eukaryotic

Eukaryotic describes organisms whose cells contain a true nucleus enclosed by a nuclear envelope and a set of membrane-bound organelles. Eukaryotic cells are larger and more structurally complex than prokaryotic cells and possess an internal cytoskeleton and an elaborate endomembrane system.

Most eukaryotes are multicellular, though many unicellular species exist, particularly among the protists. The major lineages include animals, plants, fungi, and diverse protists. The nucleus houses linear chromosomes and is separated from the cytoplasm by the nuclear envelope, with transcription and RNA processing occurring there.

Key organelles include mitochondria for energy production and, in plants and algae, chloroplasts for photosynthesis. The endomembrane system—endoplasmic reticulum, Golgi apparatus, lysosomes, and related vesicles—produces, processes, and sorts proteins and lipids. The cytoskeleton provides shape and motility, and ribosomes in eukaryotic cells are typically 80S, though mitochondria and chloroplasts contain their own 70S ribosomes.

Most eukaryotes reproduce sexually via meiosis and fertilization, although many can reproduce asexually by mitosis. Genome organization is typically multiple linear chromosomes within the nucleus; intron-rich genes are common, and gene expression is regulated by complex nuclear processes.

Evolutionarily, eukaryotes are thought to have arisen from prokaryotic ancestors through endosymbiotic events, with the mitochondrion derived from an ancestral proteobacterium and, in plants and algae, plastids from cyanobacteria. Today, eukaryotes comprise a wide range of life forms, from single-celled protists to large multicellular organisms, occupying nearly every habitat on Earth.