Circadian rhythms and sleep

Question 1

Circadian clock

Answer 1

Endogenous molecular pacemaker

Daily oscillations

Question 2

Core molecular clock

Answer 2

subset of evolutionarily conserved genes that drive oscillations

Question 3

Free run

Answer 3

biological rhythm exists without external input or cues.

Question 4

Entrainment

Answer 4

Biological rhythm synchronised to external (light/dark) oscillation

Allows adaptation to different lengths of day (seasons)

Question 5

Period clock mutants

Answer 5

per0 mutant alleles produce arrhythmicity
PerL produced long period rhythms
PerS produced short period rhythms

Question 6

Circadian rhythm properties

Answer 6

Oscillations persist under constant conditions
Events recur approximately every 24 hours
Rhythms entrained by changes in light and temperature
Period of clock is stable over a wide temperature range

Question 7

Parts of the circadian system

Answer 7

Core clock keeps time
Input pathways synchronise clock to environment
Output pathways transmit information to organise behaviour

Question 8

Core clock negative feedback loop

Answer 8

Clock/Cycle protein complex binds E-box in promotor of period and timeless genes
PER and TIM proteins modified by doubletime and phosphatases
PER/TIM dimerise, move to nucleus and repress CLK/CYC
Can bind SLIMB(E3) for proteolysis

Question 9

Zeitgebers

Answer 9

Harmonise clock neurons to the environment

Light, temperature, social cues

Question 10

Light

Answer 10

Reaches clock neurons via rhodopsin-containing photoreceptive organs

Activates crytptochrome. Cry recruits Jetlag which ubiquitinates Tim for degradation

Jet ubiquitinates Cry in absence of Tim

Question 11

PDF neurons

Answer 11

Output transmitter of clock
act as internal zeitgeber
Phase neuron oscillations to right time of day
Light-input and arousal factor of clock

Question 12

Morning activity

Answer 12

Promoted by s-LNvs and DN1s

Question 13

Evening activity

Answer 13

Promoted by LNds and fifth PDF-negative s-LNv

DN1s but very weak in high light

Question 14

Sleep regulation

Answer 14

Circadian regulation is timing of sleep (preferred bedtime)

Homeostatic increases drive to sleep the more time spent awake

Question 15

SLEEPLESS

Answer 15

Identified via forward genetic screen
Required for sleep in Drosophila
Signalling molecule that connects sleep drive to lowered membrane excitability
Loss leads to 80% reduction in sleep