TRAVELLER Energy
ORIGIN Your lunch
DESTINATION Your cells
DURATION Hours
A typical sandwich contains billions upon billions of buzzing electrons. The bonds they form hold together the sugar, carbohydrate, fat and protein we call lunch. The energy in those bonds will eventually power your body, but it can do you no good locked in a sandwich. Luckily, electrons have you covered.
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Our electron鈥檚 journey begins with a bite. Attached to a starch molecule, it is pushed from your mouth to your stomach and then small intestine. Its starchy home is torn asunder by enzymes from the pancreas, and now our intrepid electron is adrift on a molecule of glucose.
It crosses into the bloodstream, passing briefly through the liver, to join the rush of cells, chemicals and plasma that complete a circuit around the body roughly every minute. Before too long it finds its way into a muscle cell.
The interior of a cell is far from safe. The electron鈥檚 glucose raft is quickly cut into pieces by a 10-step chemical disassembly line. Hanging on to one of the pieces, our electron is now headed for the cell鈥檚 power plant: the mitochondrion. This is where the electron鈥檚 energy truly comes into its own. Inside, it will enter the final stage of its journey: a series of reactions known as the electron transport chain.
Like a boulder perched at the top of a hill, with a bit of a nudge, the electron tumbles from higher energy states to lower, releasing energy along the way. Enzymes manage the fall, stair-stepping the electron to ever-lower states.
鈥淟ike a boulder perched on top of a hill, with a nudge the electron tumbles, releasing energy as it goes鈥�
Energy released at each step is used to drive a pump. Protons are pushed, one by one, across a membrane in the mitochondrion and pile up on the far side. Like fans desperate to get inside a stadium, the protons have a single drive 鈥� to get back through the membrane. As they push through molecular turnstiles, the energy they release glues a phosphate to an ADP molecule: adenosine diphosphate is turned into adenosine triphosphate. You may have heard of it as ATP. This is the cell鈥檚 ultimate source of energy.
By the time the electron has bumped its way down to the end of the chain, some 32 ATP molecules have been made. Drained, our electron joins forces with a leftover proton, and two of these hitch themselves to an oxygen to form water. Flushed out of the cell, the water molecule makes its way to the lungs and moistens your breath.
But the electron鈥檚 energy lives on, in the form of ATP. When, a few hours after lunch, you stub your toe, it helps activate a muscle cell contracting the diaphragm. This expels carbon dioxide and our electron鈥檚 water molecule out of your lungs. The molecule shoots past your voicebox and out into the world as a cry of pain.
Read more about your billion-year history in these seven fantastic journeys of the stuff that makes you
(Image: Adie Bush/Getty)
This article appeared in print under the headline 鈥淔rom a sandwich to a scream鈥�
