Introducing Epigenetics: A Graphic Guide (Graphic Guides Book 0)

by Cath Ennis

Epigenetics is about how the genes* we inherit from our parents are controlled, and how they interact with our environment: how our genes make us, well, us.

Genes are made of deoxyribonucleic acid (DNA)*. DNA consists of long strings of four component molecules*, called bases*: A, C, G and T. The order, or sequence, of these bases along the string serves as our genetic code. Two long strings of DNA coil around each other to form the famous double helix structure.

A always connects to T, and C always connects to G.

The first step in translating the DNA’s coded instructions is called transcription*.

ribonucleic acid (RNA)*. RNA is similar to DNA, but its short, single strands are less stable and more mobile than the DNA’s long double helix.

DNA is too big to get through, so these RNA molecules act as coded messages from the genes to the rest of the cell.

Some of the RNAs that leave the nucleus are called messenger RNAs (mRNAs)*.

You don’t look exactly like your parents because their genetic material was shuffled before it was dealt to you; you don’t look exactly like your siblings because their shuffle was different. The exception, identical twins, come from a single fertilized zygote that splits in two.

Repetitive DNA is problematic. It can move to new locations; it can make the transcription and DNA replication machinery slip and stumble, causing mutations that contribute to cancer and other diseases.

This type of interaction allows for incredibly precise, tightly-regulated control over gene transcription. However, we’ve still barely scratched the surface of the complete histone code.

Breaking the attraction between the positively-charged histones and negatively-charged DNA requires a lot of energy.

Methylated ICRs are recognized and bound by a protein called ZFP57, which recruits partners that protect these regions from demethylation during the first epigenetic reset in early embryonic development.

When pregnant agouti mice eat methyl-rich supplements, such as folic acid,

The benefits of burning more calories, and of increased cardiovascular fitness and muscle strength, were relatively easy to explain – but why would exercise also reduce the risk of cancer, dementia and depression?

Exercise correlates with the silencing of genes that are involved in cell division and inflammation, which might help to explain the effects of exercise on cancer and other disease risks.

During the harsh winter of 1944–5, the Nazis blocked all food imports to the Netherlands, causing a devastating famine. It’s estimated that 20,000 people died of starvation before food supplies returned to normal with the liberation of the Netherlands in May 1945.

Epigenetic evolution therefore occurs in a way that’s fully consistent with the modern definition of Darwinism.

Mutations can be passed down from one or both parents, or can arise spontaneously in the egg, sperm or zygote. Familiar examples include sickle cell anaemia (caused by mutation of the haemoglobin protein that transports oxygen around the body) and cystic fibrosis (caused by mutation of a protein that pumps salt across cell membranes).

The disease is also immensely expensive, with over 100 billion US dollars spent globally each year on cancer drugs alone.

Cancer cells contain altered histone modification patterns,

Some cancer-initiating epigenetic changes are probably the result of random chance – drift (see here) – or an error during mitosis. Some environmental exposures can also initiate cancers via epigenetic changes. For example, DNA methylation patterns change after exposure to well-known cancer-causing agents such as tobacco smoke, and to new threats like Bisphenol A (BPA), a component of some plastics that has been found to leach out of drinking bottles and into the body.

human stem cells can be extracted from very early stage embryos, before they implant into the uterus. Surplus embryos from in vitro fertilization (IVF) procedures are typically used, with the parents’ consent.

In 2006, Japanese stem cell biologist Shinya Yamanaka (b. 1962) published a new method for creating stem cells directly from mature adult cells.

This means that we could use the patient’s own skin or blood cells to repair or replace their damaged tissues and organs,

The bases that make up RNA can also be modified. In fact, there are more than 100 types of RNA base modification.

A new DNA sequence editing technique called CRISPR can be adapted so that it edits epigenetic modifications instead of editing the DNA sequence directly. Part of a protein called Cas9 is used instead of a transcription factor’s DNA binding domain.

Epigenetic editing has only been demonstrated in cultured cells so far, and will have to undergo rigorous safety testing before it can be used in humans. If proven safe, this technology has the potential to treat cancer and other diseases

As technology improves, the amount of sequencing data generated is increasing exponentially

Individuals can also now undergo private DNA sequencing, to learn more about their health risks or ancestry.

Conrad Waddington first coined the word “epigenetics”.