Hair grows when stem cells at the divide; the cells become keratinized and die as they are pushed up
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Human hair grows in a cycle that includes a growth phase and a rest phase. A small fraction of the hairs on the scalp are in the rest phase, while the majority of the hairs on the scalp are in the growth phase, which allows the hair on the scalp to grow long. Conversely, the majority of hairs in areas such as the eyelashes are in the rest phase, which keeps those hairs short.
Crystal W.
Supreeta N.
Hair grows at a rate of 15 to 20 cm/yr. All this growth is concentrated at the base of the hair fiber, where α-keratin filaments are synthesized inside living epidermal cells and assembled into rope-like structures. The fundamental structural element of α-keratin is the α helix, which has 3.6 amino acid residues per turn and a rise of 5.4 Å per turn. Assuming that the biosynthesis of α-helical keratin chains is the rate-limiting factor in the growth of hair, calculate the rate at which peptide bonds of α-keratin chains must be synthesized (peptide bonds per second) to account for the observed yearly growth of hair.
David C.
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