In
physics, the term 'nucleus' refers to the
tiny, extremely
dense core of an
atom, where the
protons and
neutrons are located and bound together by the
strong nuclear force. (BTW: does the
weak nuclear force play a role in
nucleon bonding?)
The nucleus contains practically all of the
mass of the atom, the
orbiting
electrons weighing only 0.00054 (approx.) of the
proton or
neutron rest mass each. The number of protons in the nucleus (
Z) determine the number of electrons in the atom, and thus the
chemical properties of the atom. The number of electrons determines the
radius of the atom (together with the proton charge], and the number of nucleons determines how massive each atom will be. The number of neutrons determines the
stability of the nucleus, and which of a number of
isotopes of an
element that atom is a member of.
In
biology, the term 'nucleus' refers to the all-important
organelle in the
cell which contains the
genetic material, associated
proteins and
enzymes to
transcribe,
repair and
duplicate this material, and a sub-organelle termed the
nucleolus which contains genetic material relating to the
ribosomes of the cell. The nucleus is often referred to as the
brains of the cell, as it controls and directs the cell's operations and processes by releasing
RNA containing instructions for the
synthesis of proteins into the
cytoplasm to direct the ribosomes in protein synthesis.