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(B) A ribosomal RNA of small ribosomal subunit: Correct. Woese used 16S rRNA (small subunit) sequences, starting from oligonucleotide catalogs, to build trees distinguishing Bacteria and Archaea due to its universal presence and evolutionary signal.
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(C) A ribosomal protein of large ribosomal subunit: Incorrect. Ribosomal proteins vary more and lack the structural conservation of rRNA, making them unsuitable for Woese’s broad taxonomic work.
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(D) A ribosomal protein of small ribosomal subunit: Incorrect. While small subunit proteins exist, Woese prioritized rRNA over proteins for its functional constancy across life.
Introduction: Unlocking Prokaryotic Evolution with Carl Woese 16S Ribosomal RNA
Carl Woese transformed biology by employing 16S ribosomal RNA (small ribosomal subunit) sequences for phylogenetic taxonomy of prokaryotes, revealing Archaea as the third domain of life. This Carl Woese ribosomal RNA method outperformed traditional traits, offering precise evolutionary trees via conserved gene sequences. Perfect for students tackling competitive exams like IIT JAM Biotechnology.
Why 16S Ribosomal RNA Excelled in Prokaryote Classification
Woese selected 16S rRNA for its ~1500 nucleotides balancing conservation (universal function in translation) and variation (species-specific markers). Early work involved 5S rRNA (also small subunit-related), but small ribosomal subunit rRNA proved superior for resolving deep branches in Bacteria and Archaea. Large subunit options like 23S rRNA were too variable for ancient divergences.
Evaluating Ribosomal Proteins vs RNA in Woese’s Framework
Ribosomal proteins from large or small subunits were dismissed; proteins evolve faster and lack rRNA’s secondary structure stability for homology detection. Woese’s oligonucleotide catalogs from 16S rRNA enabled quantitative phylogeny, unlike protein ambiguity.
Impact on Modern Microbiology and Exam Prep
Today, 16S ribosomal RNA sequencing remains the gold standard for microbial identification in metagenomics. For IIT JAM aspirants, master this: Woese’s choice of small subunit rRNA over large subunit or proteins underscores molecular evolution principles. Practice similar MCQs to ace prokaryotic taxonomy sections.
