Origin of life: self-replication and homochirality

7 problems

• Prebiotic transfer of chiral bias from sugars to amino acids

  Partially resolved

  Life pairs right-handed sugars with left-handed amino acids, and RNA made of right-handed sugars is known to prefer attaching left-handed amino acids. Whether this preference was strong enough under early-Earth conditions to pass one chiral bias on to the other molecule family is open.

• Escape from Eigen's paradox for prebiotic genomes

  Partially resolved

  Copying without enzymes is sloppy, so only short sequences survive copying errors, yet an accurate copying enzyme needs a sequence long enough to encode it. A 2026 RNA enzyme only 45 letters long narrowed this gap, and which mechanism kept genetic information intact over many generations is still open.

• How chemistry produced the first evolving replicator

  Open

  Somewhere between simple molecules and the first cell, a chemical system began copying itself with variations that natural selection could act on. Which physical and chemical steps achieved this is unknown.

• Why the standard genetic code has its particular structure

  Contested

  All life reads three-letter DNA words with nearly the same dictionary, which assigns 64 words to 20 amino acids. That dictionary limits the damage from copying errors better than almost any random dictionary, and whether this came from chemistry, history or selection is unknown.

• How life came to use only one molecular handedness

  Contested

  Many biological molecules come in mirror-image forms, yet life uses only left-handed amino acids and right-handed sugars. Whether this choice was set by a physical bias or by chance, and how it was amplified to purity, is unknown.

• Sustained exponential self-replication by a polymerase ribozyme

  Partially resolved

  In the RNA-world idea, early life used RNA both as genes and as enzymes, which requires an RNA able to copy itself. In 2026 a 45-nucleotide RNA enzyme copied itself and its partner strand, but too slowly and too inaccurately for its numbers to keep growing over many rounds.

• Separating copied RNA strands for repeated nonenzymatic copying

  Open

  When RNA is copied without enzymes, the copy sticks tightly to its template, and the heat that pulls them apart also lets them snap back before the next copy is made. A physical cycle that separates and recopies strands is needed.