Lecture 1 - Introduction to clocks Flashcards
What are some selective pressures?
sunlight, temperature, climate, predation, sexual pressures, social interaction.
what does circadian mean?
roughly a day, 20-28hours.
what are the features of a circadian clock?
responsive to the environment, ie food, light, temperature, social contact.
self sustained oscillation.
relevant to the environment - roughly 24 hours.
drives rhythmic outputs.
what are the following properties clock:
period amplitude phase entrainment free running rhythm
period - clock speed, species specific.
amplitude - magnitude difference between peak and trough.
phase - temporal alignment relative to environment.
entrainment - stable phase relationship with environmental signal. entraining signal provided by zeitgeber.
free running rhythm - natural function of clock when entrainment removed.
period of mice, hamster and human clocks?
mice - 23.7 hours.
human - 24.5 hours.
hamster - just over 24 hours.
dominant zeigeber for most organisms?
light
good marker for circadian clock in hamsters?
wheel running.
how is the re-setting response characterised?
Phase response curve.
Irrespective of whether the organism is Nocturnal or Diurnal, light only re-sets the clock during the hours of subjective darkness.
Light early in S/night : DELAYS
Light late in S/night : ADVANCES
Light in S/Day : No response – dead zone
Clock is “gated” and won’t respond to light in the subjective day.
what is the effect of SCN lesion?
Destruction of the SCN causes loss of behavioural circadian rhythmicity.
Can still respond to external stimuli, ie LD is fine, but once DD it’s arythmic.
how is the clock related amonsgst all animals?
Genome Analysis - the basic building blocks of the molecular clock are conserved between all animals
Describe the feedback loop of the mammalian circadian clock.
CLOCK + BMAL1 heterodimatise (and act on E-box?) and drive transcription of period + crytochrome.
PER + CRY accumulate and heterodimerise, inhibiting CLOCK + BMAL activity.
Decrease in CRY + PER, they are targetted to be broken down/degredation.
Casein kinase 1 ε/δ - phosphorylates PER to speed up degredation of
what sets the speed of the clock?
Casein Kinase 1 ε/δ through phosphorylation of PER
how does the clock drive rhythmic experssion of non clock genes?
directly via E-Box, RORE, D-box sites.
Indirectly via chromatin structuring
Master clock
SCN
Suprachiasmatic nuclei.
located in the anterior hypothalamus, just above the optic chiasm, bilateral to either side of the third ventricle.
Peripheral oscillators
almost all tissues.
