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Lecture 24.docx

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Western University
Biology 1002B
Denis Maxwell

Lecture 24: Biological Timekeeping 1. Jet Lag  Central biological clock found in suprachiasmatic nucleus (SCN) out of circadian cycling synchronization o Receive direct light inputs through optic nerve of the eye so that is can be reset periodically o Regulates clock timing in peripheral tissue through release melatonin from pineal gland at night 2. Examples of diurnal physiological/behavioural rhythms  Foraging/predatory behaviour  Sleep/wake cycles  Body temperature and hormone secretion  Photosynthesis 3. Characteristics of circadian rhythms  24 hour biological rhythm  Clock set/reset by external environment – astronomical time o Clock not totally independent of environment and entrain to external light  If environment is constant, the clock still works (free running) o Body temperature and hormone secretion in circadian rhythm even in constant darkness  Northern Blot of mRNA transcript abundance shows that photosynthetic gene is expressed in dark o Not only a response to light because it is a circadian rhythm (anticipates light) 4. Ways to distinguish circadian from non-circadian diurnal rhythms  Photosynthesis the process is not circadian (needs sunlight)  Photosynthetic gene expression is circadian  E.g. DNA replication has circadian rhythm but why does it tend to occur at night? 5. Evidence that circadian clocks are genetic  E.g. eclosion mutants show period identified by peaks is either shorter or longer (no constan
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