Origin of Protein Synthesis

Context:

A new study in Nature has demonstrated that aminoacyl-thiols can link amino acids to RNA without enzymes, providing insights into the origins of protein synthesis on early Earth.

RNA–Protein Puzzle:

Modern cells use ribosomes and enzymes (proteins) to link amino acids to RNA, creating a chicken-and-egg problem in explaining the origins of life.

New Finding:

Researchers discovered that aminoacyl-thiols can attach amino acids to RNA in plain water, without enzymes, under conditions that may have existed on early Earth.

Selectivity:

Despite other reactive molecules being present, aminoacyl-thiols showed strong selectivity for RNA, mirroring processes seen in life today.

Chemical Switch:

Thioesters help amino acids attach to RNA, while their conversion to thioacidsfavours peptide bond formation — separating the two modern steps of protein synthesis.

Prebiotic Chemistry:

Aminoacyl-thiols could have been formed from simple precursors like nitriles and thiols in frozen pools, making this pathway plausible under natural early-Earth conditions.

Significance:

This finding provides a realistic model for how RNA and amino acids may have directly interacted, bridging the gap between the RNA world hypothesis and the origin of protein translation.

RNA

Structure of RNA

Composed of ribose sugar, phosphate group, and four nitrogenous bases: Adenine (A), Guanine (G), Cytosine (C), and Uracil (U) (instead of Thymine).
Mostly single-stranded, though some viruses have double-stranded RNA.
Can fold back on itself to form secondary structures (hairpins, loops, bulges).
Secondary structure formed by base pairing (A–U, C–G).
Tertiary structure results from folding into 3D shapes enabling complex functions.

Types of RNA and Functions

Messenger RNA (mRNA):
- Carries genetic information from DNA to ribosomes.
- Contains codons that code for specific amino acids.
Ribosomal RNA (rRNA):
- Accounts for ~80% of cellular RNA.
- Structural and enzymatic role in ribosomes (site of protein synthesis).
Transfer RNA (tRNA):
- Smallest RNA (~75–95 nucleotides).
- Functions as an adapter molecule, bringing amino acids to ribosomes.
RNA Functions Beyond Protein Synthesis
Gene regulation: microRNAs (miRNA) and small interfering RNAs (siRNA) control expression.
RNA editing & splicing: Small nuclear RNAs (snRNA) involved in modifying transcripts.
Catalytic role: Some RNAs act as ribozymes (catalysts for biochemical reactions).
Genetic material in viruses: Many viruses (e.g., influenza, coronavirus) use RNA as their genome.
Evolutionary Significance
RNA World Hypothesis: RNA was the first genetic material before DNA evolved.
RNA acted as both genetic material and catalyst, driving early life processes.
DNA later replaced RNA as the primary genetic material due to greater stability (double-stranded, repair mechanisms).