Hair Structure

Hair Structure 

We will begin by defining the hair. Hair is composed primarily of proteins (88%). These proteins are of a hard fibrous type known as keratin. Keratin protein is comprised of what we call "polypeptide chains.” The word, polypeptide, comes from the Greek word "poly" meaning many and "peptos" meaning digested or broken down. In essence, if we break down protein, we have individual amino acids. Many (poly) amino acids joined toget her form a "polypeptide chain". Two amino acids are joined together by a "peptide bond", and the correct number of amino acids placed in their correct order will form a specific protein; i.e. keratin, insulin, collagen and so on. The "alpha helix" is the descriptive term given to the polypeptide chain that forms the keratin protein found in human hair. Its structure is a coiled coil. The amino acids link together to form the coil and there are approximately 3.6 amino acids per turn of the helix (coil). Each amino acid is connected together by a "peptide bond". The peptide bond is located between the carbon atoms of one amino acid extending to bond with the nitrogen atom of the next amino acid.

A Helix Coil: In the organization of a single hair, three "alpha helices" are twisted together to form a "protofibril". This is actually the first fibril structure of the hair. Nine protofibrils are then bundled in a circle around two or more to form an eleven-stranded cable known as the "microfibril". These microfibrils are embedded in an amphorous unorganized protein matrix of high sulfur content and hundreds of such microfibrils are cemented into an irregular fibrous bundle called a "macrofibril".

Bonding in Keratin Protein: When the hair is in its normal unstretched state. It is referred to as A of alpha keratin. The original configuration of the hair is held in place by the bonding found in the cortex layers of the hair. 

The Salt Bond:The salt bond is also an ionic (electrolytically controlled) bond formed by the electron transfer from the side chain of a basic amino group (an amino acid with an coo- group) to the side chain of an acidic amino acid, i.e. NH3+. (This is two positive and negative charges attracting one another.

The Cystine Bond : The cystine bond also known as the disulfide bond, sulfur bond, or just S bond is formed by cross-links between cystine residues (amino acids) of the main polypeptide chains. This bond is perpendicular to the axis of the hair and between the polypeptide chains. 

The Sugar Bond: The sugar bond is formed between the side chain of an amino acid having an OH group and an acidic amino group. This bond is also formed perpendicular to the axis of the hair.