Molecular Genetics Flashcards
Circadian rhythm
has a period of about 24 hours
Continues in absence of
external stimuli
Is temperature compensated
Period
Time it takes for rhythm to complete a full cylce
Phase
The time at which a particular point of cycle occurs (peak)
Amplitude
The displacement of the oscillation from the centre point
Mimosa pudica plant
leaves open and close on a daily rhythm not reacting to light and dark
3 broad functions
Ensure responses to the environment are appropriate for the type of day
Co-ordinate timing of cellular processes
Measurement of the seasons
Circadian oscillator (clock)
Generate a rhythm with a 24 hour period within the cell
Transcription-translation feedback loops
Gene A produces a protein that activates Gene B
Gene B produces a protein that represses Gene A
Produces a cycle of gene expression - diff times of day - diff peaks of gene presence - 24 hour cycle
Reciprocal feedback loop
Negative feedback step
Speed of biochemical reactions adds a rate constant
Simple biological oscillator ^
Entrainment pathways
Synchronise the oscillator with the external time of day so that the clock stays accurate
Output pathways
Communicate temporal information from the oscillator to other parts of the cell
Circadian gating
Adjust the sensitivity of entrainment and output pathways depending on the time of day
Suprachiasmatic nucleus
area of the mammalian brain containing pacemaker cells - circadian clock
Plant vs Animal rhythm
Plant
Decentralised
each cell has its own rhythm and entrainment - can become slightly desynchronised
Animal
Centralised
Entrainment
The synchronisation of the circadian rhythm to the environment by zeitgebers (time givers)
Zeitgebers
Light
Temp fluctuations
Feeding
Sugars (plants from photo)
Output pathways
Communicate the estimate of time from the circadian oscillator to clock controlled physiology, metabolism, behaviour
Plant cell regulation by circadian clocks
circadian clock proteins - transcription factors
A transcription factor active during the day will activate certain genes but won’t activate them at night when it is not present (binds/doesn’t bind to promoters)
