When performing a song, knowing and reading musical notes is as important as doing it with the right rhythm. In the score, the musical notes are placed sequentially and different marks provide information on the register, speed or intensity with which they should be played.
The human genome functions in a manner similar to a partition, in that the DNA sequence contains the instructions for making proteins and other functional elements, and the epigenetic mechanisms regulate how and to what degree they are to be expressed.
Thus, if the genome comprises the complete DNA sequence, the epigenome designates the set of elements which regulate the expression of genes without altering the DNA sequence.
What is epigenetics for?
Essentially, all cells in the human body contain the same genetic material – or the same score, if we keep comparing genetics and music. However, not all of them express the same genes.
Each cell type, within each tissue, has a different genetic program, so only the genes they need are expressed. For example, in addition to the genes responsible for basic functions, neurons must express all the genes linked to the emission and reception of nerve signals. These genes, on the other hand, are not needed in other types of cells, such as the cells responsible for storing fat.
Plus, when cells express genes, they need to do so at the right time and in the right amount. How? ‘Or’ What? One of the methods by which they achieve this is through epigenetic mechanisms.
Epigenetic marks act as a memory for the cell and are reversible
One of the characteristics of the epigenome is that it is not static and can be modified. Throughout our life, the epigenome records the experiences of the cell, as well as the influence of the environment on them.
Therefore, the epigenome is different in different tissues and cell types in the body, it changes throughout life or during development and even in different health states.
What types of epigenetic mechanisms exist?
Here are the main epigenetic mechanisms. All of them are reversible, which means they can be changed.
DNA methylation is one of the most studied epigenetic mechanisms. It consists of adding a biochemical group called methyl to one of the units or nucleotides that make up DNA, cytosine.
Methyl groups located on DNA act as recognition signals for certain enzymes which affect gene expression. Methylation is generally associated with repression of gene expression.
Inside the cell nucleus, DNA does not appear isolated, but is organized with proteins and other molecules, forming chromatin. The basic unit of chromatin is the nucleosome, made up of DNA wrapped around eight units of histone proteins.
Histones can be biochemically modified in certain specific positions (reversible epigenetic modifications), which affects the degree of DNA compaction in the nucleosome and the accessibility of genes to all the enzymatic machinery responsible for gene expression.
The more compact the DNA is in a nucleosome, the less accessible the genes in that region are. On the contrary, if the DNA is less compacted, there is more space for proteins related to gene expression to bind to DNA.
Combinations of histone modifications define the state of chromatin and the activity of the DNA that makes it up. In addition, the location of nucleosomes also determines the accessibility of transcription factors to DNA.
Certain small RNA molecules can silence gene expression, bind to DNA, and interfere with transcription or the process in which information is transferred from DNA to RNA or binds to protein complexes. gene silencing.
The different epigenetic mechanisms interact with each other. For example, the cellular machinery responsible for nucleosome remodeling is influenced by DNA methylation and by changes in histones. Likewise, DNA methylation is a signal to recruit protein complexes that include histone-modifying proteins. When epigenetic mechanisms do not work properly, diseases can develop. One example is Rett syndrome, caused in most cases by mutations in the MECP2 gene which encodes a methylated DNA binding protein.
Epigenetics and environment
Epigenetics act as a bridge between genes and the environment. Certain environmental factors, such as the tab