What are we made out of?

Protein, Genetic code, DNA, Gene…

A human being is made out of 100’000 billion cells… Each one has a nucleus, in which there are 23 pairs of chromosomes; one of the chromosomes comes from our mother, and the other from our father. A chromosome is made out of a long twisted thread of DNA (the double helix). DNA is a succession of 4 different nucleotides, known as A, T, G and C. There are 3 billion nucleotides spread over 23 chromosomes! This is what is called our genome, i.e. our biological identity and the genetic heritage we pass onto our children.

Much like a recipe book, each chromosome contains a certain number of recipes, known as ‘genes’. Over 20’000 genes are recipes for proteins. When a cell needs proteins, appropriate genes are ‘copied’, and the copies (called messenger RNAs) are transferred to the ribosomes, where the proteins are made. It is thanks to our proteins that we are able to breathe, to walk and to sense things. Without proteins, there is no life.

The cell

The building block of all living beings

The human genome

= 23 pairs of chromosomes

A chromosome

= very long twisted threads of DNA


= a succession of nucleotides: A, C, G et T. A always binds T, C always binds G

A gene

= portion of DNA that contains one recipe to make one protein, for example

Messenger RNA

= copy of the recipe which is transferred to the ribosome

A ribosome

= a protein factory. The ribosome reads the information held in the messenger RNA and translates it into a protein, using the genetic code

A protein

= a succession of amino acids. Proteins have a lots of different shapes, and lots of different functions