Brain BREAK! presents: ATP & ADP
Note: Learning about ATP for the first time was frustrating. For class, I only needed to know the acronym, it was something the body used for energy, it was important, and ADP was also a thing. This did not satisfy me. I couldn’t understand. I spent at least an extra hour of study time looking at the chemical structure of ADP, making flashcards of the molecules, and really putting my nose to the grindstone to grasp the whole picture. I didn’t have to know for class, but I had to know for myself. Some topics are like that. Going a little beyond the curriculum can help the subject really “click.” If this describes you and ATP, read on!
Adenosine triphosphate. ATP. What is it? In chemical terms, it’s made up of adenine, a.k.a. two nitrogen-happy rings; one ribose, a.k.a. sugar; and three bundles of Ps and Os called phosphate groups. Adenine + ribose = adenosine. “Tri-” means three, so triphosphate. Adenosine triphosphate.
We can simplify this into something more accurate: a power source! Think of a plain old double-A battery. ATP is a battery that stores the energy to power your remote control – or an active transport channel in a cell membrane. When this third phosphate group is kicked off in some bodily function– zap! – that’s a catabolic process. As we know from Chemistry 101, a catabolic process disperses energy. Thus, ATP is a power source by the action of its third phosphate group being separated in a flash.
When this zap of energy has been used up, we’re left with adenosine diphosphate, or ADP. The “di-” means that there are only two phosphate groups on the molecule. Think of ADP as the battery casing. If ATP is a full battery, ADP is a drained battery. Meanwhile, the lone phosphate group is floating around like Darth Vader in his topsy-turvy TIE fighter at the end of Star Wars. (“Whooooh-pehhhh, whooooh-pehhh!”)
This is usually where we stop. But am I done? Nope. Your body has its own charging stations. After all, we don’t throw away all that phosphate. That would be enormously wasteful. (And imagine peeing or sweating phosphorus. They say it smells like matches and garlic. Gross.) Inside the folds of mitochondria – the powerhouse of the cell – there are little doodads called ATP synthase. “Synth-“ meaning to make, and “-ase” letting us know that it’s an enzyme. Translated, it’s an enzyme that assembles ATP. Its job is to take ADP, add a free-floating phosphate group, and bam, we have ATP – a charged battery that can go out into the cell and do the heavy lifting. What’s great about this system is that ATP synthase uses protons for its power, so it doesn’t need ATP to work. (It wouldn’t make a lot of sense to use ATP to make an equal amount of ATP.) And that’s ultimately how you “get” ATP from the electron transport chain.
There you have it. ATP doesn’t ride in on a unicorn and magically make energy. It is really all about this cycle of energy ready, energy released, energy replaced – and it’s always going on. Isn’t it nice how environmentally responsible your body is? Really, good job. LEED certification is in the mail.
With all this, you’re probably wondering what adenosine monophosphate might do. Well, fun fact. It’s in your DNA… it’s a nucleotide! The one (mono-) phosphate group and ribose form the “backbone” of DNA, and adenine is one of your four main bases in genetic code (A, T, G, C). One rung of the DNA ladder would be adenosine monophosphate paired up with thymidine monophosphate. Isn’t it kind of weird to think that a couple of little phosphorus atoms make all the difference between a how your muscles move and how your hair color is determined? And then what about adenosine tetraphosphate? Why not keep going? Well, tetraphosphate can be broken down by one of the enzymes involved in cellular respiration, too. Pretty neat stuff.
“Where’s the ATP?”
“Use the one in the remote!”
-CNx