Arginine is an amino acid containing extra nitrogen which makes it very basic i.e. alkaline. It is also known as 2-Amino-5-guanidinopentanoic acid.
Like all amino acids, it has an amino group (-NH2) - blue with 2 white balls - at one end, and a carboxylic acid group (-COOH) - grey, connected to red, and red and white - at the other end. These groups are used to link onto other amino acids by peptide bonds. Between these is the
α- (alpha) carbon to which the 'R' group is attached.
Its 'R' group is the guanidinium group attached to a propyl group -(CH2)3-NH-CNH-NH2, so it contains 3 nitrogen atoms (blue) at the other end of the molecule.
These 3 extra nitrogen containing groups give arginine extra basic characteristics. These groups do not enter into peptide bonds but may ionise and interact with other R groups in the polypeptide chain.