Molecules in the UniverseFrom Helium Hydride to Amino Acids

Real basis

• Helium hydride ion (HeH⁺): the first molecule to form in the universe. It was only detected for the first time in 2019, in a planetary nebula.

• Molecular hydrogen (H₂): the most abundant molecule in the universe. Before the first stars were born, gas needed it to radiate heat away so it could collapse.

• Hydroxyl (OH): in 1963, the first molecule detected in interstellar space by radio telescopes.

• Carbon monoxide (CO): the second most abundant molecule in molecular clouds; radio astronomers use it to map the invisible clouds of molecular hydrogen.

• Water (H₂O): abundant in interstellar ice grains, comets and planetary disks. Some of Earth's water may have come from asteroids.

• Ammonia (NH₃): detected in 1968, the first polyatomic molecule found in interstellar space.

• Methane (CH₄): Titan has lakes and rain made of methane.

• Silicate dust (SiO₄): the main component of interstellar dust, which later clumped into rocky planets.

• Hydrogen cyanide (HCN): highly toxic, yet possibly a key raw material for making nucleobases and amino acids when life began.

• Formaldehyde (H₂CO): the first interstellar organic polyatomic molecule, detected in 1969.

• Polycyclic aromatic hydrocarbons (PAH): among the most common large molecules in interstellar space, thought to lock up a good share of the cosmos's carbon.

• Fullerenes (C₆₀): found in a planetary nebula in 2010, and among the largest interstellar molecules known.

• Glycolaldehyde (C₂H₄O₂): one of the simplest sugar molecules, found in a gas cloud near the center of the Milky Way.

• Olivine ((Mg,Fe)₂SiO₄): the main mineral of the upper mantle; its crystals are also found in comet dust.

• Pyroxene ((Mg,Ca)SiO₃): a common mineral in basalt and lunar rocks.

• Magnetite (Fe₃O₄): the most strongly magnetic natural mineral; some bacteria and migratory birds also carry microcrystals of it.

• Quartz (SiO₂): the signature mineral of continental crust and the main component of sand.

• Feldspar (KAlSi₃O₈): the most abundant mineral group in the Earth's crust.

• Zircon (ZrSiO₄): extremely durable. Zircons from Australia show that liquid water may already have existed on Earth 4.4 billion years ago.

• Diamond (C): carbon atoms packed tightly in a tetrahedral pattern, the hardest natural substance. Some meteorites hide nanodiamonds older than the solar system.

• Clay minerals (Al₂Si₂O₅(OH)₄): clay surfaces may have helped early RNA fragments line up and link together.

• Calcite (CaCO₃): a component of limestone and many shells; trilobite eyes were calcite crystals.

• Apatite (Ca₅(PO₄)₃): the main inorganic component of tooth enamel and bone.

• Pyrite (FeS₂): nicknamed "fool's gold". One hypothesis for the origin of life holds that the first metabolic reactions took place on iron sulfide surfaces.

• Glycine (C₂H₅NO₂): the simplest amino acid; Rosetta also detected it on comet 67P.

• Adenine (C₅H₅N₅): one of the nucleobases of DNA and RNA; it can be assembled from 5 hydrogen cyanide molecules.

• Ribose (C₅H₁₀O₅): the sugar backbone of RNA; it can form when formaldehyde polymerizes on mineral surfaces.

• Nucleotides (NMP): the basic unit of nucleic acids: a base, a ribose and a phosphate joined together.

• Fatty acids (RCOOH): placed in water, they spontaneously form double-layered vesicles, which may have been the first cell membranes.

• RNA: a molecule that can both store information and catalyze reactions, the star of the RNA world hypothesis.

• ATP: the cell's energy currency. The total ATP a human body makes and breaks down each day is close to its own body weight.

• DNA: a genetic molecule more stable than RNA; all living cellular organisms use it to store their genes.

• Chlorophyll (C₅₅H₇₂MgN₄O₅): absorbs red and blue light and reflects green, with a single magnesium atom at its center.

• Hemoglobin (Hb): carries oxygen on iron atoms, which is what makes blood red.

• Formamide (HCONH₂): heating formamide over mineral catalysts can yield all four nucleobases and precursors of many amino acids at once.

• Urea (CO(NH₂)₂): in 1828 Wöhler synthesized urea from inorganic matter, the first proof that organic compounds need not come from living things.

• Alanine (Ala): one of the amino acids with the highest yield in the 1953 Miller–Urey experiment; it is also found in the Murchison meteorite.

• Aspartic acid (Asp): found in both the Miller–Urey experiment and meteorites; it is also the starting point for making many other amino acids.

• Serine (Ser): its name comes from silk (Latin "sericum"); it was first isolated from sericin, a silk protein.

• Glutamic acid (Glu): the main component of MSG is sodium glutamate, which gives food its "umami" taste.

• Valine (Val): sickle-cell anemia is caused by one glutamic acid in hemoglobin being replaced by valine.

• Guanine (G): first isolated from bird droppings (guano), which is where its name comes from.

• Cytosine (C): forms three hydrogen bonds with guanine, the strongest of the base pairs.

• Uracil (U): a base unique to RNA. Cytosine becomes uracil when it loses an amino group; uracil has also been detected in the Murchison meteorite.

