circadian rhythms Flashcards
why do animals have circiadn rhythms?
because there are regular light dark cycles on the planet but also they day length changes so needs to to be reset because not exactly 24 hours- eery morning it is set
- this is called being entrained
what is it called when the CR gets reset every day by the sun?
being entrained
what happens when you put a mouse in the dark?
free runs- so do people
where is the mammalian clock?
in the suprachiastmatic nucleus?
how was the area of the brain with the clock first found?
by carrying out lesions and using gerbils and seeing when there entrainment stops
how was it discovered that the SCN was THE clock area, not just getting signals from somewhere else in the brain?
a mutant hamster with a mutant cycle was found and make homozygous- if you cut the SCN and put it int WT then the WT suddenly has a mutant clock- and vice versa- so must be the SCN
what was the very first sign that mammals become entrained via their eyes?
if you remove the eye in animals they lose their entrainment
what was the experiment which showed that the resetting circuit in the eye was not rods or cones?
- they produced a mutant cone mouse and clock was fine
- produced a mutant cone and was fine
- double mutant was fine
how was it shown that there was s circuit from the eye to the SCN and back to the other eye?
they used rabies which is a retrovirus and tagged it and saw it went all the way back to the SCN and then back again to the opposite eye
what is the photopigment in the cells that do the reseting?
melanopsin- did a antibody on the eye for it
how was the clock gene first found?
they did a huge mouse screen using wheels and found a mutant with a fast clock when free running and then made a homo and was mutant completely
- the then used linkage to find the gene and called it clock
how did the structure of the clock gene demonstrate its functioning?
it has a basic helix loop helix structure showing it is a transcription factor binding DNA, also a glutamine rich tail which shows it was activating gene expression
explain the molecular mechanism behind the clock gene
it binds to a partner protein called blame and forms a dimer- this drives the expression of a set of genes called the ‘period genes’
- there is a 6 hour delay between binding and turning the period genes into proteins
- per and cry will bind and form a stable dimer
- however, these monomers are also targeted for degradation by casein kinase which slows down the process
- but once enough dimers have formed they enter the nucleus and bind to clock and bmal1 and prevent them from binding and turns off their own expression- until low enough for cycle to start again
how did they find that the clock gene was expressed in places other than the pineal gland (SCN) in the fish?
they were looking at the expression mRNA in a light dark cycle in the pineal
- took out controls from other parts of the brain and found was also oscillating here
- then found it was also oscillating in the rest of the organs
- then found it could be entrained in the organs!
what happened when they took cells populations and kept them in a dark dark cycle and why did they think this as bad- how did they rescue?
- the cells stopped showing oscillations
- thought this was bad because of they lose their clock- so no inherent
- but then they thought thy amass all be out of sync- resolution gin a average no change
- so they did luminescent of single cells and found that they were all out of sync in the DD but still oscillating but could be snapped back in to cycle with a light pulse- this is what happens to humans
