Introduction to epigenetics

Published on February 27, 2020   26 min

A selection of talks on Cell Biology

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I'm Dr. Suzanne Ruddy from University College London, and I'm going to discuss epigenetics at an introductory level in this lecture.
What exactly is epigenetics? The word stems from the Greek epi, which means upon, close, or above. An epigenetics really relates to chemical additions to the bases in the DNA sequence. So it's a form of inheritance, but not as we've known it before. The bases themselves are not removed or changed with a different base, but they are changed by the addition of little chemical groups. You can think of it like accents in a language, where the accent changes the way the word is spoken and may also change its meaning. In a similar way, these chemical additions to the DNA can alter the expression pattern of the DNA itself. So epigenetics refers to inherited phenotypic changes that are caused by chromatin changes rather than actual changes of the bases present in the DNA themselves.
There are three mechanisms involved, and I'll discuss each of these in turn. The first mechanism to be discovered was DNA methylation, shown here. The second has been that of histone modifications, that I will discuss in the middle part of the lecture, and towards the end of the lecture, we will talk about non-coding RNA. What I will discuss is long non-coding RNA and how it interacts in an epigenetic way.
Let's start with DNA methylation. This is commonly found in many eukaryotes, including animals, plants, fungi, and bacteria. What it means is that methyl groups, CH3, are added to the cytosine that's present in the DNA. You can see that on the left, an unmethylated cytosine, and on the right, a methylated cytosine, where the CH3 group has been added on at the five-carbon position. This is shown in a sequence on the right-hand side of the slide, where the cytosine is followed by a guanine with a phosphate group in between to indicate that it is on the same strand. So in the sequence of DNA shown below, the red CGs in the five prime to three prime direction, the cytosine of that pairing would be a potential candidate for DNA methylation.