nucleus

In physics, the positively-charged central part of an atom, which constitutes almost all its mass. Except for hydrogen nuclei, which have only one proton, nuclei are composed of both protons and neutrons. Surrounding the nucleus are electrons, of equal and opposite charge to that of the protons, thus giving the atom a neutral charge. Nuclei that are unstable may undergo radioactive decay or nuclear fission. In all stars, including our Sun, small nuclei join together to make more stable, larger nuclei. This process is called nuclear fusion.

The nucleus was discovered by the New Zealand-born British physicist Ernest Rutherford in 1911 as a result of experiments in firing alpha particles through very thin gold foil.

A few of the particles were deflected back, and Rutherford deduced that the deflection was due to the positively charged alpha particles being repelled by approaching a small but dense positively charged nucleus.

nucleus

Typical plant and animal cell. Plant and animal cells share many structures, such as ribosomes, mitochondria, and chromosomes, but they also have notable differences: plant cells have chloroplasts, a large vacuole, and a cellulose cell wall. Animal cells do not have a rigid cell wall but have an outside cell membrane only.

The nucleolus is found in the nucleus. It contains the nucleolar organizers, the regions on some chromosomes containing genes that code for ribosome synthesis. An average, healthy cell can produce up to 10,000 ribosomes per minute.

In biology, the central, membrane-enclosed part of a eukaryotic cell, containing threads of DNA. It is found in both plant and animal cells. During cell division the threads of DNA coil up to form chromosomes. The nucleus controls the function of the cell by determining which proteins are produced within it. It is where inherited information (see inheritance) is stored as genes. Because proteins are the chief structural molecules of living matter and, as enzymes, regulate all aspects of metabolism, it may be seen that the genetic code within the nucleus is effectively responsible for building and controlling the whole organism.

The nucleus contains the nucleolus, the part of the cell where ribosomes are produced. Movement of molecules into and out of the nucleus occurs through the nuclear pores. An average mammalian nucleus has approximately 3,000 pores.

nucleus

In astronomy, compact central core of a galaxy, often containing powerful radio, X-ray, and infrared sources. Active galaxies have extremely energetic nuclei.