ultrastructure

Ultrastructure refers to the fine, subcellular architecture of cells and tissues as revealed by electron microscopy. It encompasses the organization of organelles, membranes, macromolecular complexes, and cytoskeletal elements that lie below the resolution of light microscopy.

Electron microscopy methods, including transmission electron microscopy (TEM) for internal organization and scanning electron microscopy (SEM) for surface topology, enable ultrastructural studies. Advances such as cryo-electron microscopy and cryo-electron tomography permit imaging near-native states and three-dimensional reconstructions. Specimen preparation typically involves chemical fixation (glutaraldehyde), postfixation with osmium tetroxide, dehydration, embedding in resin, ultrathin sectioning, and contrasting with heavy metals to enhance contrast.

Ultrastructural analysis reveals details such as mitochondrial cristae, endoplasmic reticulum networks, Golgi cisternae, vesicular transport carriers, lysosomes, peroxisomes, and nuclear envelope organization, as well as synaptic vesicles and cytoskeletal filaments. In plants and algae, thylakoid membranes and chloroplast organization are studied.

While ultrastructure provides crucial insights into function and pathology, it is subject to preparation artifacts and may not reflect native states. Light microscopy lacks the resolution to resolve many ultrastructural features, and interpretation requires expertise in EM techniques and image analysis. Recent developments including cryo-EM and tomography have extended capability toward near-native and three-dimensional representations.

Historically, the concept emerged with the advent of electron microscopy in the 1930s–1950s, with key contributions by Keith Porter and others who introduced the study of cellular ultrastructure.