Molecular Motors

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Molecular Motors

• By Simone Siegel and Avery Baker
• (Dr. Shubeita)

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Molecular Motors

• Move lipid droplets
• Have two heads
• Walk along microtubules
• Take steps, like humans
• Study kinesin and dynein

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Kinesin vs. Dynein

• Well known
• Transports lipid droplets to positive end of
  nuclei
• Has a step size of 8nm

• Harder to study because of speed
• Transports lipid droplets to negative end of
  nuclei
• Has an unknown step size

http//bernstein.harvard.edu/research/motor_protei
n.htm
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Overall Goal slow down dynein and measure its
step size

• It is easier to see individual steps when dynein
  is slowed down
• Study at colder temps. In vivo (inside the cell)
• Reducing the temp. breaks ATP bonds less often,
  less energy released, should move slower

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Procedure fly embryos

• Learned fruit fly embryo preparation techniques
  (staging, peeling, mounting)

-Peel when about 2.5hrs old -nuclei are arranged
on outside of embryo -microtubules run to and
away from the nuclei -place on a flow cell, not
flattened so embryo doesnt know it is dead
http//www.nature.com/nature/journal/v414/n6864/fi
g_tab/414593a_F1.html
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Obtaining Data

• Record videos on cold DIC (Differential Interface
  Contrast) microscope

-you can see the lipid droplets moving -their
direction indicates whether kinesin or dynein is
moving them
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http//www.biologicalprocedures.com/bpo/arts/1/138
/m138.htm
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Analyzing

• With video, position of lipid droplets can be
  tracked
• Excel spreadsheet used to graph the data from the
  lipid droplet tracked
• Data shows the speed of the lipid droplet

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Graph of distance (nm) vs. time (sec)
-Plateaus indicate one or two dynein
molecules -Difficulty finding the velocity -Could
show dynein taking steps
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Graph of slopes of multiple lipid droplet tracks
-The y-axis is the velocity of the lipid
droplet -Several moved fairly slowly -Higher
speeds indicate that more dynein molecules were
moving the same lipid droplet -The cooler
temperature could have slowed down the speed of
movement
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http//www.bio.brandeis.edu/flyweb/