2010 MAY EXAM
Let‟s discuss the answers here: I‟ve started with 6 questions. Some of them
we have answers for in the term tests. But it would be helpful if we could go
through all the exams with answers all in one place.
Whoever created this googleDoc, a big thanks! it’s been very beneficial for
everyone! The peak number of people participating at one time was 14 people,
which is at least 1/3 of the whole class. LOL
ATTENTION ON BURING Qs [your feedback is greatly appreciated]
* question 20 answers seem to be debatable.
* ALSO anyone have opinions on 19?? we need a little more for 5 marks worth, no?
*lots of ambiguity in the answer for Q15
*What about questions 8-13?
*Q 7 has no answer yet ANSWERS
The diagram in the first slide in Oct 29 (Powerpoint Oct 22B, slide 22) Loop 1.
1) CK1e causes a CRY:PER dimer to form
2) Once dimerized they enter the nucleus
3) This inhibits (-) the TF (Bmal:CLK) and suppresses cry, per, ccgs, rev-erb
4) When ccgs is not suppressed it promotes (+) phosphorylation of PER and
joining to CRY by Ck1 --- doesn‟t ccgs cause Ck1E to phosphorylate PER??
1. rev-erb does joins to something? to reenter nucleus?
2. causes production of bmal1 which becomes a protein?
Assuming that those two little circles are CRY and PER? Thats the best I can
do, idk how much of it is right so if anyone knows whats happening please fix
it. Hopefully it at least gets the ball rolling
Loop 1 - NEGATIVE feedback loop for PER and CRY. PER and CRY inhibit
themselves. Once there is enough of PER and CRY, they turn off transcription.
Loop 2- POSITIVE feedback loop for PER and CRY. (not sure how). NEGATIVE
feedback for Bmal and Rev-ERBa (not sure how) -- anyone know how????
Okay -- I got it!! --------- Bmal POSITIVELY feeds back to PER and CRY because it
is a transcription factor for PER and CRY. Loop 2 NEGATIVELY affects Bmal and
Rev-ERBa because making PER and CRY causes rev-erba to be inhibited. Rev-
ERBa is made from rev-erba and INHIBITS Bmal1 transcription.
just a small correction (I made sure w/ prof on this):Loop II produces rev-erba
gene, which negatively inhibits transcription of Bmal1. Rev-ERBa is produced by the
gene in the nucleus. (the positive sign besides Rev-ERBa refers to other
Here’s the slide all the info is from.
Im good with that explanation.
How in the world did u copy/paste the image?? how come I can‟t paste pictuers using my computer???
I can't either :S..... only from a a link
Oh.. all I did was click SELECT on my PDF and then dragged the rectangle
over the picture and pressed copy.
I have a pretty old mac but I‟m sure they wouldn‟t take that function away. I
don‟t know how to do it on other computers, but I think you press CAPTURE.
that‟s exactly what i did. FAILED TO PASTE AN IMAGE: One or more images could not be
pasted. Images that are on your local disk or in non-standard formats cannot be imported
from lecture on Oct 22B
the tau mutation (1) reduces the rate of phosphorylation of PER protein by CK1e,
and (2) reduces release of CK1e from the PER:CRY transcription factors
...as result, PER:CRY dimers accumulate faster, and so the transcription translation
feedback loop occurs sooner, thus the period is shorter, causing phase advance.
What gene causes the tau mutation?
good question -- i’m not sure
On Wiki it is MAPT gene -- does this sound familiar to anyone?
Or period gene??
never heard of it lol, i find this proff wants you to know things he doesn't specifically
-retina projects to IGL via optic tract [using RHT]
-IGL lesions affects photic responses
-IGL lesion abolishes non-photic phase shifting
-Neuropeptide Y from IGL into SCN causes non-photic shifts [using GHT]
-electrical stimulation of the IGL produces nonphotic phase shifts in hamsters
-bilateral lesions of the IGL in hamsters results in both (1) reduced circadian
response to changes in light intensity in LL, and (2) reduced circadian response to novelty
Remove the tissue from the presumed site and observe whether the
physiology or behaviour measured (squirting) becomes arrhythmic
- Removal of the site would have to cause arrhythmicity.
- replacement should restore rhythms
- when transplanted between species the restored rhythm matches that of the
donor and is distinct from that of the hosts
2) neural gland
3) anterior surface
The nucleus determines the phase and of the circadian rhythm of
The rhythm, however, doesn‟t need the nucleus to be present.
The anucleate algae can reset the phase of the photosynthetic rhythm when
the LD cycle was inverted.
The photosynthetic rhythm persists even after the nucleus is removed.
-nucleus determines the phase of the circadian rhythm of photosynthesis
-but, nucleus is not required for the rhythm, it just determines the phase ...
The fact that theres two types of responses, photic and non-photic?
- idk about this
IS THIS RIGHT??
I‟m not sure.. I‟ve been trying to find the answer
Ithink we should include the two types of oscillators...1) Circadian Executive
oscillator= SCN and 2) Circadian Operations oscillator = peripheral
oscillators.??????and the evidence is the ZT03 and ZT11 experiment. Where
the animal remembers the ZT11 training even when tested at ZT03 after 18
You might be right.. I was also thinking of the fact that we anticipate things
during the day, like eating our lunch. That has nothing to do with the LD cycle
that can entrain our sleep-wake cycle. We talked about this on Nov 14 with
rats. They have an oscillator that anticipates food (and they run on their wheel
in anticipation) which is separate from their sleep-wake cycle. I think what I just said is just an example of what you said. I‟m reading my
notes and it says peripheral oscillators are running when you put a rat on
7. Design an experiment to identify the presence of a circatidal
I believe this has to do with what we covered nov 14th, although I’m not entirely sure
how to answer this. Fireflies synchronize to the full moon. You could take them out
of their natural environment and see that their circadian rhythm is still running, but
their circatidal clock will be arrhythmic.
