Epigenetics an Overview

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DNA is made up of four chemical bases, the sequence of these bases determine the information that will be copied for protein manufacture. A change in this sequence is referred to as a genetic mutation.
For example CATCATCATCAT a change in sequence would be CATCCTCATCAT. Genetic mutations can vary between the replacement or deletion, of a single DNA base to a large segment of a chromosome, they alter the type or amount of proteins manufactured and can be caused by environmental toxins, smoking or sun exposure etc. Only a small percentage of mutations cause genetic disorders and often gene mutations are repaired by the cells repair
mechanism.
Epigenetics refer to all heritable changes in the way a gene is expressed, other than modifications to the DNA sequence itself and is necessary to allow our cells to specialize. A good example of epigenetics in action is a developing baby. All the cells in our body have exactly the same DNA, however as the embryo grows it switches genes in different cells on or
off. Only a small percentage of genes are switched on in each cell. For example, all the genes for making eye cells, have been switched on in eye cells, ensuring the development of an eye, however all the other genes for kidneys and other organs etc. will be switched off in the eye cells. The eye cells and kidney (or other cells) are therefore genetically the same, but epigenetically different.
This process is what drives development, beginning with a single cell that continues to divide and multiply, activating and silencing genes to form many different cells, like neurons, muscles and blood vessels until your baby is ready to be born. Epigenetics is responsible for the many differences in human appearance, health, growth, etc. even different levels of thinking. Our bodies continues to divide cells throughout our lives and as we age, our cells have to continue to repair the accumulating damage to our DNA caused by sun, environment or smoking. When this damage is not repaired properly cancer and other problems can occur, more and more serious illnesses continue to be linked to epigenetics, the process gone wrong.
An Epigenetic mutation would therefore mean the sequence of DNA bases are still the same, but a gene have been switched on that is supposed to be off, or off instead of on. For example when a tumor suppressor gene is switched off instead of on, it can cause cancer to spread unchecked. Our cells also have a self destruct mechanism, when normal cells are damaged they go through a process of apoptosis (cell death), this is a protective mechanism that prevents them from multiplying into more damaged cells. Researchers found this mechanism altered in some cancer cells, explaining why chemo therapy can kill normal cells but some cancer cells continue to survive.
Epigenetic mutations occur much more easily than genetic mutations because epigenetic factors that influence gene expression are much more sensitive to diet and environmental influences.
Epigenetic factors that can influence gene expression include:
1. DNA Methylation
2. Chromatin Structure
3. Small RNA’s

1. DNA Methylation
A process where a methyl group (small chemical residue) is added to strategic bases on the DNA. The methyl group stops the transcription machinery from docking and thereby switches the gene off. A gene that is switched off cannot manufacture proteins, the building blocks of life.
Even though DNA Methylation paterns can be passed on from cell to cell, they are not permanent. Changes in DNA Methylation can occur throughout our lives, some of which are thought to be due to an individuals’ environment and diet. Methylation also plays an important role in regulating gene activity involved in memory formation. In a study on rats given drugs that inhibit methylation, researchers found that the level of methylation directly controlled the activity of genes known to either suppress or promote memory formation.
Dr. Ryszard Maleszka completed some very interesting research on bees. Dr. Maleszka says Royal jelly seems to chemically modify a bee’s genome by a process called DNA methylation and disrupts the expression of genes that turn young bees into workers.
When the gene that controls DNA methylation was silenced without recourse to royal jelly they discovered that the larvae began to develop as queens with the associated fertility rather than as infertile workers. Royal jelly is a food substance secreted by adult bees that is fed in some measure to all young bees.
DNA Methylation also plays an important role in the regulation of Chromatin Structure.
2. Chromatin Structure - how DNA is packed.
Approximately 2 meters of DNA, is packed with a protein structure into the nucleus of a human cell, of only a few micrometers. This means that some of the genetic information needs to be very tightly packaged. Like a very long string of beads (DNA the string) this structure can be folded to form different shapes, the winding and twisting hides the DNA sequence from the transcription enzymes that reads the genetic information and in doing so, these genes are silenced or effectively turned off.
According to Professor Rob Marthienssen Ph.D, about a tenth of our DNA stands aloof, spending it’s time in tightly packed clumps called heterochromatin, and unwinding only to replicate when a cell divides. The same sequence of nucleotides in two people can produce different patterns of gene expression if the way the DNA is clumped happens to
be different.
The DNA can also be packed together differently into chromatin, resulting in chromatin with different structures. The consequential structure of the chromatin also influences how genes behave.
The chromatin structure can be influenced by temperature, the developmental stage of
the organism and small RNA’s.
3. Small RNA’s
DNA makes RNA, and this RNA is primarily involved in making protein, the building blocks of our bodies.
Small RNA’s however do not make protein , they are involved in many different functions.
Small RNA’s are also involved in;
· Chromatin structure,
· Blocking the ability of other RNA to make protein thereby switching off or silencing genes.
· Directing DNA Methylation
· Directing different developmental stages
· Providing virus protection
Small RNA’s offer the biggest window of opportunity in genetic medicine and is the fastest growing area of research today. Expect small RNA’s to be the source of many discoveries in the future.
To view a fantastic, easy to understand metaphorical explanation on how Small RNA’s
protect our bodies from viruses, go to http://www.pbs.org/wgbh/nova/sciencenow/3210/02.html and click on RNAi explained.
References;
Backgrounder: Epigenetics and Imprinted Genes,

http://www.hopkinsmedicine.org/press/2002/november/epigenetics.htm

Epigenetics?, http://www.epigenome-noe.net/aboutus/epigenetics.php
Weinhold, B., Epigenetics: The Science of Change,

http://www.ehponline.org/members/2006/114-3/focus.html

Epigenetics, General Information, Inheritance

Born Smart » Epigenetics Overview

Epigenetics an Overview