The chain elongation reactions catalyzed by DNA or RNA polymerases are nucleophilic addition-elimination reactions similar to the acyl substitution reactions among carboxylic acid derivatives but occurring here upon the innermost phosphate group of a deoxyribonucleoside triphosphate instead of a carbonyl group. Picture deoxyribonucleoside triphosphate in your mind. The nucloephile is the 3' -OH terminus of the primer. Thermodynamically, the synthesis is driven forward by the hydrolysis of pyrophosphate.

The other major announced change with the new 2007 MCAT, aside from the somewhat shorter, computerized format, will be an increased emphasis on genetics and molecular biology. A major part of the challenge in preparing will be to work on your vocabulary and comprehension skills for passages in this area. In the above passage, were you comfortable reading 'deoxyribonucleoside triphosphate' or even more importantly, '-OH terminus of the primer'?

The WikiPremed MCAT Course is a 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. WikiPremed offers the customers of our publications or our teaching services no guarantees regarding eventual performance on the MCAT.

Creative Commons License
WikiPremed is a trademark of Wisebridge Learning Systems LLC. The work of WikiPremed is published under a Creative Commons Attribution NonCommercial ShareAlike 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.