Passage:
For decades following the elucidation of the double-helical structure of DNA, molecular biology operated under the central premise that cellular catalysis was the exclusive domain of proteins. Enzymes, composed of complex three-dimensional arrangements of amino acids, were considered uniquely capable of lowering activation energies to mediate biochemical reactions, while nucleic acids—DNA and RNA—were viewed strictly as passive repositories and conveyors of genetic information. This paradigm was fundamentally challenged in the early 1980s through independent investigations conducted by Thomas Cech and Sidney Altman. Investigating the processing of precursor ribosomal RNA (pre-rRNA) in the ciliated protozoan Tetrahymena thermophila, Cech observed that a 413-nucleotide intervening sequence, or intron, excised itself from the 26S rRNA precursor in vitro even in the total absence of protein enzymes, requiring only guanosine nucleotides and divalent cations such as magnesium. Concurrently, Altman established that the catalytic core of ribonuclease P, an enzyme responsible for processing transfer RNA precursors in Escherichia coli, resided within its ribonucleic acid subunit (M1 RNA) rather than its protein component. These findings demonstrated that RNA could act as an enzyme—a catalytic molecule termed a 'ribozyme'—thereby providing vital empirical support for the 'RNA world' hypothesis, which posits that early evolutionary life forms utilized RNA for both enzymatic catalysis and genetic storage.
Statement:
According to the passage, Thomas Cech's in vitro experiments demonstrated that the self-splicing 413-nucleotide intron from Tetrahymena thermophila pre-rRNA required guanosine nucleotides and divalent cations to excise itself, but functioned in the total absence of protein enzymes.
Cevap: Cevap