Enzymes and Ribozymes
நொதிகள் மற்றும் ரிபோசைம்கள்
Do not assume every biocatalyst is a protein. If you ignore the existence of ribozymes, you lose marks on the most basic classification question in Biomolecules. Biology is defined by its exceptions; learn them.
The idea
Almost all enzymes are proteins with a complex tertiary structure. They accelerate chemical reactions by lowering activation energy at their specific active sites. However, certain nucleic acids, specifically RNA molecules, possess catalytic activity and are termed ribozymes. These molecules challenge the dogma that only proteins can act as biological catalysts.
Why it matters
Biological systems require rapid chemical conversions that would otherwise be too slow to sustain life.
NEET lens
NEET expects you to distinguish between proteinaceous enzymes and ribozymes. Expect 'Statement-based' questions where they claim 'All enzymes are proteins'. Mark this as false. Memorize that ribozymes are RNA, not protein, as this is a high-frequency trap.
Clinical significance
Ribozymes are essential for protein synthesis; the peptidyl transferase activity of the ribosome is performed by rRNA, not protein. If this catalytic function fails, translation stops, leading to immediate cell death. This is the fundamental mechanism of life that antibiotics like chloramphenicol target to kill bacteria.
Introduction
Enzymes are biological catalysts, mostly proteins, that speed up metabolic reactions. Ribozymes are RNA molecules with catalytic activity — 'RNA enzymes'.
Core concept
Enzymes: proteins (apoenzyme = protein part), highly specific (lock and key / induced fit), active site binds substrate. Ribozymes: RNA with catalytic function. Examples: ribozyme splicing introns (self-splicing introns in Tetrahymena, discovered by Cech), peptidyl transferase in ribosome (rRNA, not protein). Evidence for RNA World hypothesis.
Go deeper
Peptidyl transferase reaction (forms peptide bonds during translation) is catalyzed by 23S rRNA (in prokaryotes), not protein. This makes the ribosome a ribozyme.
From Class 10
Enzymes speed up reactions in your body. Most enzymes are proteins. But there's a surprising exception — RNA that acts as enzymes.