brasheranatomychemistry

CHEMISTRY OF THE BODY

Atoms are the building blocks of matter. They consist of a nucleus, which contains protons and neutrons, and an electron cloud, which contains electrons. These electrons are arranged in energy levels around the nucleus. The first energy level may contain as many as two electrons, the second level can hold eight, the third level eighteen, and so on. The electrons in the outer energy level are called //valence electrons// and may be gained or lost to form charged //ions. Cations// are ions which are positively charged because they have lost one or more electrons. //Anions// are ions which are negatively charged because they have gained one or more electrons. Ions combine to form compounds such as salt (NaCl). This is called ionic bonding. Atoms can also share electrons to form molecules such as water, sugars, proteins, and fats. This is called covalent bonding.

CELLS

Cells are the smallest units of all living things. They are made up of several common structures: Smooth ER--aids in the synthesis and breakdown of cholesterol, in fat metabolism, and in the breakdown of drugs.**
 * Nucleus--The nucleus of a cell is NOT the same as the nucleus of an atom. A cell nucleus contains many atoms which combine together to form a large molecule called DNA. DNA contains the genetic code for your cells.
 * Ribosomes--Protein synthesis takes place here.
 * Endoplasmic Reticulum (ER)--This is a system of canals within the cell which is responsible for carrying substances from one part of the cell to another.
 * Rough ER--Transports proteins throughout the cell which have been produced by ribosomes located on its surface.
 * Golgi Apparatus--This stack of membrane packages proteins for transport outside the cell or to various structures inside the cell.
 * Lysosomes--These are sacs containing digestive enzymes.
 * Mitochondria--These organelles are the site of ATP production. ATP provides energy for all body functions.
 * Centrioles--These are paired, rod-shaped structures which function in mitosis (cell division) in animals.
 * Cell (Plasma) Membrane--This structure encases the semifluid gel, //or cytoplasm//, found within the cell. Its main function is to regulate the passage of substances into or out of the cell.