A2.1-Origin-of-Cells

Cell

The fundamental structural and functional unit of life; the smallest entity capable of independent metabolism, reproduction, and maintaining homeostasis.

Cell Theory

States that: (1) all living organisms are composed of one or more cells, (2) the cell is the basic unit of structure and function in living things, and (3) all cells arise from pre-existing cells through division.

DNA (Deoxyribonucleic Acid)

The molecule that stores hereditary information in nearly all living organisms; composed of nucleotide sequences encoding genetic instructions for protein synthesis.

RNA (Ribonucleic Acid)

A versatile molecule that carries genetic information from DNA (mRNA), catalyzes reactions (ribozyme), and plays roles in protein synthesis; thought to have come before DNA in early life forms.

Enzyme

The state of Earth before the emergence of life (~4 billion years ago), with a reducing atmosphere (rich in CH₄, NH₃, H₂, and H₂O vapor) and high volcanic and electrical activity and UV.

Hydrothermal Vents

Submarine fissures emitting hot, mineral-rich water. They may have provided ideal conditions (energy gradients and catalytic surfaces) for the synthesis of organic molecules and the origin of life.

Thermophiles

Heat-loving microorganisms that thrive in extreme temperatures near hydrothermal vents; their existence supports the theory that life originated in such environments.

Stromatolite

Layered rock structures formed by colonies of cyanobacteria trapping sediment; represent some of the earliest fossil evidence of life (~3.5 billion years old).

LUCA (Last Universal Common Ancestor)

The most recent common ancestor from which all currently living organisms descended; likely a simple, cell-like organism with RNA/DNA and a cell membrane.

Miller-Urey Experiment

1953 experiment simulating early Earth’s atmosphere with gases (CH₄, NH₃, H₂, H₂O) and electrical sparks; produced amino acids and other organic molecules, supporting abiogenesis theories.

Pre-biotic Organic Compounds

Naturally formed carbon-based molecules (amino acids, sugars, nucleotides) that arose before life, possibly through lightning, volcanic activity, or hydrothermal processes.

Vesicles

Small, membrane-bound droplets formed spontaneously by phospholipids in water; may have served as primitive cell models capable of enclosing molecules.

Phospholipid

Amphipathic molecule with hydrophilic heads and hydrophobic tails that self-assemble into bilayers in water, forming the structural basis of biological membranes.

Amphipathic

Having both hydrophilic (water-attracting) and hydrophobic (water-repelling) parts; characteristic of membrane lipids.

Hydrophilic

Molecules or regions that are attracted to and interact well with water (polar or charged).

Hydrophobic

Molecules or regions that repel water (non-polar); they cluster together to minimize contact with water.

Genetic Code

The nearly universal system of 64 codons (triplets of RNA nucleotides) that specify amino acids for protein synthesis; evidence of common ancestry among all life forms.

RNA World Hypothesis

The theory that early life was based on self-replicating RNA molecules that both stored genetic information and catalyzed chemical reactions before DNA and proteins evolved.

Ribozyme

RNA molecule capable of catalyzing specific biochemical reactions, such as self-splicing or RNA replication; supports the RNA World hypothesis.

Self-Replication

The ability of molecules, especially nucleic acids like RNA, to make exact copies of themselves, enabling inheritance and evolution.

Oxygenation of the Atmosphere

The rise of atmospheric oxygen due to photosynthetic cyanobacteria during the Great Oxygenation Event (~2.4 billion years ago), enabling aerobic respiration and forming the ozone layer.

Convergent Evolution

Independent evolution of similar traits in species not closely related, often due to similar environmental pressures (e.g., wings in bats and birds).

Banded Iron Rock (BIF)

Sedimentary rock with alternating iron oxide layers, formed when oxygen produced by early photosynthetic organisms reacted with dissolved iron in oceans.

Zircon Particles

Tiny mineral fragments dating back over 4 billion years; isotopic ratios suggest the presence of liquid water and potentially early biological activity.

Spontaneous Generation

The disproven hypothesis that living organisms could arise directly from nonliving matter; replaced by biogenesis and abiogenesis theories.

Domains

The highest taxonomic rank classifying all life into three groups: Eubacteria (Bacteria), Archaea, and Eukarya.

Eubacteria (Bacteria)

Domain of prokaryotic, unicellular organisms with peptidoglycan cell walls and simple cellular organization; includes most common bacteria.

Archaea

Domain of prokaryotes distinct from bacteria; often extremophiles (living in harsh environments) with unique RNA sequences and membrane lipids.

Eukarya

Domain of organisms composed of eukaryotic cells, characterized by membrane-bound organelles and nuclei (includes animals, plants, fungi, protists).

Evolution

The change in heritable traits of biological populations over successive generations due to natural selection, mutation, gene flow, and genetic drift.