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?