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Epigenetics: The reason DNA isn’t solely responsible for who we are or what we look like

We are made of billions of cells, each genetically identical – they have exactly the same DNA. So why are some cells red blood cells, some skin cells and others brain cells? Surely they should be identical in every conceivable way? How can our red blood cells contain large amounts of iron whereas our skin cells contain large amounts of keratin, and have fundamental differences in their structures and purposes? This is where epigenetics comes in. Epigenetics, essentially, tells the DNA within our cells what to do. For example, whether or not to make iron or keratin. And this is why all the cells in our body work in exactly the right way.

Epigenetics controls our DNA in two ways:

1. Methylation

This is when a methyl group (CH3) attaches itself to our DNA, specifically the nitrogenous base cytosine which is usually attached to the base guanine, which is called a CpG motif. These CpG motifs are very frequent just above a specific DNA sequence called a promoter, which is where complexes bind to a specific gene and copy it into RNA. When this methylation occurs, the gene becomes “switched off” and no longer has an effect, as the specific protein that the gene would normally code for is not produced. For example, the gene for keratin is switched off in red blood cells. This occurs because when a CpG motif is methylated it binds to a protein called MECP2. This attracts other proteins which help switch off the gene and stops complexes binding to the promoter, stopping RNA production, in a process which can be near permanent.

2. Acetylation

DNA is coiled around spherical proteins called histones. These have an amino acid chain attached to them, like a tennis ball with a tail. An acetyl group binds to the amino acid lysine, resulting in DNA being coiled around the histone more or less tightly. If it’s coiled more tightly, its genes are expressed to a lesser extent. If it’s coiled more loosely, its genes are expressed to a greater extent. So, unlike the simple on-off switch of methylation, acetylation works more like a knob on a stereo, with expression occurring to certain degrees.

 

But here’s the worrying thing: these changes are a result of our external environment, so our lifestyle choices can affect our genetic expression. For example, if you live in a stressful environment for long periods of time, your body continuously produces large amounts of stress-related hormones. These can induce an epigenetic response meaning that, later in life, we become more anxious more easily. In fact, it’s even been claimed that this response has a link to post-traumatic stress disorder, the adverse effects of which are experienced by millions. Similarly, if we have a diet low in folic acids – some sources of which are leafy vegetables, peas, beans, sunflower seeds and liver – our methylation levels decrease and there is a clear link between this and the likelihood of developing cancer.

And what is perhaps significantly more worrying is that these epigenetic “marks” can be passed down from generation to generation (trans-generational inheritance). So, our choices affect the health of our children and grandchildren, since every action we make now has a consequence for them. This is already scary enough in such a perfectionist society, as this means we could create a generation disadvantaged in so many ways (obesity and diabetes, post-traumatic stress disorder, susceptibility to cancer; the list goes on). Furthermore, our unhealthy lifestyles aren’t just putting pressure on our health services currently, but also over, potentially, the next 200 years.

But what are we meant to do about it? We must take more interest in funding epigenetic research in order to discover other factors that could influence childhood health. After this, we must make changes to our lifestyles to reduce our exposure to these factors. If our government is not aware of the severity of such a phenomenon and we are not aware of its effects, our health services will be unable to cope with the drastic increase in hospital admissions due to epigenetic problems.

But, in the meantime, we must watch our diet and lifestyle, since if we are optimistic, epigenetics could be more of a gift than a curse. It could help us improve our lives simply through a healthier way of life. What is more, people are already realising this, like scientists from the University of Alabama, Birmingham (UAB), who have shown that vegetables such as broccoli and cabbage contain compounds that could help to reverse or prevent cancers and other ageing-related diseases as part of the “epigenetics diet”. Our mums are always right in the end!

Epigenetics is defined as the study of changes in organisms caused by modification of gene expression rather than alteration of the genetic code itself. So, our experiences effectively determine how our DNA affects us without changing our DNA itself. It turns out we really are what we eat after all!