字幕表 動画を再生する 英語字幕をプリント What is a protein? We often think about protein as a nutritional requirement. You eat meat because it has a lot of protein. But proteins are far more than just food. Proteins are made of a string of smaller building blocks called amino acids. Amino acids are kind of like Legos that can be used to build proteins with different structures. When we eat our food, we break down the proteins that we ate into amino acids and then we stick them back together again to make lots of different types of proteins to do jobs in the cell. Here are some things that proteins can do: detect light, form hair, and fight disease. Let's look more closely at three examples. One: proteins move you. The reason that meat has a lot of protein is that meat is muscle. Muscle has to contract to move our body, so it's full of a type of protein that moves stuff around. Let's see how that works: here are some proteins in the muscle fiber. This protein, called myosin, can change its shape. When it changes shape, it moves these fibers relative to one another. Millions of these tiny movements cause the whole muscle to contract. Two: proteins can kill you. Botox is a protein that cuts up molecules in nerve cells that control your muscles. This means that Botox makes your muscles relax. This can be handy to reduce wrinkles for Hollywood actors, but it's not so great with the muscles controlling your lungs stop working after you eat food contaminated with botulism. Three: proteins speed things up. Enzymes are proteins that make reactions go more quickly. For example, the enzyme amylase helps break down starch into sugar. You have amylase in your saliva. Try chewing a piece of bread for a really long time. Keep chewing! What do you notice?