All amino acids contain amine (-NH2), carboxyl (-COOH) and R group (side chain) with hydrogen (H).
All of the 20 amino acids coded by genetic code have N-terminus (amine) and C-terminus (carboxyl) and those are called functional groups. The key components of amino acids are hydrogen, oxygen, carbon and nitrogen. They can be classified in different subgroups according to their polarity, the core structural functional groups, side chain group type, pH.
-Each amino acid consists of a central carbon atom (the α carbon) bonded to a hydrogen atom, a carboxyl group, an amino group, and a specific side chain (designated R).
-Amino acids have a two-carbon bond. One of the carbons is part of a group called the carboxyl group (COO-). A carboxyl group is made up of one carbon (C) and two oxygen (O) atoms. That carboxyl group has a negative charge, since it is a carboxylic acid (-COOH) that has lost its hydrogen (H) atom.
Through the thin walls of the capillaries, oxygen and nutrients pass from blood into tissues, and waste products pass from tissues into blood. From the capillaries, blood passes into venules, then into veins to return to the heart.