REALLLY not sure.. Anyone else??
14. How did SCN transplant experiments in hamsters the adaptive significance
of having a clock?
- tau was transferred
-healthy SCN transplanted into old hamsters gave them healthier (less
fragmented) rhythms, and greater longevity
-longer lifespan = more time to reproduce = more likely to have more offspring
15. A population of amphipods (tau = 24) is collected at 9am on a beach in the
Northern Hemisphere with water directly to the W. Indicate the direction of
escape for each assuming they do not immediately see the water (6 points)
a) If the population is released in sunlight?
b) If the population in released with overcast sky?
c) If the population is released after 3 days in constant conditions onto a
beach facing SW in the direct sunlight at 3pm?
d) If the population is transported 3 time zones to the east in constant dark,
then released at 3pm local time?
e) If the population is transported to a sunny beach in the S. Hemisphere
(same time zone) and released the next day at 3pm local time?
f. If the population is transported to a sunny beach in the S Hemisphere and
released 6pm local time?
*assume amphipods move towards land on home beach when no visual cues
a) E b) random
c) SE animal will escape according to home beach (not according to new
- should this be E then? correct
time zones increase as you go east correct? meaning 3pm in an eastern
timezone is 12pm in a western. Therefore the animal thinks its 12 and goes
SE? you are right!
e) E animal try to go to the sun at 3PM, in order to go East. the sun is at NW @
3PM in S Hemi. so the animal moves South.
my reasoning for E here was that its the same time zone so the animal
knows whats up, idk if thats true though. at 3PM: sun is in NW at southern
hemi, but the sun is in SW in northern hemi. If it‟s 3PM in northern hemisphere,
animal goes 135 degree CCW from the sun at SW, in order to reach east. in
southern hemisphere, animal goes 135 degree CCW from the sun at NW, which
f) SE the sunset in the West @ 6PM, which is direction of water. the animal
anyone agree? disagree?
17. Describe 2 primitive reason for having biological clocks.
Anticipation: Preparation for regular changes in the enviroment
Organization: optimal temporal sequncing of molecular, cellular, tissue, and
16. True or False
a. photoreceptors for the mammalian circadian system are located in the
b. a circadian clock in a lizard is always found in the pineal gland.
c. Circadian pacemakers in Bulla are located in the visual retina.
d. mice without eyes do not have circadian locomotor rhythms in LD cycles.
e. A circadian rhythm in cyanobacteria, kai proteins, can be demonstrated in a
f. a sparrow with neither eyes nor pineal cannot synchronize with an LD cycle.
g. A cockroach without optic lobes is rhythmic in DD. h. A fruitfly without PER remains rhythmic in DD.
i. A hamster with bilateral lesions of the IGL cannot entrain to an LD cycle.
j. The melatonin rhythm in humans does not change through the year.
k. the melatonin rhythm in nocturnal and diurnal mammals is inverted (180
degrees out of phase)
l. In mammals, circadian oscillators are found only in the SCN.
e. True? - because Kai A,B and C autophosphorylate, inhibit and promote all
ah ha, you're right.... wikipedia saves the day
http://en.wikipedia.org/wiki/Bacterial_circadian_rhythms - scroll down to
“molecular mechanism of cyanobacterial clockwork”
g. False - slide 31, Oct 10th ---- TRUE (FALL 2010 MIDTERM)
h. False? - the fruitfly need a PER:TIM dimer to inhibit clock rythms
lecture Oct 10, slide 36/39 - says working period gene is required for overt
expression of rhythmicity .... so yeah false... I think
k. False (?) because melatonin synthesis is inhibited by light, so it would be
produced based on the LD cycle, not the activity pattern of the animal
sounds right to me, were assuming it remains the same, and then the animals use
this cue differently?
... yes, I just googled this to confirm that nocturnal animals are active during the
melatonin peak: http://www.sleepdex.org/melatonin.htm
19. How do “night break” experiments indicate that a circadian oscillator
underlies photoperiodic time measurement? (5 points)
Night breaks which occur 24 hours after a light interval (day) are able to
disrupt photoperiodic time measurement.
when light falls during an organisms subjective night, they respond as if on a
two examples of plant on “night break” schedules. The short day plant flowers
on the short photoperiod, but flowing is stopped if there is a short pulse of light at night. The long day plant responds in the opposite way.
i thought night breaks have random light pulses and resonance has a
scheduled light pulse
20. In mid spring in the N. Hemisphere, starlings are trained to find food at
9AM (in the SE corner) of an outdoor arena. Assuming they use their circadian
clock and the location of the sun. (12 points)
a) In what direction are they predicted to search at noon the next day?
b) In what direction would these birds search at noon, if the sun is hidden, and
an image of the sun is provided by a mirror to the north?
c) If after training, these birds are put in constant conditions, then tested three
days later at 9am in what direction will they search assuming their circadian
periods average 24hrs?
d) In what direction will the animals in (c) search, if their circadian periods
average 25 hrs?
e) If after training, these birds are ent