Biological clock
This lecture note is from 2010. Time flies so fast
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เป็นการเขียนสรุปส่งหลังจากนั่งฟัง Special Lecture (ส่วนหนึ่งของวิชา cell science) เห็นว่ามันน่าสนใจ และน่าจะมีประโยชน์แก่คนที่เข้ามาอ่าน เลยเอามาลงไว้ด้วย หัวข้อนี้ อ. Nateetip จากภาควิชา Physio คณะวิทย์ เป็นคนบรรยาย
Biological Clock or Circadian Clock
Biological clock is the regular pattern of changes in biological processes (biochemical, physiological and behavioral) of an organism that occurs within a period of time and in a particular surrounding. It is an endogenous process that the pattern of changes does not depend on the external cues such as light. Though, it is known that the biological clock is determined by genetic factor (endogenous), it must be entrained or reset by the environmental factors. Therefore, the biological clock is important for the organisms to survive, by the mean that it organizes the time course of biological processes in order to respond correctly to the changing environmental conditions.
In mammals, it is believed that the SCN (suprachiasmatic nucleus) is the main circadian clock which is located in the anterior hypothalamus. Moreover, it appears that the molecular mechanism of the circadian clock is controlled by the feedback loop that is comprised of positive and negative element(s) as shown in figure 1. This feedback loop is thought to be conserved among the phyla.
Figure1. With the certain level of negative element(s), it inhibits the function of positive element(s). Once the concentration of the negative element(s) drops, a new cycle starts again. (Figure from: Molecular Bases for Circadian Clocks, Cell, Vol. 96, 271–290, January 22, 1999)
Light is the primary environmental factor that entrains the biological clock. Although, the hypothalamus is not directly exposed to the light, it is indirectly regulated through the signal from retino-hypothalamic tract. It is known that the functions of hypothalamus influence various activities of biological processes, for instance, sleep, body temperature, hunger and hormone release. Therefore, the SCN is appeared to synchronize the biological clock throughout the body to the natural cycle of day length. For example, highly expressed melatonin can promote our body to go to sleep, therefore, the highly expression of melatonin is appeared only at night (normal time for sleeping). The expressed activity of melatonin is showed to be regulated by the cascade of signal from retina (dark sensing)--SCN--pineal grand and then induction of melatonin expression.
Several human activities can disturb the circadian clock, for example, shift work and jet lack, these two situations result in the discordance between the biological processes in our body and the responsible task. Additionally, mutations of the gene-related to circadian clock can also cause diseases and metabolic alteration.
*circadian = 24 hrs. therefore circadian biological clock refers to the changing of biological processes within 24 hrs.
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เป็นการเขียนสรุปส่งหลังจากนั่งฟัง Special Lecture (ส่วนหนึ่งของวิชา cell science) เห็นว่ามันน่าสนใจ และน่าจะมีประโยชน์แก่คนที่เข้ามาอ่าน เลยเอามาลงไว้ด้วย หัวข้อนี้ อ. Nateetip จากภาควิชา Physio คณะวิทย์ เป็นคนบรรยาย
Biological Clock or Circadian Clock
Biological clock is the regular pattern of changes in biological processes (biochemical, physiological and behavioral) of an organism that occurs within a period of time and in a particular surrounding. It is an endogenous process that the pattern of changes does not depend on the external cues such as light. Though, it is known that the biological clock is determined by genetic factor (endogenous), it must be entrained or reset by the environmental factors. Therefore, the biological clock is important for the organisms to survive, by the mean that it organizes the time course of biological processes in order to respond correctly to the changing environmental conditions.
In mammals, it is believed that the SCN (suprachiasmatic nucleus) is the main circadian clock which is located in the anterior hypothalamus. Moreover, it appears that the molecular mechanism of the circadian clock is controlled by the feedback loop that is comprised of positive and negative element(s) as shown in figure 1. This feedback loop is thought to be conserved among the phyla.
Figure1. With the certain level of negative element(s), it inhibits the function of positive element(s). Once the concentration of the negative element(s) drops, a new cycle starts again. (Figure from: Molecular Bases for Circadian Clocks, Cell, Vol. 96, 271–290, January 22, 1999)
Light is the primary environmental factor that entrains the biological clock. Although, the hypothalamus is not directly exposed to the light, it is indirectly regulated through the signal from retino-hypothalamic tract. It is known that the functions of hypothalamus influence various activities of biological processes, for instance, sleep, body temperature, hunger and hormone release. Therefore, the SCN is appeared to synchronize the biological clock throughout the body to the natural cycle of day length. For example, highly expressed melatonin can promote our body to go to sleep, therefore, the highly expression of melatonin is appeared only at night (normal time for sleeping). The expressed activity of melatonin is showed to be regulated by the cascade of signal from retina (dark sensing)--SCN--pineal grand and then induction of melatonin expression.
Several human activities can disturb the circadian clock, for example, shift work and jet lack, these two situations result in the discordance between the biological processes in our body and the responsible task. Additionally, mutations of the gene-related to circadian clock can also cause diseases and metabolic alteration.
*circadian = 24 hrs. therefore circadian biological clock refers to the changing of biological processes within 24 hrs.
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