Step 1: Understanding the Concept:
The traditional biological paradigm, often referred to as the "One Gene-One Enzyme" hypothesis, initially suggested that all biological catalysts are proteins. However, the discovery of ribozymes in the early 1980s by Thomas Cech and Sidney Altman (who were awarded the Nobel Prize for this discovery) fundamentally changed our understanding of molecular biology. A ribozyme is defined as a ribonucleic acid (RNA) molecule that possesses the ability to catalyze specific biochemical reactions, much like a protein enzyme. This discovery lent significant weight to the "RNA World Hypothesis," which proposes that early life forms relied on RNA both for genetic information storage and for metabolic catalysis before the evolution of DNA and proteins.
Step 2: Detailed Explanation:
In the process of protein synthesis, which occurs within the ribosome, amino acids are linked together by peptide bonds. For decades, it was debated whether the protein components or the RNA components of the ribosome were responsible for this crucial catalytic step. We now know that the ribosome is, in fact, a ribozyme.
In prokaryotic organisms, such as {Escherichia coli}, the ribosome consists of a small 30S subunit and a large 50S subunit. The 50S large subunit contains two main RNA molecules: the 23S rRNA and the 5S rRNA. Research has demonstrated that the 23S rRNA is the actual catalyst responsible for "Peptidyl Transferase Activity." This means it facilitates the formation of the peptide bond between the amino acid in the P-site and the amino acid in the A-site of the ribosome.
While the other options represent ribosomal RNA, they do not serve as the primary ribozyme in the context of the peptidyl transferase center as commonly defined in standard biological curricula:
- (B) 28S rRNA is found in the large subunit (60S) of eukaryotes. While it also has catalytic activity, 23S is the classic prokaryotic example.
- (C) 18S rRNA is a component of the small subunit (40S) in eukaryotes and is primarily involved in mRNA alignment and binding.
- (D) 5.8S rRNA is also eukaryotic and contributes to the structural integrity of the large subunit.
Step 4: Final Answer:
The 23S rRNA molecule, found in the large ribosomal subunit of prokaryotes, acts as a biological catalyst for peptide bond formation. Because it is an RNA molecule with enzymatic properties, it is a ribozyme.
Therefore, the correct option is (A).