Overview
Eukaryotes are organisms whose cells possess a true membrane-bound nucleus containing the genetic material and a complex array of membrane-bound organelles. They are distinguished from prokaryotes by their larger cell size, compartmentalised internal structure and linear chromosomes.
Explanation
The domain Eukarya encompasses a vast diversity of organisms, from unicellular yeasts and protozoa to multicellular plants, fungi and animals. In eukaryotic cells the DNA is organised into multiple linear chromosomes housed within a nuclear envelope. The cytoplasm contains membrane-bound organelles such as mitochondria, chloroplasts in algae and plants, endoplasmic reticulum, Golgi apparatus and lysosomes, each performing specialised metabolic functions. Eukaryotic ribosomes are 80S and protein synthesis is compartmentalised between the cytosol and organelles. A dynamic cytoskeleton of microtubules and actin filaments underpins cell shape, motility and intracellular transport. Cell division occurs via mitosis, while meiosis produces haploid gametes in sexually reproducing species; both processes involve a spindle apparatus and ensure orderly chromosome segregation. Introns and extensive regulatory sequences add complexity to gene expression. Endosymbiotic theory posits that mitochondria and chloroplasts originated from symbiotic bacteria; evidence includes their own genomes and bacterial-type ribosomes. Eukaryotes inhabit nearly all environments and engage in ecological roles as producers, consumers and decomposers. Their larger genome sizes and cellular organisation allow for differentiation and the evolution of specialised tissues in multicellular organisms.
Examples and importance
Microbiologically, eukaryotic microorganisms include yeasts such as Saccharomyces cerevisiae, the baker’s yeast used in fermentation; protozoan parasites like Plasmodium falciparum, which causes malaria; Giardia lamblia, an intestinal protozoan; and algae such as diatoms and green algae that contribute to primary production. Fungi encompass both unicellular yeasts and multicellular moulds. Higher plants and animals represent complex multicellular eukaryotes. Understanding eukaryotic cell biology is crucial for fields ranging from medical mycology and parasitology to cell signalling and developmental biology. Many antimicrobial drugs target processes unique to fungi or protozoa while sparing human host cells.
Eukaryotes exhibit remarkable structural and functional diversity rooted in the compartmentalisation of their cells. This organisation enables metabolic specialisation, complex life cycles and the evolution of multicellularity.
Related Terms: Prokaryote, Eukarya, Organelle, Mitochondria, Nucleus