How Do We Know That

Electron micrographs show us that mitochondria do contain many membranes.

Can you figure out what all this membrane surface must mean?

Membrane folds create more surface area for the attachment of the molecules used to generate energy. Think about the shirts folded in your dresser drawer. Could you fit the same number of shirts in the drawer if you wadded them up?

What's contained between the membranous plates?

Electron micrograph pictures show that surrounding the folds is a fuzzy background. How can we know what is there?

Mitochondria can be separated from cells by gently crushing the cells and then spinning the suspension in a test tube at high speed.
Because of their size and weight, mitochondria settle out in a definite layer.
"Pure" mitochondria can be obtained by using a pipette to suck out this layer.
Then, filtering out the membranes that make up the folds reveals that the rest of the material contains many chemicals, including DNA. This is called "maternal" DNA because it is inherited only from your mother. The purpose of this DNA is to direct the formation of new mitochondria when cells divide.

Mitochondria make a lot of energy, and the chemical reactions also make a by-product of oxygen free radicals. This is a highly reactive and toxic form of oxygen that can poison cells, which is especially serious for RNA and DNA. The DNA inside the mitochondria is an easy target, because it is already inside the mitochondria where the free radicals are being generated. Free radical poisoning is a special problem in nerve cells. Because neurons survive so long, the damaging effects in them can accumulate over time. This toxic effect may cause such brain diseases as Parkinson's Disease and Huntington's Disease. Prevention of free radical damage can perhaps be reduced by taking "anti-oxidant" vitamins, such as Vitamin C and Vitamin E.

A discovery made in the year 2000 revealed that certain proteins that are trapped inside these membranes can trigger cell death once they are untrapped. During certain stages of development and during aging, mitochondrial membranes break down to release these deadly poisons. This process is called "programmed cell death." Does this suggest that life span is dictated by genes from the mother? We are not sure because scientists have not looked into this!

How did we discover the functions of mitochondria?