Cross-bonds (Side-bonds)
Design Essential (2024) stated that hair’s composition consists of many factors, such as raw elements, amino acids, bonds, and proteins. COHNS are the primary building blocks of protein within hair. Other traces of amino acids are found in hair fibers and assist in producing healthy hair. Hairfinder (2024) reported that humans’ amount of amino acids varies. At least 16 amino acids are present in human hair, each very small in molecular size. See Figure 2. The primary function of amino acids is to bond together and build protein chains within every body cell. Human hair production involves peptide bonds joining amino acids: carbon, oxygen, hydrogen, nitrogen, and sulfur, known as COHNS, end to end. Due to their function, peptide bonds are also called end-bonds. Multiple peptides join amino acids, creating chain-like linkages (protein chains), also known as polypeptide chains (Design Essentials, 2024; Hairfinder, 2024; Lopez & Mohiuldin, 2023; Milady, 2023). Amino acids found in hair fibers Figure 2: Other Amino Acids Found in Hair Fibers Amino Acids Percentage Cysteine 17.5% Serine 11.7% Glutamic acid 11.1% Threonine 6.9% Glycine 6.5% Leucine 6.1% Valine 5.9% Arginine 5.6% Aspartic acid 5.0% Alanine 4.8% Proline 3.6% Isoleucine 2.7% Tyrosine 1.9% Phenylalanine 1.4% Histidine 0.8% Methionine 0.5% Polypeptide chain Figure 3: Amino acids (COHNS) Joined by Peptides (End-bonds) to Create a Polypeptide Chain
Figure 4: Cross-bonds Connect Amino Acid Side-to-Side Among Polypeptide Chains
Note . Proprofs.com
Like amino acids, side-bonds consist of elements; the components making up the chemical composition of cross- bonds are hydrogen, salt, and sulfur (disulfide). Side bonds are the strongest bonds within the structure of human hair. They determine the durability and manageability of the hair, accounting for approximately 33% of the hair’s overall strength and elasticity. Cross-bonds create a strong network of proteins, reinforcing the vigor and healthfulness of hair fiber (Toscani & Fino, 2024; Milady, 2023). Hydrogen, salt, and sulfur bonds are the primary protein elements in cross-bonds. The three bonds have natural characteristics that affect how hair reacts to environmental conditions (Toscani & Fino, 2024; Milady, 2023). Each cross- bond plays an active role in the hair’s responses to hair care products, implements, and hair services, such as wet setting, thermal styling, blow-drying, chemical relaxing, and permanent waving (Milady, 2023). Hydrogen and salt bonds are the weakest bonds among the three, yet they make up two-thirds of hair’s strength and elasticity. They are physical and facilitate temporary changes within the hair strand. Examples of physical properties and temporary changes include the hair having a specific look when dry, changing in size and physical characteristics when wet, and reverting to the original look when dried (Toscani & Fino, 2024; Milady, 2023). Hydrogen bonds cross-link two hydrogen amino acids. They are the major bonds responsible for changes in the hair’s shape during heat applications or when wet, taking different forms in each instance. This means that natural bonding is temporarily altered due to adding extra hydrogen elements in water and the decrease of hydrogen elements caused by heating. Hydrogen bonds provide up to 30% of hair’s strength and up to 50% of hair’s elasticity (Toscani & Fino, 2024; Milady, 2023).
Millions of polypeptide chains make up individual hair strands. Polypeptide chains are long, coiled, and spiral- shaped proteins called a helix. Polypeptide chains intertwine, forming the shape of a helix. Within the helix formation of millions of polypeptide chains, a cross-linking of the chains occurs by the bonding of amino acids side to side, by elements known as side-bonds. (Milady, 2023).
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Book Code: CIL0725
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