A Mnemonic for the Krebs Cycle Using Letter Additions, Letter Deletions, and Anagrams To Trace the Acylation, Decarboxylations, and Other Changes John P. Williams
Miami University-Hamilton, Hamilton, OH 45011 The Krebs (citric acid) cycle is a cornerstone of the study of metabolism. Confirmation of its importance comes from Hans Krebs who shared the 1953 Nobel prize in medicine and physiology for his work on this process. The net structural effect of one complete turn of the cycle is simply the conversion of a 2-carbon species (acetyl) to two molecules of carbon dioxide. (The resulting energy produces ATP.) However. when first learnim the steowise reoresentation of the krebs cycle, students generacy miss &is essential conceot due to the comolexitv of the individual structures, and often t h e b o f u & o n of accompanying information. This paper describes a nonchemical mnemonic that promotes a student's insight into the Krebs cycle. By highlighting a series of simple progressive changes in a ring of simple familiar words, students more readily comprehend the 1-or 2-carbon structural differences between each reactant and product. The Mnemonic
Getting Rid of Some Four-Letter Words
A 4letter word no longer means what it used to mean!
I2 Adding 2 Letters Shows the Addition of 2 CAtoms: Acylation
The mnemonic shown by Figures 1and 2 begins with the acylation of oxaloacetate to citrate. Two carbons (acetyl) are added to a lcarbon species (oxaloacetate), forming a 6-carbon species (citrate). This is shown as the addition of 2 letters to a 4-letter word to form a &letter word. oxaloacetate + aeetyl group + citrate 4 carbons + 2 carbans + 6 carbons sing + le + single Using Anagrams when the Chain Length is Static A New Letter Indicates a New Molecule In a common version of an anagram game, participants generate a series of recognizable words by making l-letter changes in a previous word (e.g., band to bald to bold to hold). In this mnemonic such changes represent reactions in which no carbons are gained or lost. After the acylation to a 6-carbon species, this chain length remains the same in the next three reactions. For example,
A Letter is a Carbon Atom I2 A Word is a Molecule
So a 4-letter word is really just a molecule with four carbon atoms.
m- Pc-u 1
d1 P w
' R cn-c-w 1
Figure 1. Amnemonic using letter additions, letter deletions, and anagrams in cycle format.The changes in letters are indicated by highlighting.
F~g~re 2 Krebs cycle show ng the srr~cl~ral form~lasof eacn spectes. The changes in atoms ano oonds are shown by n~ghigntmg. Volume 69 Number 12 December 1992
Showing the Loss of the Carbon Dioxide
* A Dropped Letter Indicates the Loss ofa Carbon: Decarboxylation One carbon is lost (as carbon dioxide) in each of the next two reactions. forming a 5-carbon and then a 4carbon suecies. For example, a-ketoglutarate - carboxyl group + succinate 1carbon + 4 carbons 5 carbons g + mane mange After three further reactions, the initial 4-carbon oxaloacetate species is regenerated. Summary
An acylation,that is, addition of a 2-carbon spedea (adding2 letters to a bletter word to form a 6-letter word) Three chanees that do not affect chain leneth !three l-let;& changes to keep a 6-lettrr &d T w o decnrhoxylations( t w o l-letter drlcrinns