The human body is made up of millions of CELLS. Each cell does a specific job in the body, for instance a red blood cell carries oxygen around to places that need it, and a nerve cell carries signals to and from the brain.
Every cell is like a bag of chemicals. The bag is called a CELL MEMBRANE. It does an obvious job of stopping the inside of the cell from leaking out and unwanted things from getting in. The CELL NUCLEUS is the information store of the cell. A very special chemical called DNA is kept in the nucleus. The DNA is a chemical blueprint that tells the cell what other chemicals to make, and so what job the cell will do in the body.
Inside the cell are thousands of little structures called MITOCHONDRIA (pronounced MITE-OH-KON-DREE-AH)
The mitochondria are the powerhouses of the cell. The chemical reactions that
release energy from food go on inside them.
When we are only talking about one, we call it a MITOCHONDRION.
A Mitochondrion is like a tiny cell itself. It has an OUTER MEMBRANE that keeps the mitochondrion in a tiny sausage shape. Inside this shape, there is another membrane, called the INNER MEMBRANE.
The Inner Membrane of a mitochondrion is not just a bag like a sausage skin. Embedded in the membrane are the chamicals that turn food into energy. These chemicals work by pumping Hydrogen ions across the membrane, to build up a 'gradient'. When the Hydrogen ions flow back the other way, the energy is used to
make a chemical called ATP. This ATP chemical is the fuel of the body. It is passed around the cell to where it is needed. When the cell needs to do work, it splits some ATP to form ADP and energy.
The Inner Membrane is folded so that more membrane can be packed inside the mitochondrion. This gives more space to put these chemicals that rurn food into energy and so allows the mitochondrion to provide more energy to the cell.
There are several genetic defects which can cause LHON. They all change the structure of these chemicals embedded in the mitochondrial membrane. Changing the structure
of the chemical makes it less good at its job, so the body gets less energy.
Studies have shown that some people with LHON have mitochondria which work 70% less effectively than they should.
There is also a study which shows a drop in the glucose metabolism
of the brain in affected people as comapred to unaffected family members.
It is this lack of energy that causes the problem. Just like a car running out of fuel, the cell can't function properly and stops working.
These chemicals inside the mitochondrion are not part of the blueprint held in the cell nucleus. Each mitochondrion has its own DNA inside, which is the blueprint for the chemicals inside the mitochondrion. The genetic defects which cause LHON are in the DNA held inside the mitochondria.
The DNA inside the nucleus comes from two places. Half is from the person's mother and half is from the person's father. However, ALL of a person's mitochondria come from the mother. This is why only the mother can pass on mitochondrial DNA, and so only the mother can pass on LHON.
