Think of your classroom.  There are desks, chairs, people, paper, pencils, and the list goes on and on.  Each of these is a different part of the classroom.  Each adds something that's needed by the teacher and students.  Chairs are for people to sit in, desks give people a place to set their things, paper can be written on, and pencils are what people use to write.  Everything has a different job, and all the pieces come together to make one classroom.

Hey, where did everybody go?

Ildar Sagdejev (Specious), CC BY-SA 3.0 , via Wikimedia Commons

Your body is just like that.  You are made up of many very small parts called cells.  They do not all look the same, and many of them have different jobs in your body.  The cells in your heart and the cells on the skin of your big toe look a lot different, and they also do very different things.  Your cells all work together to keep you going.


All living things are made up of cells.  These cells do not just sit there and take up space, though.  They are always changing.  You may have seen this when a tree leaf changes color in the fall.  The leaves stop making energy for the tree and shut down for the winter.  As the days get shorter in the fall, chemicals act together in the cells of the leaf telling them to stop making food, and the leaf will never be green again.  Any time chemicals come together and cause a change, it's called a chemical reaction.


Sometimes changes happen when new things are made.  If you put a fruity powder, like Kool-Aid, into water and mix them together, your get a fruit drink!  You took two different things and mixed them together to make something new.  If you mix eggs, flour, and sugar into a bowl and bake them, you make a cake!  Plants make their own food too, but they do it inside their cells with sunlight, water, and air.  When a change leads to something new, it's called synthesis.


Change can also happen when things come apart.  That's what happens when the green disappears from leaves in the fall.  When you eat food your body breaks the food into very, very small pieces that it can reuse.  New things can be made when chemicals come together or break apart.  In either case, a change happens.


These changes can be fast or slow, but living things need changes to happen as fast as possible.  They need to get on with the business of living.  To help these changes happen faster and easier there are special chemicals inside the cells.  They get changes going with a bang.


Say that you are sleeping one morning.  Your dad calls you to get up.  You will get up on your own, sooner or later, but then your little sister comes into your room.  She leans over you and shouts "GET UP!"  You will be out of bed fast, chasing her away.  If this change were going on inside your body, your sister would be the chemical that got things going.  An enzyme is a chemical that speeds up how fast things happen in your cells.


Each enzyme has only one job inside a cell, so there are many, many different kinds of enzymes.  They are all made up of a certain kind of stuff called protein, but it must be arranged just right.  It's a lot like words.  Words are made up of letters, and the letters must be in the right order or you cannot read the words.  Enzymes are made of lots of protein, but they must be in a certain order or they cannot do their jobs inside the cell.  Proteins are very important chemicals that make up your enzymes and many other parts of your cells.


Enzymes are like keys sitting in your pocket, waiting for you to need them.  In your body they float around inside cells, waiting for the right thing to fit into, or the right things that fit onto it.  When the right chemicals are there, the enzyme grabs them and makes a change.  This gets changes going faster than normal.  After it does what it's supposed to do, the enzyme waits around in the cell until the right chemicals are there again.

Enzymes - the body's key to chemical reaction.

MediaPhoto.Org, CC BY 3.0 , via Wikimedia Commons

These changes happen all the time inside you and other living things.  You do not even notice most of them.  Try this: put a piece of bread in your mouth and hold it there for 30 seconds.  What happens?  It will start to taste sweet.  Enzymes in your spit are already starting to break down parts of the bread.  It's being broken down into sugar.


Breaking down food is one of the enzymes' most important jobs.  This job is so important that they start to work in your mouth, even before you start to chew!  If enzymes weren't there to break down food in your mouth, it would take weeks, instead of hours, to digest your food.


Sometimes people are missing enzymes.  For example, some people feel really sick if they eat something made with milk, like cheese or ice cream.  They might get cramps, gas, or have to go to the bathroom a lot.  These people are "lactose intolerant."

I can't eat anything down this aisle.

This happens because they are missing the enzyme they need to digest the sugar in milk.  No other enzyme can take its place.  People with this trouble can eat dairy foods, but they must take a small pill first.  Otherwise, they will suffer.  See how important just one little enzyme is?  All this time they have been at work in your body, and you had no idea they were there!