字幕表 動画を再生する 英語字幕をプリント Right now, trillions of chemical reactions are humming away in the cells of your body. You never feel them, but without these reactions, you wouldn't be alive. Unfortunately, each of those reactions needs some help. You see, most molecules are stable, they are happy just the way they are. The atoms in them are all bound-up and friendly with one another and would prefer to stay that way. The problem is, for a chemical reaction to happen, the atoms that make up those stable molecules need to break away from their friends and go buddy up with another atom. This break-up is where the molecules need a hand. This initial kick-start is known as activation energy. It's used to destabilize the molecule, to push the bonds between the atoms to a place where they are ready to break. This unstable state is known as the molecule's transition state. Once a transition state has been achieved, the atoms become willing to leave their current molecular friends and go make new friends elsewhere. Once they are convinced, it's a piece of cake. Bonds break, atoms rearrange, and the rest of the reaction happens automatically. After that first push, the body doesn't need to put in any more energy to help the reaction along. Left alone, most of these reactions would be very slow because it takes quite a while to build up the activation energy the molecules need to get started. Enter the enzyme. Enzymes are proteins that speed up, or catalyze, reactions by lowering the activation energy. They make it easier for the molecule, also known as a substrate, to get to the transition state. You can think of a reaction like a race. Some racers are running along, while others have teammates to help them. Meet Sam the Substrate. His team is the MODS Squad. Together, his team is able to get to the finish faster, using less energy. There are four special enzymes in Sam's team. Each has a different strategy for lowering the energy it takes to get going and speeding up the pace to get the MODS to the finish line. The "M" stands for "microenvironment". This enzyme creates a tiny, special environment for the substrate, resulting in a faster reaction time. He runs ahead of the pack, flattening out bumps in the road and misting cool water on his team of molecules. "O" is for "orientation". Sometimes two molecules must be positioned just right before they will react. Like a friend at the finish line, the O enzyme provides his molecules with specially shaped spaces that allow the substrates to interact in just the right way. "D" stands for "direct participation". Every now and again, a little muscle is needed. And when his teammates are struggling to finish the race, Teammate D is there to pick them up and carry them over the line. Finally, "S" is for "straining bonds". This guy pushes the team through some serious flexibility exercises: splits, lunges, backbends, the works. Sometimes his substrate teammates just need to be stressed and flexed into their transition state. So that's it. Remember that all reactions need energy to get going. This energy is known as the activation energy. Enzymes lower that activation energy and speed the reaction through team MODS: microenvironment, orientation, direct participation, and straining bonds.