- The nucleus is the center core of an atom that has a positive charge and that contains most of the atom's mass, or the central heart of an organization or group.
- An example of a nucleus is the center core of an atom.
- An example of a nucleus is the fiction department of a book publisher where most of the money is made and which is considered the heart of the publisher's organization.
- a thing or part forming the center around which other things or parts are grouped or collected; core
- anything serving as a center of growth or development: the nucleus of a library
- Anat. a group of nerve cells in the brain or spinal column
- Astron. the bright central part of the head of a comet
- Biol. the central, usually spherical or oval mass of protoplasm present in most plant and animal cells, containing most of the hereditary material and necessary to such functions as growth, reproduction, etc.
- Bot. the central point in a starch grain
- Chem., Physics the central part of an atom, the fundamental particles of which are the proton and neutron, except for hydrogen, which is usually composed of one proton only: it carries a positive charge and constitutes almost all of the mass of the atom
- Phonet. the most sonorous portion of a syllable, usually a vowel
- Organic Chem. a fundamental, stable arrangement of atoms that may occur in many compounds by atomic substitution without structural change, as the benzene ring
Origin: ModL from L, a nut, kernel, for nuculeus, diminutive from nux (gen. nucis), nut
Used by arrangement with John Wiley & Sons, Inc.
noun pl. nu·cle·i or nu·cle·us·es
- A central or essential part around which other parts are gathered or grouped; a core: the nucleus of a city.
- Something regarded as a basis for future development and growth; a kernel: a few paintings that formed the nucleus of a great art collection.
- Biology A large, membrane-bound, usually spherical protoplasmic structure within a living cell, containing the cell's hereditary material and controlling its metabolism, growth, and reproduction.
- Botany a. The central kernel of a nut or seed.b. The center of a starch granule.
- Anatomy A group of specialized nerve cells or a localized mass of gray matter in the brain or spinal cord.
- Physics The positively charged central region of an atom, composed of protons and neutrons and containing almost all of the mass of the atom.
- Chemistry A group of atoms bound in a structure, such as a benzene ring, that is resistant to alteration in chemical reactions.
- Astronomy a. The central portion of the head of a comet.b. The central or brightest part of a nebula or galaxy.
- Meteorology A particle on which water vapor molecules accumulate in free air to form a droplet or ice crystal.
- Linguistics The part of a syllable having the greatest sonority. In the word middlemost (mĭdˈl-mōstˌ) the nuclei of the three syllables are (ĭ), (l), and (ō); in the Czech word krk (“neck”), the nucleus is (r).
Origin: Latin nuculeus, nucleus, kernel, from nucula, little nut, diminutive of nux, nuc-, nut.
nucleus - Cultural Definition
nucleus - Medical Definition
noun pl. nu·cle·us·es or nu·cle·i
- A large, membrane-bound, usually spherical protoplasmic structure within a living cell, containing the cell's hereditary material and controlling its metabolism, growth, and reproduction. Also called karyon.
- A membraneless structure in microorganisms that contains genetic material but does not itself replicate. Also called nucleoid.
- A group of specialized nerve cells or a localized mass of gray matter in the brain or spinal cord.
- The substance around which a urinary or other calculus forms.
- The positively charged central region of an atom that is composed of protons and neutrons and that contains almost all of the mass of the atom.
- A group of atoms bound in a structure, such as a benzene ring, that is resistant to alteration in chemical reactions.
nucleus - Science Definition
Plural nuclei nuclei
- The positively charged central region of an atom, composed of one or more protons and (for all atoms except hydrogen) one or more neutrons, containing most of the mass of the atom. The strong force binds the protons and neutrons, also known as nucleons, to each other, overcoming the mutual repulsion of the positively charged protons. In nuclei with many nucleons, however, the forces of repulsion may overcome the strong force, and the nucleus breaks apart in the process of radioactive decay . The protons and neutrons are arranged in the nucleus in energy levels known as shells analogous to those of the electrons orbiting the nucleus. The number of protons in the nucleus determines the atom's atomic number and its position in the Periodic Table. See more at atom.
- An organelle in the cytoplasm of eukaryotic cells (all cells except prokaryotes) that contains nearly all the cell's DNA and controls its metabolism, growth, and reproduction. The nucleus is surrounded by a pair of membranes called the nuclear envelope , which can be continuous in places with the membranes of the endoplasmic reticulum. The membranes of the nuclear envelope have interconnected pores that allow the exchange of substances with the cell's cytoplasm. The nuclear DNA is wrapped around proteins (called histones) in strands of chromatin , which exists in a matrix known as nucleoplasm (analogous to the cytoplasm outside the nucleus). Just prior to cell division, the chromatin condenses into individual chromosomes, which contain the cell's hereditary information. The nucleus also contains at least one spherical nucleolus , which mainly contains RNA and proteins and directs the construction of the cell's ribosomes. See more at cell.
- a. The solid central part of a comet, typically several kilometers in diameter and composed of ice, frozen gases, and embedded chunks of rock and dust. It is the permanent part of a comet from which the coma and tail are generated as the comet approaches the Sun. See more at comet.b. See galactic nucleus.
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