Key terms realated to Amino Acids (Glossary)

Amino acids : α-Amino-substituted carboxylic acids which is the building blocks of proteins.

R Groups : (1) Formally, an abbreviation denoting any alkyl group.

                  (2)Ocassionally, used in a more general sense to denote virtually any                                       organic substiuent (the R groups of amino acids, for example).

Chiral carbon : Carbon containing four different groups. Their mirror images do not superimpose with each other. This also known as assymetric carbon.

Chiral center : An atom with substiuents arranged so that the molecule is not superimposable on its mirror image.

Chiral compounds :  A compound that contains  an assymetric center (chiral atom or chiral center) and thus can occur in two nonsuperimposable mirror image forms (enantiomers).

Sterioisomers : Compounds that have the same composition and the same order of atomic connections but different molecular arrangements.

Enantiomers : Enantiomers are a special type of sterioisomers that are mirror images of each other  and the requires of a chiral carbon.

Optical Activity :  The capacity of a substance to rotate the plane of plane polarized light.

Levorotatory isomer :  Asterioisomer that rotates the plane  polarized light counterclockwise.

Dextrorotatory isomer :  A sterioisomer that rotates the plane polarized light clockwise.

D,L System : Nearly all biological compounds with a chiral center  occur naturally in only one sterioisomeric form either D or L. This is known as D,L, System.The amino acid residues in proteins are exclusively L-Sterioisomers.

RS System :  RS System is another system of specifying configuration around a chiral center used in the systematic nomenclature of organic chemistry and describes more precisely the configuration of molecules with more than one chiral center.

Absolute configuration :  The configuration of four different substiuent groups around an assymetric carbon atom, in relation to D- and L-glyceraldihyde.

Zwiter ion or dipolar ion :  Zwiterion(or dipolar ion) is a hybrid molecule containing positive and negative ionic groups . 

Isoelectric pH (Symbol pI) :  pI is defined as the pH at which a molecule exists as a zwiterion or dipolar ion and carries no net charge .Thus , the molecule is electrically neutral .