Molecular Clockwork Flashcards
(13 cards)
1
Q
Clock gene
A
a gene whose protein product is necessary for the generation and regulation of circadian rhythms within individual cells throughout the organism
- mutations should affect the canonical clock
- amount or activity of the component must self-oscillate in a self-sustained manner with appropriate periodicity
2
Q
period
A
- mutations in Drosophila revealed period as the first circadian clock gene
- intracellular mRNA of period oscillates throughout the day
- different mutants have different periods of oscillation
- protein suppresses its own transcription
- negative feedback = oscillation
- rhythmic eclosion - time of Drosophila emergence is dictated by their circadian clock
3
Q
PER
A
- PAS sequence homology with Drosophila led to cloning of mammalian period
- PER proteins are members of PAS subfamily
- PER thought to have an autoinhibitory effect on their own transcription
- but cannot bind DNA alone!
3
Q
Per genes
A
- conserved between flies and mice
- oscillate with circadian period
- entrainable to light and reflect solar time
- needed for functional circadian rhythms
- critical for period or rhythm
- participate in autoinhibitory feedback loop
4
Q
CLOCK
A
circadian locomotor output cycles kaput
- clock gene identified by positional cloning
- functional identification of mouse CLOCK gene by transgenic rescue
- doesn’t need to oscillate as Per does, as has PAS domains
5
Q
BMAL1
A
component shown by yeast 2-hybrid studies
5
Q
CLOCK-BMAL1
A
- CLOCK and BMAL1 form a heterodimer
- acts as a transcription factor
- activates gene expression through Ebox sequences
5
Q
Cryptochrome genes
A
- in mammal, PERs bind CRYs
- CRYs encode promiscuous transcription repressors that form complexes with transcription factors such as PERs
- mice deficient in CRY1/2 are arrhythmic
5
Q
Drosophila CLOCK homology
A
- dCLOCK and cycle perform the same role in Drosophila
- bind Eboxes to promote transcription
5
Q
timeless (Drosophila)
A
- discovered by screen in Drosophila
- interacts with Per
- KO removes rhythmicity
- oscillates in phase with Per
- mammalian homolog has no role in circadian rhythm
- timeless does same thing as CRY but they are not related
5
Q
TTFL
A
transcription translation feedback loop
- for SCN circadian generation
6
Q
Extra SCN clocks
A
- tagging Per with luciferase means all cells show bioluminescent oscillations
- SCN may coordinate but TTFL rhythms are everywhere
- in culture, signal dampens due to destructive interference, but each individual cell is oscillating in a coordinated manner
7
Q
Proposed clock mechanism
A
- CLOCK and BMAL1 form heterodimer
- bind Eboxes to promote transcription of Cry1/2 and Per1/2
- CRY and PER interact
- CRY/PER inhibits CLOCK/BMAL1 promoting of CRY and PER transcription
