Circadian Rhythms Flashcards
What is a circadian rhythm?
A biological process which has a period of about 24 hours. It continues in the absence of external stimuli and is temperature compensated (buffered to temperature change)
What is a circadian oscillator?
Generates a rhythm with an appropriate 24 hour period within the cell
What is an entrainment pathway?
Synchronises the oscillator with the external time of day so the clock stays accurate
Output pathways
Communicate temporal information from the oscillator to other parts of the cell
Circadian gating
Adjusts the sensitivity of entrainment and output pathways depending on the time of day
What are most circadian clocks?
Transcription-translation feedback loop
The protein encoded by gene A activated gene B
The protein encoded by gene B represses gene A
Where is the mammalian circadian clock?
Within the brain - there are ‘pacemaker’ cells
What carries out the synchronisation of the circadian clock with the environment?
Zeitgebers (time givers)
What receptors detect red and blue light in plants?
Phytochrome - red
Cryptochrome - blue
What environmental signals provide information to oscillators?
Feeding in mammals and insects Light detection in plants Sugars from photosynthesis in plants Temperature fluctuations Centralised to the eye, retinohypothalamic tract and suprachiasmatic nucleus in pineal gland in mammals
What percentage if plant gene transcripts have a circadian rhythm?
6-30%
What does the pineal gland release at night?
Melatonin
What is released from the adrenal gland during the day?
Cortisol - causes energy release and fat burn
