Biology 1002B Lecture Notes - Circadian Rhythm, Northern Blot, Suprachiasmatic Nucleus

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Published on 21 Apr 2013
School
Western University
Department
Biology
Course
Biology 1002B
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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 constant rhythm)
6. Mechanism of oscillating gene expression in Neurospora biological clock (FRQ expression)
Every living thing have clocks and neurospora has frq clock gene
o The change in transcription and translation of frq gene is what oscillates/ keeping time in clock
WC1 and 2 bind to promoter of frq as positive elements that activate transcription
o Max mRNA transcription abundance around 10 am
o Max protein abundance around 3:30 pm (translation takes time so max appears later)
Frq protein is a negative elements that inhibits its own transcription by switching off WC 1 and 2
o Frq gets phosphorylated by a specific kinase
o Degrades slowly until there is none or not enough to inhibit transcription
Photoreceptor can affect WC 1 and 2 (entrain)
Oscillation controlled by positive and negative elements
7. Use of psbA reporter gene in cyanobacteria to measure gene expression.
PsbA photosynthetic gene under circadian control
Took promoter of psbA and fused it to lux gene
Lux gene placed into cyanobacteria that already has one copy of this
Lux gene makes luciferase protein that produces bioluminescence light
o Measure amount of light to measure transcript instead of using Northern Blot
Mutants rhythm is shorter or longer
o Not in psbA but in clock gene that influences psbA
8. How to determine the advantage to having a biological clock matching the environment
Clock is more closely to external environment advantage

Document Summary

Clock set/reset by external environment astronomical time: clock not totally independent of environment and entrain to external light. If environment is constant, the clock still works (free running: 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: not only a response to light because it is a circadian rhythm (anticipates light, ways to distinguish circadian from non-circadian diurnal rhythms. Photosynthesis the process is not circadian (needs sunlight) Dna replication has circadian rhythm but why does it tend to occur at night: evidence that circadian clocks are genetic. E. g. eclosion mutants show period identified by peaks is either shorter or longer (no constant rhythm: mechanism of oscillating gene expression in neurospora biological clock (frq expression) Every living thing have clocks and neurospora has frq clock gene: the change in transcription and translation of frq gene is what oscillates/ keeping time in clock.