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The Structure of Black
Hair
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We will begin by defining the African American hair. Black 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 together form a "polypeptide chain". Black hair has
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 atom of one amino acid extending to bond with the nitrogen
atom of the next amino acid.- The 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".
These macrofibrils are grouped together to form the cortex (or the
main body) layers of the hair fiber. Packed dead cells surround
these structures and are known as the cuticular layers of the hair.
In the center of these structures lies the medullary canal, which is
actually apart of the excretory system and houses any foreign
debris, heavy metals, synthetics and medications that are thrown off
by the body and eventually released through the canal.
- 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. As we stated earlier,
keratin protein begins with an alpha helix building into
protofibrils, microfibrils, macrofibrils, then cortex layers. The
bonds in the hair are located within each and every alpha helix.
- The Hydrogen Bond
- The first bond we will discuss is
the hydrogen bond. This bond is located between the coils of the
alpha helix and is responsible for the ability of the hair to be
stretched elasticity) and return back to its original shape. The
hydrogen bonds allow us to change the shape of the hair temporarily
with the aid of water. These bonds are electrolytically controlled
and are the most readily broken down and the most readily reformed.
These bonds are responsible for approximately 35% of the strength of
the hair and 50% of the hair's elasticity (some would argue up to
99.9% of the hair’s elasticity).
- 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 00C- group) to the
side chain of an acidic amino acid, i.e. NH3+. (This is two positive
and negative charges attracting one another.) This occurs in a
position paralleled to the axis line of the rotation of the helix of
the hair. The salt bond is responsible for approximately 35% of the
strength of the hair and 50% of the hair's elasticity.
- 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. Because of its position in the hair,
it is responsible for the hair's toughness or abrasion resistance.
(It actually holds the hair fibers together.) These cross-links are
frequent in the hair fiber, with maximum of frequency of one cystine
bond every four turns of the alpha helix. This is what enables us to
permanent wave the hair.
- 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. Because of its position, it gives the hair toughness but
little strength (5%). Some moisture is contributed to the hair as a
by-product of this bonding.
- Isn't hair fun! :) whewww!
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