Lecture 19 Flashcards
Biological clocks
What do biological clocks provide to organisms?
Biological clocks give organisms intrinsic temporal (time) organization that is independent of changes in the environment.
What happens if an individual is isolated from the environment with no external time cues (e.g., mechanical clocks)?
Even in isolation, the individual will continue to exhibit regular cycles in all variables, maintaining internal rhythms.
What is meant by “synchronization” of biological clocks?
Synchronization refers to the alignment of cycles with external environmental cues. In isolation, biological clocks may continue to function, but they no longer synchronize with the outside world.
What is the definition of a “period” in biological rhythms?
A period in a rhythm refers to the amount of time between a particular part of a rhythm in one cycle and the same part of the next cycle.
What is a “circadian rhythm”?
A circadian rhythm is an endogenous rhythm with a period of about 24 hours. It continues without environmental cues but may not always persist in the absence of such cues.
What is the difference between rhythms that persist in the absence of environmental cues and those that do not?
Rhythms that continue without environmental cues are circadian rhythms, whereas those that don’t are not classified as circadian rhythms.
What is the role of environmental timing information in biological rhythms?
Environmental cues, such as light or temperature, help synchronize biological rhythms with the external world. Without these cues, biological clocks can still operate but may become desynchronized from external time.
How can the existence of an endogenous circadian rhythm be tested?
To test for an endogenous circadian rhythm, environmental timing cues need to be removed, and the organism’s rhythms should be monitored to see if they persist.
What does it mean for two rhythms to be “in phase”?
Two rhythms are said to be in phase if they occur synchronously, meaning they have the same timing or period.
What is a “circadian oscillator”?
A circadian oscillator is the mechanism that drives circadian rhythms, typically involving feedback loops of gene transcription that regulate the timing of these rhythms.
How do CLOCK and BMAL1 proteins contribute to the circadian clock?
CLOCK and BMAL1 are positive elements that drive the expression of genes like period and cryptochrome, which inhibit their own expression, forming part of the circadian feedback loop.
What happens when PER and CRY proteins accumulate during the day?
As PER and CRY proteins accumulate, they eventually enter the nucleus, block gene expression, and cause their own breakdown, completing the feedback loop that regulates the circadian rhythm.
Where are the biological clocks located in mammals?
In mammals, the biological clock is located in the suprachiasmatic nuclei (SCNs) of the hypothalamus, which are situated just behind the optic nerve.
How do genetic mutations affect circadian rhythms in animals?
Genetic mutations, like those found in mutant hamsters, can cause changes in the period length of their circadian cycles, such as making the cycle longer than normal.
