Circadian%20Rhythms:%20Lecture%205

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Circadian Rhythms Lecture 5 The Plot Thickens...
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What makes the clock tick? Hands of the SCN
Main Oscillator (SCN cells) But what about at
the molecular level? GENES (contain the
instructions that tells a cell what its job will
be)
Cells contain a newly discovered protein (clock
protein) that regulates gene function and which
shows 24-hr variations in cellular levels that
appears to account for 24-hr variations in
neuronal activity
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• Genes that underlie our Biological Clock
• How do reseachers study this?
• How do you begin studying genes
• Simple Model
• Short-life span (inherited mutations)

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Drosophila (Fruit Fly) Ideal for Genetic
Studies 1. Short Life Span breed interbreed
1,000s of generations 2. Size of fly is Small
Lab set up minimal!
Genotype gene Phenotype
outward behavior attributed
to function of the gene
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So..We want to know if there is a particular
gene (genotype) responsible for circadian rhythms
(phenotype)
Start backwards ? we dont know the gene but we
do know the behavior ? disruption in circadian
rhythms
We need to measure circadian rhythms in
Drosophila Active during the day 12L/12D
cycle
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Measurement of Activity in the Fruit FLy
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Get the phenotype disruption in 12L/12D Cycle
Mutant Genotype
Konopka Benzer (1970)
1. Fed the flies mutagens
29 hr cycle
2. 2,000 of their progeny (200th try)
No cycle
19 hr cycle
3. Found 3 flies showing disrupted 12L/12D
cycles ..first to tie behavior to gene (Period)
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16 years later Michael Young (1986)
Found that 3 flies had alterations in a single
gene
X Chromosome

• Period PER
• PER is somehow involved in
• producing circadian rhythm
• setting the length of the rhythm

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Is this the only gene involved?
Start from the drawing board
Fed flies mutagen
7,000 Progeny ONE Fly!..had no circadian rhythm
Mutation on Chromosome 2 Named it TIMELESS
TIM. So do these two genes work together?
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Genes are made of DNA- located on Chromosome
DNA instructions for making proteins
(AT GC) DNA never leaves the
cell Instructions are copied onto RNA mRNA
(transcription) mRNA leaves nucleus enters the
cytoplasm with the molecular recipe for amino
acids Rough ER (ribosomes) translation
amino acids

proteins
DNA
mRNA
ER-ribosomes
nucleus
Cell body
PER/TIM Proteins
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Do PER TIM work together?
So, isolated both PER TIM (genes)
PER Protein TIM Protein
PER
TIM
Put them together
stuck together
HEY DUDE ..they must interact with each other
inside the cell!
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After many experiments
Discovered a clock-like loop
PER TIM genes are active until their proteins
begin to bind to each other (heterodimer)
They form complexes that enter the nucleus shut
down their own genes (with the help of Clock
Cycle)
After a few hours - enzymes degrade the
complexes Viola..the cycle begins again!
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FANTASTIC WEBSITE!!!!!
http//learn.genetics.utah.edu/features/clockgenes
/
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Sothe SCN now known as one of the main
biological Clockshowever now we know that genes
are involved also .These genes have recently
been identified in humans and rodents!
Across the tree of life, from bacteria to humans,
clocks use oscillating levels of proteins in
feedback loops to keep time. Perhaps more
amazing, fruit flies and mice separated by
nearly 700 million years of evolution share the
very same timekeeping proteins. "First Runner
Up A Remarkable Year for Clocks," Science, 1998.

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Biological Events Linked to Certain times in the
24 hour cycle
100 am Pregnant women are most likely to go
into labor 200 am Levels of growth hormone are
highest 400 am Asthma attacks are most likely
to occur 600 am onset of menstruation is most
likely to occur - Insulin levels lowest
- BP HR begin to rise 700 am
Hayfever symptoms hi 800 am Risk for
heart attack stroke
highest 600 pm urinary flow is
highest 900 pm pain threshold
lowest 1100 allergic responses most
likely