How cell membranes shape our life
Posted by Åse Dragland
Life requires two things: a membrane that can distinguish between nothing and something, and that this “something” must be an organism that is capable of reproducing.
Some time ago, American scientists created a protein that behaves just like primitive enzymes did when life evolved on Earth. This chunk of protein consisted of two chains, each of which contained 31 amino acids. The scientists also managed to produce membranes shaped like part of the bacterium.
The question is whether life could have emerged in this way; that genetic material was accidently captured inside a membranous envelope, and that this was what led to further evolution.
The basis of all life
One thing that is certain is that super-thin membranes – which may be only a a few nanometres (millionths of a millimetre) thick – are to be found everywhere within us and around us, acting as a sort of wall that allows certain types of molecule to pass through it, while keeping others out. And they are more important and powerful than most of us realise.
The best-known is the eardrum, a thin membrane that protects the inner ear and is also set in motion by sound-induced vibrations, converting sound-waves into minute movements of the bones of the inner ear; movements that we perceive as sound.
Organic membranes are also essential in the world of plants. Photosynthesis, the process whereby plants use light from the Sun to convert CO2 into organic compounds such as sugars, and oxygen, is one of the most important natural processes on Earth.
This is a sophisticated system with a highly regulated shuttle traffic of ions and molecules that passes through several membranes. It has been said that all higher life-forms would actually die out within 25 years if this process ceased to take place!”
Do cell membranes shape our lives?
In our own bodies, membranes surround every single cell. These membranes are so fine that they were not discovered and confirmed until modern electron microscopy arrived in the late 1950s. For this reason, it is only recently that scientists have discovered the roles played by membranes in our bodies.
Not only do membranes separate the interior of the cell from the external environment, but something in the membrane itself makes important, and correct, decisions about which substances can pass into and out of the cell. The membrane simply treats different molecules in different ways: toxic or unnecessary substances are not permitted to enter.
Cell biologist Bruce Lipton, who has taught in the schools of medicine at both the University of Wisconsin and Stanford University, has dedicated all of his career in research to cell membranes.
He claims, controversially enough, that membranes, rather than genes, are what shape our lives. It is in the membrane that the active intelligence of the cell is to be found. The membrane receives signals from the cell’s environment, depending on which molecules attach themselves to the membrane wall; it interprets the signals and tells the cell what to do; and these signals we largely create ourselves through stress, nutrition and feelings, claims Lipton.
Membranes created by man
We ourselves have learned to simulate the fantastic membranes of the plant and animal world for our own purposes.
Inorganic membranes lie under the tiles on our bathroom floor, filter out bacteria from our drinking water and are found in industrial fuel cells. Membranes are used in structures that need to withstand water pressure. They are used in gardens, under roads and in all sorts of ponds and reservoirs.
Energy and climate
SINTEF scientist Rune Bredesen and Thorleif Holt have been working on membranes for several years. One of them does research on the use of membranes to improve the efficiency of CO2 scrubbing, the other on membranes as the basis of saline electricity generation.
The world’s first prototype saline power plant was built at Hurum outside Oslo last year. It mixes freshwater and seawater through membranes, and is able to extract energy via osmosis. All over Europe and in the USA, teams of scientists are using membranes in saline power plants. One of SINTEF’s tasks is to help develop the optimal membrane for the Hurum plant. Thorleif Holt and his colleagues have tested hundreds of candidates, but have not reached their goal yet.
What role does the membrane play in a saline power plant?
“It operates according to the same principle as in an animal cell; certain substances are allowed to pass through it, others are not. Freshwater and saltwater are put into the same tank, separated only by a membrane. It is in the nature of the freshwater to force its way through the membrane to dilute the saltwater, which increases the pressure in the saltwater’s section of the tank. The freshwater passes through the membrane, but the saltwater cannot.”
Holt and his colleagues have concentrated for the most part on sheet membranes. But the layers need to be made thinner and more porous, and it is important that the water is able to penetrate them. At the same time, they need to be strong.
Membranes for a cleaner world
Meanwhile, Rune Bredesen and his team of scientists are working on materials designed to capture CO2. In a field that is currently regarded as one of the most important topics in applied science, membranes are an essential part of the picture.
The world is short of energy, and one method of generating electricity is by burning natural gas. The problem is that when natural gas is burned, the carbon in the gas reacts with oxygen in the air to produce CO2, which should not be emitted to the atmosphere.
The current debate regarding natural gas power stations centres on how we can lower the cost of carbon capture sufficiently to make it worthwhile to use this as a technique. Both Bredesen and his colleagues at the University of Oslo and NTNU are trying to find the cheapest and best way to do this. This means that the gas-scrubbing process must not use too much energy.
“There are many ways of scrubbing gases,” says Bredesen. We are putting a lot of effort into removing CO2 before the gas is burnt in the power station; this is known as “pre-combustion technology”. Natural gas or coal is converted to hydrogen and CO2. We then use membranes to separate the two gases. When we have separated out the combustible hydrogen, we are left with CO2 that is easier to deal with, and can be stored. We use the hydrogen as fuel for electricity generation.”
The hydrogen membrane from SINTEF appeared to offer the cheapest and most efficient CO2 capture in an EU carbon capture project, in which 24 partners participated and four different technologies were evaluated and compared in terms of cost and efficiency.
Now the scientists are about to scale up the technology involved, since a gas-fuelled power station will need several thousand square metres of membranes.
Can bio-membranes combat global warming?
But can humanity actually control the cycle and conditions under which life exists?
Yes, believes Norwegian company Albedo Technology International, which claims that its special reflector membrane could help to control the temperature of the Earth’s surface.
Between 2007 and 2009, the company carried out a series of tests in the Sahara desert, where it sprayed its product on the ground in order to create a reflective film, which lowered the surface temperature by 45 degrees Celsius. On a one million square metre test field in Morocco, the company tested several versions of its product, and climate scientists at Norway’s Cicero climate research centre confirm that the biomembrane has great potential if it can be made to stay in place on large areas for long periods of time.
The company is now about to start a parallel research project in the Arizona desert in the USA, that will document what sort of changes take place when large amounts of energy are reflected back into space from the Earth’s surface.
It remains to see whether the bio-membrane will come true. In any case, we may ask whether the “original” biological membranes, in the course of their faithful everyday efforts to keep our bodies and life in Earth in general, going, are still the most advanced systems available.
Illustration: The eardrum lies in the auditory canal. The membrane system deflects tiny hairs in the cells of the cochlea in the inner ear, which are what enable us to hear sounds. Credit: Line Halsnes
Åse Dragland is the editor of GEMINI magazine, and has been a science journalist for 20 years. She was educated at the University in Tromsø and Trondheim, where she studied Nordic literature, pedagocics and social science.