jádry

Jádry is the Czech plural form of jádro, meaning nucleus or core. In physics and chemistry, the nucleus is the central part of an atom, composed of protons and neutrons, collectively called nucleons. It contains nearly all the atom’s mass and carries a positive charge equal to the number of protons (the atomic number). Nuclei are about 1e-14 meters across. Nucleons are bound by the strong nuclear force; the binding energy determines stability and radioactive decay. Isotopes differ in their number of neutrons. Nuclear reactions include fusion, where light nuclei combine; fission, where heavy nuclei split. Unstable nuclei decay, emitting radiation such as alpha, beta, and gamma particles. Examples include the hydrogen-1 nucleus (a single proton), carbon-12, and uranium-235.

In biology, jádro denotes the organelle in eukaryotic cells that contains genetic material. The nucleus is typically enclosed by a double membrane called the nuclear envelope, with nuclear pores that regulate traffic between nucleus and cytoplasm. Inside is chromatin, composed of DNA and proteins; during cell division, chromatin condenses into chromosomes. The nucleolus, inside the nucleus, synthesizes ribosomal RNA and assembles ribosomal subunits. The nucleus coordinates gene expression and DNA replication, guiding the cell cycle. Transcripts produced in the nucleus are processed and exported for translation in the cytoplasm. Most organisms with nuclei (eukaryotes) have a defined nucleus, while prokaryotes lack one, and some cells are multinucleated, such as certain muscle fibers and fungal hyphae.