2. DNA, Genes & Chromosomes

What you need to know...
  • What are DNA, genes and chromosomes?
  • What do genes code for?
  • Why are we unique?
  • How do we inherit characterisitics from our parents?

DNA, Chromosomes and Genes.

You may remember from S1 that the nucleus controls the activities of the cell. This is because the nucleus contains a very special molecule which provides the instructions for a living thing. This molecule is DNA.

DNA is a very long molecule because, as you can imagine, there are many, many instructions needed to make a living thing. To get all of these instructions to fit into a tiny cell the DNA is wound up very carefully into structures called chromosomes.
Chromosomes from Wikimedia Commons
DNA provides the code for proteins

Now let us take a closer look at a simplified model of DNA:

This shows us that DNA is made up of four different chemicals. These chemicals can be represented by the letters: A, T, C and G.

We can read the message by reading one side of the molecule from top to bottom. In class you will get the opportunity to decode some DNA messages!

If we decode the message in real life what we get are actually instructions to make lots of different proteins. These proteins will work together to make a living thing! Some of these proteins will be messenger molecules called hormones, some will form the structure of our tissues, some will help chemical reactions take place.
So remember:
  • The long molecule which contains the genetic blueprint for life is DNA.
  • Found on chromosomes, a bit of DNA which codes for a protein is called a gene.
  • DNA is organised into rod like structures which are called chromosomes.

Why are we unique?

We are all unique because our DNA is unique. Our genetic code is 3 billion letters long and these can code for many different characteristics. Different combinations of charactersistcs make us all different. Only identical twins have identical DNA. The uniqueness of our DNA is useful to forensic scientists who can identify people from the smallest sample of DNA.
Where do we get our genes?
We inherit our DNA and our genes from our parents. Half our DNA come from our mother, half our DNA from our father. If we know what versions of genes two parents have we can predict the chance that children will inherit certain characteristics. This is useful where parents know that they may be a carrier for a genetic condition.