Integrated SequencePhysics Chemistry Organic Biology

Web Resources

  click if a link is broken

Special points of emphasis


Nucleic Acids

Gene Expression

Supercoiled DNA is more compact. With circular DNA, a superhelix is not simply the circular DNA strand in twisted conformation. The superhelix is a topoisomer of the circular DNA where all base pairs are in place. Topoisomers are topological isomers, molecules with the same chemical formula but different topologies. Topoisomers can only be interconverted by breaking and reforming bonds. Topoisomerases are enzymes that carry out this interconversion. Imagine trying to untangle a phone cord if it were a complete circle. You couldn't do it without cutting it. DNA gyrase is a topoisomerase that moves in the other direction. It consumes ATP to impart the free energy of supercoiling to DNA. DNA gyrase and topoisomerase 1 are antagonists.

The WikiPremed MCAT Course is a free comprehensive course in the undergraduate level general sciences. Undergraduate level physics, chemistry, organic chemistry and biology are presented by this course as a unified whole within a spiraling curriculum.

Please read our policies on privacy and shipping & returns.  Contact Us.
MCAT is a registered trademark of the Association of American Medical Colleges, which does not endorse the WikiPremed Course.

Creative Commons License
The work of WikiPremed is published under a Creative Commons Attribution Share Alike 3.0 License. There are elements of work here, such as a subset of the images in the archive from WikiPedia, that originated as GNU General Public License works, so take care to follow the unique stipulations of that license in printed reproductions. You can use the resources here for commercial or non-commercial purposes, but please give attribution and a link to the production credits and edit history of the resource. For the works here which began as my individual work, please attribute "John Wetzel, an author at".