Final answer:
When two alpha helices of keratin interact, they form a stable structure maintained by disulfide bonds, contributing to keratin's elasticity and strength. Water can temporarily disrupt hydrogen bonds, allowing for temporary changes in hair shape. The intricate assembly of alpha helices into protofibrils, microfibrils, and macrofibrils constitutes the macroscopic structure of hair.
Step-by-step explanation:
When two alpha helices of keratin interact, they form a robust structural arrangement that contributes to the mechanical strength and elasticity of keratin-rich tissues such as hair, nails, and the outer layer of skin. The alpha-helices are further stabilized by disulfide bonds from cysteine residues. These disulfide bonds are essential because they can return the alpha-helices to their original positions when any stretching tension is released, giving keratin its characteristic somewhat elastic nature. Additionally, the interaction of alpha helices is significant in the formation of keratin's higher-order structures, with multiple alpha-helices twisting into protofibrils, which then assemble into microfibrils, and eventually bundle together into macrofibrils within hair strands.
Moreover, the stability of keratin's structure is also influenced by hydrogen bonding within the alpha-helices, which can be temporarily disrupted by the introduction of water molecules. This disruption allows the alpha-helices to shift and slide past each other, enabling a temporary change in the shape of hair when it's wet and subsequently dries, resulting in temporary waves. However, the network of disulfide bonds usually maintains the overall structural integrity of keratin over time.