The Ribosome and Protein Translation
The ribosome is the molecular machine on which messenger RNA is translated into protein. It coordinates messenger RNA and transfer RNAs while catalyzing formation of the growing polypeptide chain.
The Investigative Question
How does the cell convert a sequence of messenger-RNA codons into an ordered chain of amino acids?
What We Observe
Protein synthesis occurs on ribosomes.
The ribosome binds messenger RNA, receives charged transfer RNAs, checks codon-anticodon interactions, and positions amino acids so that they can be joined into a growing polypeptide chain.
As the ribosome moves along the messenger RNA, the order of codons determines the order in which amino acids are incorporated.
Scientific Background
Ribosomes consist of ribosomal RNA and proteins arranged into large and small subunits.
The small subunit plays an important role in decoding messenger RNA. The large subunit contains the peptidyl-transferase center responsible for peptide-bond formation.
Structural studies have shown that ribosomal RNA occupies the catalytic core of the ribosome. The ribosome is therefore a ribozyme as well as a large ribonucleoprotein machine.
Why It Matters
The ribosome brings several components of biological information processing together in one system.
Messenger RNA provides the sequence to be read. Charged tRNAs connect codons with amino acids. The ribosome maintains the reading frame, selects appropriate tRNAs, and catalyzes assembly of the protein.
The resulting amino-acid sequence can then fold into a protein whose properties depend upon that sequence.
What Is Known
The major structural and mechanistic features of translation are known in considerable detail.
Ribosomal RNA forms much of the structural and catalytic core. Translation factors assist initiation, elongation, termination, and quality control.
Codon recognition and peptide synthesis occur repeatedly as the ribosome proceeds along messenger RNA.
What Is Proposed
The RNA-rich catalytic core of the ribosome is often interpreted as evidence of an evolutionary history extending back toward an RNA-dominated stage of early life.
Origin models propose that simpler RNA-based peptide-synthesis systems preceded the modern ribosome and gradually acquired proteins and increasingly sophisticated functions.
What Remains Uncertain
The modern ribosome is highly complex, and its ancient evolutionary history cannot be observed directly.
Researchers continue to reconstruct possible ancestral ribosomes and investigate how primitive RNA-peptide interactions could have developed into processive coded protein synthesis.
Key Numbers
Messenger RNA is read three nucleotides at a time. Standard translation uses 61 amino-acid codons to specify 20 principal amino acids.
Design Relevance
The ribosome is relevant to Intelligent Design because it is a highly coordinated molecular system that converts encoded nucleotide sequences into ordered proteins.
Its operation depends upon multiple interacting components, energy-consuming steps, molecular recognition, and quality control.
At the same time, the RNA-based catalytic core provides important evidence considered by natural evolutionary models. A responsible design investigation must examine both the remarkable organization of the modern ribosome and proposed pathways to simpler ancestral forms.
Assessment
The ribosome demonstrates that biological information is not merely stored. It is processed through physical machinery capable of converting one kind of molecular sequence into another.
The operation of that machinery is well understood in modern organisms. Its origin and early evolution remain important questions.