organelli

Organelli, or organelles in English, are specialized structures within cells that carry out defined functions. The term organelle derives from the Latin organellum, meaning a small organ. In eukaryotic cells, well-known organelles include the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, and vacuoles. In plants and algae, chloroplasts enable photosynthesis. Ribosomes, although not surrounded by a membrane, are also essential components involved in protein synthesis.

Organelles can be membrane-bound or non-membrane-bound. Membrane-bound organelles maintain distinct internal environments, enabling separate processes to occur simultaneously, such as transcription in the nucleus and translation in the cytoplasm, or ATP production in mitochondria. Non-membrane-bound components, like ribosomes, perform vital tasks that do not require enclosed compartments. The diversity of organelles reflects their evolutionary origins and cellular needs.

Evolutionarily, mitochondria and chloroplasts are believed to have originated from free-living bacteria that formed endosymbiotic relationships with ancestral eukaryotic cells, a theory supported by their own DNA and ribosomes. Other organelles are thought to have arisen through inward folding of the plasma membrane or through vesicular trafficking and compartmentalization mechanisms.

In prokaryotes, true organelles are less common, though some bacteria possess specialized compartments such as carboxysomes that concentrate certain metabolic reactions. Dysfunction or genetic defects affecting organelles can lead to a range of diseases, including mitochondrial disorders and lysosomal storage diseases.

Organelles are central to cell biology, physiology, and biochemistry, and advances in imaging continue to reveal the dynamic organization and interactions of these cellular units.