Explain in details Amino Acid?

Amino Acids :  There are 20 common amino acids, with a few more found in lower organisms. Adult humans require a diet that includes at least 8 essential amino acids because humans are unable to synthesize them. The human body is able to synthesize the rest of the amino acids. Each amino acid differs from the others by variations in a side-chain called an R-group. The R-group can be positively or negatively charged, polar (electrically asymmetrical) or non-polar (electrically symmetrical).

Amino acids join to each other by condensation (also referred to as dehydration) reactions between the negatively charged carboxyl group and the positively charged amino group of successive amino acids in the chain. In a condensation reaction, the reactants give off H+ and OH-, which combine to form water. The opposite reaction, in which H+ and OH- from water is added to each of the monomers to break down the molecule, is called hydrolysis.