Rate of Synthesis of Hair -Keratin Hair grows at a rate of 15 to 20 cm/yr. All t
ID: 188349 • Letter: R
Question
Rate of Synthesis of Hair -Keratin Hair grows at a rate of 15 to 20 cm/yr. All this growth is concentrated at the base of the hair fiber, where -keratin filaments are synthesized inside living epidermal cells and assembled into ropelike struc- tures (see Fig. 4-11). The fundamental structural element of a-keratin is the helix, which has 3.6 amino acid residues per turn and a rise of 5.4 Å per turn (see Fig. 4-4a). Assuming that the biosynthesis of -helical keratin chains is the rate-limiting factor in the growth of hair, calculate the rate at which peptide bonds of -keratin chains must be synthesized peptide bonds per second) to account for the observed vearly growth of hairExplanation / Answer
length of an amino acid in alpha helix = 5.4angstorm/3.6aa = 1.5 angstorm/aa
given that, rate of growth = 20cm/year = 20cmyr-1/365days yr-1 * 24 hr day-1 * 60min hr-1 * 60sec min-1
= 6.3 * 10-7cm/sec
= 6.3 * 10-9 m/sec
now, rate of protein synthesis = 6.3 * 10-9m sec-1 / 1.5 * 10-10m aa-1 = 42 amino acid / second.
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