studyguide Flashcards
(20 cards)
What are circadian clocks, and why are they important for cyanobacteria?
Circadian clocks are internal timekeeping systems that help organisms anticipate and adapt to regular changes in the environment, like the day-night cycle. In cyanobacteria, they optimize metabolic processes like photosynthesis.
Who are the key protein components of the cyanobacterial circadian clock?
KaiA, KaiB, and KaiC.
What is the KaiABC In Vitro Oscillator (IVO)?
An experimental system where purified KaiA, KaiB, and KaiC proteins are mixed with ATP to reconstitute the oscillatory phosphorylation of KaiC outside of living cells.
What does each Kai protein do in the oscillator?
KaiC: Core component with autokinase and ATPase activity; KaiA: Enhances KaiC phosphorylation; KaiB: Facilitates KaiC dephosphorylation and sequesters KaiA.
What are the main insights gained from IVO experiments?
The KaiC phosphorylation cycle can sustain oscillations without transcription-translation feedback loops, proving that a protein-only oscillator can function.
What is the Expanded In Vitro Clock (IVC)?
A more complex in vitro system that includes clock output and input proteins like SasA, CikA, and RpaA to better mimic in vivo conditions.
What environmental cue resets the KaiABC clock?
Changes in the ATP:ADP ratio.
What role does SasA play in the clock system?
SasA is a histidine kinase that interacts with KaiC to help transmit circadian timing information to downstream components.
What role does CikA play in the clock system?
CikA helps reset the clock by promoting dephosphorylation of RpaA and responding to environmental changes.
What is temperature compensation in circadian clocks?
The ability of the circadian clock to maintain a consistent period across a range of physiological temperatures.
How might KaiA, KaiB, and KaiC interactions support temperature compensation?
Through cooperative dynamics that stabilize KaiC’s ATPase activity despite temperature fluctuations.
What is the difference between an hourglass timer and a circadian oscillator?
Hourglass timers need regular environmental cues to reset, while circadian oscillators maintain rhythmic activity autonomously.
How does Rhodobacter sphaeroides’ KaiBC system differ from the S. elongatus KaiABC system?
It functions as an hourglass timer, not a self-sustained oscillator, and responds directly to ATP:ADP changes without KaiA.
What is the significance of the KaiCRs dodecamer structure?
The dodecamer formed via a coiled-coil domain suggests unique structural properties that may relate to its timing function.
Why is understanding KaiC ATPase activity important?
It is central to circadian timing and temperature compensation; understanding it could reveal fundamental principles of biological clocks.
How can IVC systems be used to study clock output?
By including reporter DNA and output proteins like RpaA, researchers can observe how the clock influences gene expression.
What methods are used to measure KaiC phosphorylation?
SDS-PAGE to separate phosphorylated from unphosphorylated forms.
What method is used to quantify ATPase activity in KaiC?
HPLC (High-Performance Liquid Chromatography) is commonly used to measure ADP production.
Why is magnesium important in the KaiC system?
It may act as a co-factor or regulatory ion influencing KaiC activity and stability.
What is metabolic compensation in circadian clocks?
The ability of the clock to buffer against fluctuations in metabolic conditions (e.g., ATP:ADP ratio) to maintain accurate timing.
