Chapter 10 - Circadian rhythms and biological clocks

Question 1

Chronobiology

Answer 1

The scientific discipline that examines biological rhythms

Question 2

Circadian rhythm

Answer 2

A rhythm of a biological phenomenon, driven by an endogenous time-keeping system, with a period close, but not equal, to 24 hours

Question 3

Eclosion behavior

Answer 3

• Emergence of adult insects from the pupal cases or of larvae from the eggs
• The insects are very vulnerable after emerging, so this occurs extremely early in the morning when the sun is not yet powerful
• Drosophila do this

Question 4

Entrainment

Answer 4

The circadian rhythm of a biological clock can be synchronized to the 24h cycle of the environment by the process of entrainment

Question 5

Zeitgebers

Answer 5

Entraining cues

Question 6

Actogram

Answer 6

Plot of the recorded activity of an individual during a given time period

Question 7

Mutagenesis

Answer 7

The process by which a mutation occurs in nature, or is induced in the laboratory using mutagens (e.g., X-rays, UV light, specific chemicals)

Question 8

Clock mutant flies

Answer 8

• In all three mutant fruit flies exhibiting eclosion rhythms different from wild-type flies (arrhythmic, short-period, and long-period), the same gene of the X chromosome is affected
• This gene is called period or per

Question 9

First two clock genes discovered and cloned

Answer 9

• Period (per)
• Timeless (tim)
• Each of these genes is an essential component of the drosophila clock system
  – Null mutations in either of the two genes render the flies arrhythmic

Question 10

Null mutation

Answer 10

Any mutation of a gene that results in a lack of function

Question 11

Relative abundance of per RNA extracted from the head tissue of drosophila

Answer 11

See diagram

Question 12

Suprachiasmatic nucleus (SCN)

Answer 12

• A paired neuronal structure in the brain, at the base of the hypothalamus, just above the optic chiasm
• It receives photic input from the retina via the optic nerve
• Plays an important tole in the regulation of the body’s circadian rhythms

Question 13

Melatonin

Answer 13

• A hormone secreted by the pineal gland in the brain and by some other organs, including the retina
• Its circulating levels exhibit daily cycles

Question 14

Luciferases

Answer 14

• Enzymes that catalyze the oxidation of luciferins to produce light in a bioluminescent reaction
• The best-known luciferase is that produced by the North American firefly, which emits green light
• Luciferase (luc) genes can be inserted into the DNA of other organisms so that the light produced acts as a ‘reporter’ for the activity of regulatory elements that control the expression of luc