The Advanced Architecture of the Cell - Bioengineering: A Conceptual Approach - page 8

concentrations but are of vital importance (Br, Cr, Co, Cu, F, I, Fe, Mn, Mo, Se, Si,
Sn, V, and Zn). Elements can compose the compounds in a fixed ratio, and with dif-
ferent properties than the elements alone have (Nalco is different than either Na or
Cal). Dependent on the types of bonds and the size of molecules, the compounds
can be micro (water and salt bonds-inorganic matter) and/or macromolecules (C-C
or CONH bonds-organic matter) [ 2 ].
The behavior of the element is determined by the structure of the atoms that are
building the element. The atom is the smallest possible unit of matter that retains the
physical and chemical properties of its element. Atoms are tiny particles, not visible
by naked eyes. Atoms of the same element share similar chemical properties. Atoms
are made up of subatomic particles, the three of which—the most stable are: neu-
trons (no charge, neutral), protons (positive charge), and electrons (negative charge).
If an atom is electrically neutral, the number of protons equals the number of elec-
trons, which yields an electrostatically balanced charge. They are further divided in
smaller particles known as subatomic, or elementary particles. Today we know that
hundreds of elementary particles have been discovered (neutrino, mesons, moons,
positrons).
These elementary particles are made up of extremely small particles called
quarks. But the quarks, even so small, have their own organization. According to
Gel Man's system of symmetry, there are quarks and antiquarks, matter and anti-
matter (of the opposite charge). There are 4 different kinds of quarks which
are = 2/3,-1/3,-1/3, = 2/3 that of the electron charge. The quarks combine to make
different elementary particles. Each meson, for example, can be conceived as the
union of quark and antiquark. Knowing these entities is necessary for example for
development of nanotechnology-nanoparticles that can improve some function in
the body or be of diagnostic or curative importance.
In atom, e.g. element, number of protons is constant while the number of neu-
trons can vary. All atoms of an element have the same atomic number (number of
protons in an atom of particular element). In a neutral atom the number of protons
is equal to number of electrons. The number of protons and neutrons in an atom is
known as mass number. The mass of proton and the mass of neutron are both about
1 . The atom of an element which has the same atomic number but different mass
number is called isotope (same number of protons but different of neutrons). Some
isotopes are radioactive. These are instable, with the spontaneously decaying
nucleus, emitting subatomic particles and/or energy as radioactivity . The use of
isotopes in biomedical sciences is of great importance for radioactive labeling of
substances in many assay designs, determination of the age of fossils, etc. [ 1 ].
Electrons are also important from many aspects, especially valence electrons
(electrons in the outermost energy shell-valence shell since they tend to fill incom-
plete valence shells by interacting with other atoms. This is the reason for creating
chemical bonds—attractions that hold atoms together. Examples of bonds are: cova-
lent, ionic, metallic, hydrogen, and van der Waals.