• Leucine (Leu): one of the most common amino acids in proteins; the human body cannot make it.

• Isoleucine (Ile): has exactly the same atoms as leucine, arranged differently; the two are isomers.

• Proline (Pro): its side chain loops back to join the main chain, acting like a "kink" in the protein chain; collagen is especially rich in it.

• Threonine (Thr): not discovered until 1935, the last of the 20 standard amino acids to be found.

• Homochirality (L / D): life uses only left-handed amino acids and right-handed sugars. The Murchison meteorite has slightly more left-handed amino acids, hinting that this preference may have come from space.

• Phospholipids (PL): one end loves water and the other repels it, so they line up into double layers by themselves. Every cell membrane today is made of them.

• Iron–sulfur clusters (Fe–S): among the oldest protein cofactors; their structure closely resembles the iron sulfide minerals of hot springs, supporting the hypothesis that life began at deep-sea hydrothermal vents.

• Ribozyme (RNA*): RNA with catalytic ability. Cech and Altman won the 1989 Nobel Prize in Chemistry for discovering it.

• Peptide (Gly-Ala): a short chain of amino acids joined by losing water. Repeated wetting and drying beside a hot spring pool can link amino acids together on their own.

• tRNA: a small clover-shaped RNA that recognizes a codon at one end and carries an amino acid at the other, the "translator" of the genetic code.

• NAD⁺: a coenzyme that carries electrons, with a complete nucleotide in the molecule; it may be a relic of the RNA world.

• Coenzyme A (CoA): a central hub of metabolism, needed by both fatty acid metabolism and the citric acid cycle.

• Cysteine (Cys): a sulfur-containing amino acid; two cysteines can form a disulfide bond. Perming hair means breaking and re-forming these bonds.

• Methionine (Met): the first amino acid of almost every protein; it is what the start codon AUG codes for.

• Histidine (His): a common "carrier" in enzyme active sites, able to accept and give up protons.

• Lysine (Lys): an essential amino acid that is scarce in cereal grains, so living on grains alone easily leads to a deficiency.

• Arginine (Arg): the body uses it to make nitric oxide, which helps blood vessels relax.

• Asparagine (Asn): isolated from asparagus juice in 1806, the first amino acid ever discovered.

• Glutamine (Gln): the most abundant amino acid in the blood, supplying energy to immune cells and gut cells.

• Ribosome (rRNA): the molecular machine that translates messenger RNA into protein. The catalyst is RNA, not protein, so it is seen as a living fossil of the RNA world.

• Genetic code (64 → 20): 64 three-letter codons stand for 20 amino acids plus stop signals, and almost all organisms share the same code.

• Protein: predicting a protein's structure from its sequence was a problem for half a century, and in 2020 AlphaFold essentially solved it.

• Phenylalanine (Phe): in 1961 Nirenberg used RNA containing only U to synthesize a string of phenylalanine, cracking the first codon, UUU.

• Tyrosine (Tyr): first isolated from cheese, and its name comes from the Greek word for "cheese".

• Tryptophan (Trp): the largest of the standard amino acids; the body uses it to make serotonin and melatonin.

• Thymine (T): uracil plus a methyl group. DNA uses it in place of uracil, which makes errors from cytosine deamination easier to spot and repair.

• Deoxyribose (C₅H₁₀O₄): has one oxygen atom fewer than ribose, which makes DNA much more stable than RNA.

• Enzymes (E): biological catalysts. Some reactions would take tens of millions of years without an enzyme and only milliseconds with one.

• Glucose (C₆H₁₂O₆): the product of photosynthesis. The human brain uses about 120 g of glucose a day.

• Cellulose ((C₆H₁₀O₅)ₙ): the most abundant organic compound on Earth, built from chained glucose. Cattle and sheep need microbes in their stomachs to digest it.

• Collagen (Col): the most abundant protein in animals, gluing cells into tissue. The rise of multicellular animals may not have been possible without it.

• Chitin ((C₈H₁₃NO₅)ₙ): the main component of arthropod exoskeletons and fungal cell walls, the second most abundant polysaccharide in nature.

• Lignin: makes plant stems rigid so they can grow tall. The huge coal deposits of the Carboniferous may be related to fungi of the time not yet being good at breaking it down.

Related research

These studies relate to this topic but are not direct proof of this page.

• The Miller–Urey experiment: A graduate student sealed water, methane, ammonia and hydrogen in a flask and kept sparking it, and got the amino acids that make up proteins.

  Source: Miller, Science 1953, "A production of amino acids under possible primitive earth conditions"

• Nucleotides without enzymes: Found a more “natural” chemical route to directly make RNA components under primitive conditions.

  Source: Powner, Gerland & Sutherland, Nature 2009, "Synthesis of activated pyrimidine ribonucleotides in prebiotically plausible conditions"

• Amino acids in space: Amino acids of non-terrestrial origin were found in the Murchison meteorite. The raw materials of life may be common in the universe.

  Source: Kvenvolden et al., Nature 1970, "Evidence for extraterrestrial amino-acids and hydrocarbons in the Murchison meteorite"

• Deep-sea hot springs: Ecosystems that do not depend on sunlight exist around deep-sea hot springs, giving the origin of life a new candidate site.

  Source: Corliss et al., Science 1979, "Submarine thermal springs on the Galápagos Rift"