you and your genome

That's right, you have a genome. And your genome is your friend. But what is a genome? And what is it doing for you?

Your genome is what makes you you. It is all the information required to build you... well, more accurately, it is all the information in your body that is required to build you (the external environment and your life experiences also play a very important part in designing you, but we will not be discussing that today). Essentially, your genome is your DNA (short for 'deoxyribonucleic acid' ...try saying that 3x fast!) and your DNA is your genetic blueprint. Lets start there.

DNA - it is in us all (in the form of 'chromosomes') and it is what makes each of us an individual. DNA is a very long string of letters, called nucleic acids. These letters spell words, that are called genes. Basically DNA is a more advanced binary code used by cells. There are four letters in the alphabet of DNA: adenine, cytosine, thymine and guanine (shortened to A, C, T and G). These letters are specific chemicals that are strung together billions of times to make a very long DNA molecule, which folds to form the classical 'double helix' structure that most of us have heard about. These four letters are used to spell all the genes in our body, and this string of DNA is what we call our 'genome'.

Essentially, our genome is a specific DNA molecule that is found in every single cell of our entire body, and that contains all the directions needed to build us. The specific genes that are on this string will make specific types of proteins, these specific proteins will make us a specific type of person. This phenomenon was discussed in the earlier post "Good Genes, what are they and how can I get some?" However our genome is a little more complicated than that. Although each cell contains the same DNA there are many levels of regulation occurring in our cells that control which genes are used and when these genes are used. This regulation is very important because how each cell uses the DNA will determine how that cell behaves.

Gene Regulation is very complex. It relies on specific
regions and chemical modifications that are on DNA
and that are used to tell a cell which genes to use. By
controlling the genes a cell uses we control how that
cell behaves, which is necessary in order to build the
different tissues that make up our body 

As I mentioned the same string of DNA is in every single cell of our body, but as we know the cells in our body are specialized for certain functions: we have skin cells, liver cells, blood cells brain cells, etc. So, how does the same script (DNA) direct so many different types of cells? Each cell type is specialized because of the genes it uses. A liver cell only uses liver genes, and only makes liver proteins. A brain cell only uses brain cell genes to make brain cell proteins. This is how a cell becomes specialized.

But how does a cell determine which genes to use?This is where gene regulation really comes into play. There are specific regions of DNA (called 'promoters' and 'repressors'), and specific chemical modifications (called 'epigenetic' changes) that are on DNA and that are used to tell each cell which genes to use, and which genes not to use. Some regions on DNA will 'turn off' specific genes, and some chemical modifications will 'turn on' other genes. It is the combination of 'on' and 'off' signals that determine the proteins a cell makes, and the way the cell behaves. This is how a liver cell 'turns off' the genes needed for a heart cell, which 'turns off' the genes needed for a skin cell, which itself 'turns on' the genes needed to build skin. Through these complex levels of gene regulation each cell 'terminally differentiates', a concept we learned about in the stem cells post. This is how a single string of DNA, our genome, directs all the cells in our body in order to make us a whole and complete individual.


A final interesting fact about genomes is that every organism has one. A bacteria, a fly, a mouse, a fish, a plant and an elephant all have a genome. And these genomes are all made up from the exact same four letters that make us up! What makes a mouse different from a fly is the set of genes that are encoded in their genome. Each animal and plant has a specific and unique set of letters in their string of DNA. In a fly's genome there will be genes to make wings and genes that allow it to lay eggs. In a mouse there will be genes that make fur and genes that build four legs. In a plant there will be genes to grow roots and genes to make seeds. If a scientist were to stumble upon a random string of DNA they would be able to determine the owner of that genome simply by looking at the genes encoded in it! This is how a criminal can be caught by leaving behind cells at the scene of a crime. DNA is that specific. It is amazing how every species on this planet are built using the same four letters! The diversity we see all around us is simply based on differences in how those four letters a strung together and used!

Related articles by Zemanta

• A Basic Introduction to Genetics and Genomes (ncbi.nlm.nih.gov)
• Cloning Extinct Species: How Close Are We? (singularityhub.com)
• Looking for the Purpose of Junk DNA (brighthub.com)
• Genome of ancient sponge reveals origins of first animals (sciencecentric.com)