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Lecture

Lecture 24.docx

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School
Western University
Department
Biology
Course
Biology 1002B
Professor
Tom Haffie
Semester
Winter

Description
Lecture 24: Biological Timekeeping  Circadian clock  Diurnal Phenomena o Reoccurs daily  Foraging/predatory behaviour  Sleep-wake cycles  Body temperature  Hormone secretion  Photosynthesis o It acts like a sine function, goes up and down  The value of keeping track of time o What if organisms could anticipate environmental change?  Know when sun goes up and down  Think of advantage  Conserve energy o Lhcb2 mRNA  Photosynthetic gene, light antenna around PSII  There’s no transcript during the night, only appears during the day  Measure transcript abundance, using northern blot  Transcription vs. mRNA decay  This is not a response to light, because it begins to synthesis when it is still dark  It anticipate that light is going to come on  The transcript abundance start when it is still dark o It is continued under constant light  The cycle continues with constant light o How can you explain this?  Not just response to light  Endogenous biological clock  Circadian rhythm  Question: what is the advantage of anticipation (check online)  Circadian rhythms o Circadian rhythm – biological rhythm with a period of “around” a day (24 hours) sometimes more sometimes less o Based on internal clock o Two major criteria  Can be set by the external time (environment)  Can be set of what is going on outside, can be based on the sun  Free-running  Not slaved to the external time  So when environment is constant, the cycle continues, it runs by itself  Eventually, the free-running clock can get out of whack, must be trained again  E.g. body temperature and hormone under circadian control, even under constant environment  Circadian phenomena o Diurnal phenomena  Circadian  Non-circadian o Photosynthesis (the process) (light depended, not circadian) vs. photosynthetic gene expression (under circadian control) o Thousands of genes are under circadian control  Questions about the clock o Has a clock o Input  How is the clock synchronized with astronomical time? o Output  How is molecular time linked to changes in physiology/behaviour o What is the biochemical basis of the clock o Every clock oscillators, moves between two extremes passing an equilibrium  The period is very constant  Circadian rhythm have a genetic basis o Drosophila melanogaster o Eclosion mutants (when larva turns into a fly)  The mutants
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