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Super Helix
Name: Finoe
Status: Student
Grade: Other
Location: N/A
Country: Hong Kong
Date: November 2008
Question:
My textbook stated that the DNA helix if further coiled to
produce a super helix. I would like to ask that what is a super helix
Replies:
Imagine that a piece of yarn is a DNA double helix. Look at the yarn closely
-- see how there are smaller strands wrapped around each other? This is a
little like a DNA double-helix. Now take the ends of the yarn and twist them
(keep twisting!). After a few turns, the yard will start to coil up on
itself. Keep twisting and the yard will keep turning on itself more. This is
a supercoil.
Here's an electron micrograph (a special kind of imaging) of supercoiled
DNA:
http://cmgm.stanford.edu/biochem201/Slides/DNA%20Topology/072%20Supercoiled%
20DNA%20jpeg.JPG
Hope this helps,
Burr
I take your book actually said " The DNA helix is further coiled to produce a
super helix "
while I am not familiar with the term superhelix, I am familiar with the
structure of DNA.
If you take a piece of string and twist it, the fibers within the string
take on the form of a helix - (Some people call this an elongate spiral,
although technically a spiral is a flat widening curve like a nautilus shell)
If you continue to twist the string WITHOUT TENSION it will curl on itself
and form a loop with a double twist. That is a similar structure to the
superhelix form of DNA. There are twists within the twists, within the
twists. Try it with your telephone cord if you have a half hour to spare
untangling it afterward.
Nor is this structure exclusive to DNA - many proteins are similarly twisted,
and that is one of the reasons why many proteins are flexible molecules, and
why they can be so easily damaged by heat. When you cook an egg, you cause
the twisted helical molecules of the albumen - which are normally springy and
elastic, to become tangled and knotted. I often have kids think of a tangled
slinky spring - the coils getting caught on each other, until you get a rigid
mess - analogous to a hard boiled egg.
Nigel Skelton
Tennant Creek High School
AUSTRALIA
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