Circadian Rhythms

Question 1

How long is the average circadian period of the human internal clock?

Answer 1

24.18 hours

Question 2

What is known as ‘The Master Clock’?

Answer 2

Superchiasmatic nucleus, all other molecular clocks in peripheral tissues are hierarchically influenced by this nucleus.

Question 3

Where is the superchiasmatic nucleus located?

Answer 3

Under the hypothalamus. It has 2 parts, each with about 20,000 neurons.

Question 4

What 3 mutations were identified in the fruit fly that affected it’s circadian period and where were they all located?

Answer 4

Shorten, apolish and lengthen and they were all located on the same locus in the same gene (the period gene)

Question 5

Describe the Clock, Bmal, Cry and Per feedback loop.

Answer 5

Clock and Bmal1 form a heterodimer, which is a transcription factor in the nucleus, and transcribe Per and Cry. Per and Cry then move to the cytoplasm where they are translated and phosphorylated. When a critical level of these molecules is produced they return to the nucleus and inhibit Clock and Bmal which in turn inhibits their own production. This causes an oscillatory behavior.

Question 6

Is the SCN the only clock in the body?

Answer 6

The there is clocks in all major organs, tissues and cells in the body.

Question 7

Are only the core clock genes required for the oscillation of circadian gene expression?

Answer 7

No. It is not only about the core clock genes it is also about the underlying epigenes. When exon 19 is deleted then histone methyltransferase MLL1 cannot bind to the Bmal/Clock heterodimer and leads to a nonactive transcription.

Question 8

Define chronotype

Answer 8

Phase of entrainment

Question 9

What 3 things can affect ones chronotype

Answer 9

Genetic predisposition, age and light exposure

Question 10

What is social jetlag?

Answer 10

The misalignment of biological and social time.

Question 11

Other than a survey what is another method to investigate ones internal circadian time? Name an advantage and disadvantage of this method?

Answer 11

A blood sample.
Take a blood sample and separate out the cells. Find the cells that oscillate and then investigate the transcriptome of the known oscillating cells.

Advantage: More accurate than a survey
Disadvantage: invasive, requires medical personnel and is expensive.

Question 12

Living against your intrinsic body clock leads to a decrease in the consumption of stimulants.

Answer 12

False. It leads to an increase in the consumption of stimulants.