We hear about them all the time – this gene causes a disease, or that gene is important for normal heart function. Most people could tell you that your genes are made of something called DNA, that you inherit them from your parents and pass them on to your children, and that they determine much of who you are and what you look like. But how do we get from genes to an entire organism, and what control do we have over our genes?
To answer these questions, we need a basic understanding of what is known as the “central dogma” of biology, which describes the one way flow of genetic information. While the reality is more complex than this, the flow can be simplified as such:
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DNA (genes) – a permanent store of genetic information
RNA (messenger) – short, temporary copies of a single gene transcribed from DNA
Protein – functional molecules that are built by translating genetic information from RNA
Each of the three stages is chemically different, but they all share two critical properties.
- They are made up of repeating units that are bound together like links in a chain. In the case of DNA and RNA, each link in the chain can be one of four different bases; in the case of proteins, links can be any of 20 different amino acids.
- The sequences of these different links are critical. The base sequence of DNA determines the base sequence of RNA, which in turn determines the amino acid sequence of proteins; the amino acid sequence of a proteins determines that protein’s shape and function.
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We can think of these different links in DNA or protein as like letters in an alphabet. The English alphabet has 26 letters, and taken alone, each of them is quite meaningless. However, we can put them together one after another in many different sequences to form meaningful words, sentences and entire novels with almost limitless possibilities. In the same way, proteins, built from just 20 different amino acids, perform the vast majority of all functions in any organism, whether it be breaking down sugars and fats into energy, moving our muscles, sensing the world around us, or providing structure to cells and tissues.
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The genes we are born with are, for the most part, the genes that we die with. Their sequences are rarely changed, and in that regard, our genes cannot be controlled. What can be changed, however, are the processes that come afterwards. Our behaviour (such as diet and exercise) and our environment can turn transcription and translation on or off, or make small modifications to proteins in order to turn their function on or off.
Nathan Scrimgeour, senior engineer at CERG