Big things are always made of smaller parts. Think about an orange. From the outside, it just looks like an orange ball. When you cut it in half, though, you see that it is made out of many smaller and separate pieces. You can pull apart these slices and eat them one at a time. Look even closer and you will see that each slice is packed with even smaller beads. Each bead is filled with juice and this juice is what makes each slice taste sweet.
Just as the orange is made up of little beads of juice, all living things are made up of cells. Sometimes those cells work together to do one job, the way many beads of juice come together to make one slice of orange. Many smaller cells in your body join together to make parts like skin and bones. Then these large groups of cells work together to make one living thing. That's like the way all the slices of an orange come together to make one whole piece of fruit.
When you put it all together it tastes delicious.
Almost everything is made of smaller pieces. Not just the parts of our body, but the directions for how to make these parts too. People get these directions from their parents. They are called genes. Genes are the directions for our bodies that are found inside every one of our cells. These directions are not written in words like the ones you are reading right now, but just like the orange, they are made up of smaller parts.
These directions are found in every living thing. They tell the cell what kind of living thing to make, from a fruit fly to a monkey. They tell the cell exactly what that living thing will look like. The directions have information about size, eye color, hair color, even whether the living thing will have hair or feathers. They tell the cells what they need to do to keep the living thing alive. The directions for everything that happens inside a living cell is written in its DNA
Now hold on, how my genes are related to a human's?
DNA is like the alphabet that is used to write the directions inside cells. These directions are used to build every kind of living thing, from an ant to an elephant. The interesting thing about these directions is that they are written with just four letters. Think of how many ways you can group and arrange four letters. You could use the same four letters to spell "naps," "snap," or "pans." There are actually twenty-four different ways to arrange any four letters. Now imagine that you could use each letter as many times as you like. There is no end to the groupings you could make up. The order of the pieces of the DNA code in each living thing is called its sequence
. Each living thing has its very own sequence.
The letters of the code are arranged along two long ropes. Think of these ropes like the long sides of a ladder. The letters are arranged in pairs. These pairs form the rungs, or steps, of the ladder. DNA is in the shape of a twisted ladder.
You can get an idea of this by picturing a Slinky. Pull on each end to stretch it out. Now you can see how it is formed. You can see it is made of a wire that spins around and around, forming a coil. A spiral
is the name for something that curves and twists around in the shape of a circle over and over.
Remember that DNA is shaped like a ladder. It has two long sides. Each one of those long sides is in the shape of a spiral. Those two sides are joined together by pairs of "letters." DNA is shaped in a double helix. A double helix
is the name for two spirals that are connected to each other.
A double helix, the backbone of our genes.
Now you know that all living things have DNA inside them. You know that it is a set of plans written with only 4 letters. It tells the cells of a living thing what to do and how to work together. Thank goodness for DNA! Without it we would be nothing more than a lot of cells that do not know what to do!