A2.1 Origin of Cells Vocabulary

Vocabulary flashcards covering early Earth conditions, the prebiotic formation of carbon compounds, protocells, the RNA world hypothesis, LUCA, and methods for estimating the origins of life.

Hadean Eon

The period from 4.5 to 4.0 billion years ago on early Earth, characterized by frequent volcanic eruptions, meteorites, lightning, high temperatures, and intense UV radiation.

Reducing Atmosphere

An early Earth atmosphere rich in reactive, electron-donating gases such as ammonia ($NH_3$) and hydrogen ($H_2$), with very little free oxygen ($O_2$).

Inorganic Molecules

Molecules that do not contain both carbon and hydrogen within the same molecule, typically have a small number of atoms, and are associated with non-living matter.

Organic Molecules

Molecules containing both carbon and hydrogen, which can form large structures with many atoms and are usually associated with living organisms.

Oparin-Haldane Hypothesis

An origin-of-life framework proposing four steps: formation of simple organic molecules, assembly into polymers, creation of self-replicating polymers, and packaging into membrane-bound compartments.

Miller-Urey Experiment

A 1953 experiment simulating early Earth conditions that demonstrated simple organic molecules, including amino acids, could form spontaneously from inorganic precursors.

Murchison Meteorite

A 4.6 billion-year-old meteorite found in Australia in 1969 containing organic molecules like amino acids, ribose, and nitrogenous bases, supporting an extraplanetary source of carbon compounds.

Micelles

Spherical structures formed spontaneously by amphipathic fatty acids in water, tucking hydrophobic hydrocarbon tails inward away from the aqueous solvent.

Vesicles

Stable spherical lipid bilayer structures formed from fatty acid micelles under specific concentration and pH conditions, encapsulating fluid and internal chemistry.

Polymerization

An anabolic process in which small subunit molecules (monomers) combine chemically via condensation reactions to form larger chainlike molecules (polymers).

Ribozyme

An RNA molecule capable of functioning as a biological catalyst to speed up chemical reactions, such as RNA cleavage or peptide bond formation in the ribosome.

RNA World Hypothesis

The hypothesis proposing that self-replicating, catalytic RNA molecules existed prior to the evolution of DNA and protein-based life systems.

Last Universal Common Ancestor (LUCA)

The inferred single-celled prokaryotic organism that lived 3.8 to 4.0 billion years ago, from which all modern domains of life (Bacteria, Archaea, and Eukarya) descended.

Stromatolites

Layered sedimentary rock structures formed by mats of photosynthetic cyanobacteria that trap fine sediment, representing some of the earliest fossil evidence of life.

Great Oxygenation Event

A period in Earth's history when early photosynthetic organisms increased atmospheric oxygen concentration from 0% to approximately 20%.

Biomarkers

Molecular fossils, such as ancient lipid compounds encased in sedimentary rocks, that serve as chemical indicators of past living organisms.

Hydrothermal Vents

Seafloor fissures where magma-heated, mineral-rich water reemerges under extreme pressure, providing the hot, anaerobic, chemoautotrophic conditions inferred for LUCA's habitat.

Chemoautotroph

An organism that synthesizes organic compounds from inorganic carbon dioxide and nitrogen using energy derived from chemical reactions (such as with hydrogen gas) rather than sunlight.

Molecular Clock

A method using genomic sequence differences between species to estimate the amount of time elapsed since they diverged from a common ancestor.

Deductive Reasoning

A logical process that uses general premises (such as LUCA's gene traits and metabolic needs) to arrive at a specific conclusion (such as LUCA living near hydrothermal vents).