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Biology 404 > Circadian Rhythm > Flashcards

Circadian Rhythm Flashcards

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1
Q

Define circadian rhythm

A

Sustained oscillations with a period of approximately (but not exactly) 24 hours

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2
Q

What kinds of organisms have a circadian rhythm?

A

All! Everything from bacteria to mammals to plants

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3
Q

Why is circadian rhythm important?

A

Allows an organism to be more productive in its waking hours: e.g. do not want to be sleepy and hungry at the same time, if they are staggered we can take care of ourselves better

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4
Q

What are the 3 components of the biological clock?

A
  1. Input: a way to set the clock
  2. Oscillator: the clock itself
  3. Machinery: Helps allow the clock to control the activity of genes which need to be regulated
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5
Q

How were genes associated with circadian rhythm discovered in D. melanogaster?

A

Monitored eclosion (emergence of adult from pupa stage) and did genetic screening of adults which emerged at the “wrong” time (it is normally supposed to happen in the morning)

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6
Q

The SCN is part of this brain structure

A

The hypothalamus

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7
Q

The “oscillator” in human/mammal circadian rhythm is…

A

The SCN

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8
Q

Cells from this region in vitro can maintain 100% of their circadian rhythm

A

SCN neurons

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9
Q

What is the role of the SCN?

A

Send output to peripheral tissues to follow the body’s CR due to light cues

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10
Q

When a non-SCN cell is in isolation, what happens to its CR?

A

Maintain their rhythmicity given the medium is changed periodically, but the intrinsic rhythm does not respond to light cues

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11
Q

What TFs make up a heterodimer and bind to the Ebox element upstream of important circadian rhythm genes?

A

Clock and Bmal1

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12
Q

The Clock/Bmal1 heterodimer promotes the transcription of these genes (3)

A
  1. Period (Per)
  2. Cryptochrome
  3. Rev-erb alpha
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13
Q

Which is thought to be the most “important” of REV, Per, and Cry?

A

Per

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14
Q

How can expression of Bmal1 be inhibited?

A

REV acts on the DNA regulatory region for Bmal1 = negative feedback

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15
Q

Which complex inhibits the Clock/Bmal1 dimer?

A

Per/Cry complex

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16
Q

How is expression of Clock/Bmal1 reinitiated after inhibition by Per/Cry?

A

With Per/cry inhibition, Clock/bmal1 stop acting on their target genes, Less REV/Per/Cry activity, therefore there is less REV inhibiting clock and Bmal1 and less Per/Cry to inhibit the clock/bmal1 complex

17
Q

The SCN has direct connections to this hormone-secreting gland which affects the sleep/wake cycle

A

The pineal gland

18
Q

What is the main secretion of the pineal gland?

A

Melatonin

19
Q

Melatonin is derived from…

A

Tryptophan

20
Q

At what time of day is melatonin upregulated?

A

Night

21
Q

To improve jet lag, when should one take melatonin during travel?

A

At the destination’s “dark” time

22
Q

How is the circadian clock reset?

A

Light input coming from the retina to the SCN

23
Q

The connection between the retina and the SCN is called the…

A

Retinal hypothalamic tract

24
Q

The resetting of the oscillator by light is called…

A

Photoentrainment

25
Q

During an assessment of locomotor activity, when mice with functional eyes (no enucleation) are put in several days of darkness, what happens to their CR?

A

Maintains rhythmicity but starts to become “skewed” - because rhythm is not quite 24h

26
Q

The mouse circadian rhythm is (more/less) than 24h

A

Less

27
Q

The human circadian rhythm is (more/less) than 24h

A

More

28
Q

What is the primary function of ipRGCs?

A

Responsible for photoentrainment, project to SCN via retinohypothalamic tract

29
Q

Describe the circadian rhythmicity of rd/rd mice. Why is it like this?

A

More or less the same as wt mice: because these mice still have ipRGCs

30
Q

How can you get an rd/rd mouse to stop responding to circadian light cues?

A

Enucleation (removal of the eye :( )

31
Q

When mice are enucleated, what are the 2 results?

A
  1. Loss of photoentrainment
  2. Loss of pupillary reflex
32
Q

NMDA channels open in response to…

A

Glutamate

33
Q

How are circadian clock genes activated?

A

Ganglion cells signal to target cells by releasing glutamate, which binds to NMDA channels causing them to open. Ca2+ enters the cell and activates CREB, which activates circadian clock genes (particularly Period)

34
Q

Period is at its highest at (dawn/dusk) in mice

A

Dusk

35
Q

A burst of light at dusk will (advance/delay) circadian activities

A

Delay

36
Q

A burst of light at dawn will (advance/delay) circadian activities

A

Advance

Biology 404 (14 decks)

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