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Figure 4 | Theoretical Biology and Medical Modelling

Figure 4

From: A model for generating circadian rhythm by coupling ultradian oscillators

Figure 4

Entrainment of the circadian oscillator by 24-hour light-dark cycles. During 12-hour periods of light and dark, the circadian oscillator (D5) shows a 24 hour period, owing to a presumed light-activated protease that degrades the products of the driving oscillators. "Light" was represented by a function, L, that varied between 0 (dark) and 1 (light), and was linked to the degradation of the light-sensitive proteins P2 and P4 (see text) through the coupling constant k29. The function used to represent the light/dark cycle was : L = {|sin(2πt/24)|.05 •sign(sin(2πt/24))+1}/2 where t is the time in hours and "sign" is the defined by sign(x) = -1 when x < 0, = 0 when x = 0, and = 1 when x > 0. The effect of light (L = 1) is to decrease the half-lives of proteins P2 and P4 from 10 minutes to just over 5 minutes.

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