firmasite-theme-enhancer domain was triggered too early. This is usually an indicator for some code in the plugin or theme running too early. Translations should be loaded at the init action or later. Please see Debugging in WordPress for more information. (This message was added in version 6.7.0.) in /home/rbrucep/public_html/tBioWordPress/wp-includes/functions.php on line 6121firmasite domain was triggered too early. This is usually an indicator for some code in the plugin or theme running too early. Translations should be loaded at the init action or later. Please see Debugging in WordPress for more information. (This message was added in version 6.7.0.) in /home/rbrucep/public_html/tBioWordPress/wp-includes/functions.php on line 6121Every Intro Bio student can cite ATP as ‘the energy currency of the cell’… but what do we mean by that? And why does it play that role? These are important questions, and they deserve answers. And real ones, not invocation of the mystical ‘high energy bonds’.<\/p>\n
Perusing Wiki for an image to link for ATP, I’m surprised to find how many directly imply that the ‘value’ is in the bond between two phosphates. I think suggesting that this is the case does a disservice to students’ ability to analyze and understand. We’ve taught them by now that bonds are simply shared pairs of electrons. Blaming the bond for the potential energy inevitably raises the question “Is it the electrons that are special? If not, what is it about the bond?”. No and nothing.<\/p>\n
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The funny thing is that if you project an image of ATP\u00a0with the charges correctly attributed to the phosphates<\/em> and simply ask the students ‘does this molecule look\u00a0happy<\/em> to you?’ [sometimes with follow on of ‘do all of those groups look like they’re comfortable next to each other?’] you can generally get a pretty raucous NO! It’s that simple. The phosphates don’t ‘want’ to be held in close apposition. Like charges repel, and these are glued in close proximity to one another.<\/p>\n All the phosphates want to be happy is to be set free from one another. And yep, it’s those pesky covalent\u00a0bonds<\/span> that stand in their way. The ‘high energy’ incorporated in the bonds is not about them; it’s about the difference between the presence of the bonds and their absence (this is a bit of sloppy shorthand in biology that Chemists have threatened me over; when a Chemist breaks a bond, they literally pull it apart and leave the halves unsatisfied. In biology, 99.9% of the time we’re actually talking about SUBSTITUTIONS–we\u00a0hydrolyze<\/em> ATP and essentially recombine a water with ATP to yield a phosphate and ADP… but no partial bonds or lone electrons). So our interest is in ‘before\/after’ comparisons, much like when we’re calling hydrogen bonds ‘weak’ because \u00a0the alternative to making an H-bond with X is… to make one with water, which is generally nearby.<\/p>\n Students can thus simply look<\/i> at ATP and directly ‘observe’ its potential energy–energy that can be converted to kinetic energy (a ‘fleeing’ phosphate) simply by setting a phosphate free. An upcoming post will cover a module on looking at an ATPase<\/a> as an easy to understand concrete example of a straightforward chemical reaction<\/a> enhanced by having a protein (enzyme) help out with the awkward parts. My lecture materials on ATP and walking through an ATPase as an explicit example of enzyme function can be found here<\/a>.<\/p>\n I generally leave ATP at this point for a while, but I think it’s critical to return once the focus of the course becomes energetics itself. A key question is WHY is ATP the ‘energy currency’? The simplicity of the chemistry above is a piece of the answer–any enzyme that can enhance the ‘popping off’ of the phosphate has access to that delightful burst of energy. And since water alone can trigger the event, it’s an easy one to assist.<\/p>\n