The importance of oxygen - The chemistry of almost everything (14/31)

Uploaded by OUlearn on 03.09.2009

I think it's very important to understand what it is that causes death.
Because we begin to recognise, as we understand these processes,
that what they are, are perfectly natural,
biological and chemical responses to our surroundings.
What happens in a heart attack is that the heart stops pumping.
Either it stops completely, which is called cardiac arrest,
or it starts a very complicated rhythm that is ineffective in pumping blood out.
So, really, in a heart attack,
what we have is the ultimate deprivation of the cells of their oxygen.
And the cells die and, most particularly, the brain cells die,
because the pump is no longer effectively driving the blood to them.
It's useful stuff, this oxygen.
But two thousand million years ago when it was all starting to happen,
terrestrially speaking,
I mean, neither of us would have stood a chance.
You see, there was no oxygen in the atmosphere then,
just nasty gases like methane and ammonia.
And it wasn't until the first plant life showed up
and started to photosynthesise, that the oxygen began to appear.
It was perhaps the worst case of air pollution ever recorded on this planet.
Because the organisms living at the time were anaerobes,
they thrived in a reducing environment, and then, all of a sudden,
you're presenting them with an oxidising environment.
And they didn't like it. Present-day anaerobes are killed by oxygen.
So, presumably, those anaerobes didn't like it, either,
and they either had to retreat to environments
that the oxygen didn't penetrate,
or dispose of the oxygen in some way,
or they could maybe evolve to use the oxygen,
but they also had to also had to evolve protective mechanisms,
what we call anti-oxidant defences.
Some organisms evolved surface enzymes that just used oxygen
and reduced it to things like water or hydrogen peroxide,
so it didn't get into the cell.
But the big advantage was really the evolution of aerobic respiration,
which, firstly, helped to use up oxygen,
but also enabled organisms to, very efficiently, produce energy.
Aerobic respration is about 14, 15 times more efficient
than anaerobic respiration.
If oxygen is now the very basis of life, it's still something of a double-edged sword.
Babies born prematurely pose a special dilemma for doctors and nurses.
Because their lungs and respiratory systems are underdeveloped,
they need to be given higher doses of oxygen
to sustain their fragile grasp on life.
Obviously, we all need oxygen to survive but, in fact, oxygen is toxic.
And oxygen is toxic not because of its own reactivity, which is rather feeble,
but because it's capable
of being involved in a variety of reactions in the body,
some of which occur normally,
which can lead then to toxic species, as we call them.
And these species are free radicals.
Over the last 20 years there have been tremendous advances made
in the ability to keep premature babies alive.
So much so that many babies that are born around 22, 23 week gestation now,
are surviving.
The problem we have is that we have to give these children
an awful lot of oxygen.
And we know that oxygen in high quantities
will lead to increased radical production.
The body is made up of tissues and cells,
and they're all made up of molecules.
And within those molecules are electrons.
And the important thing is that electrons like to be paired.
They go around in pairs, and that's their stable configuration.
A free radical is a molecule with an unpaired electron, so, clearly,
its task in life will be to find another electron to pair with to make it stable.
So, it will attack whatever's around,
pull another electron from there to pair its own electron.
But, in so doing, will leave behind an unpaired electron.
So, this will initiate a cascade of reactions
where electrons are being passed from one to the other,
and in the process can cause damage to the cells of the body.
One of the things which free radicals do,
is it actually prevents those normal processes
of protein synthesis and DNA synthesis. So, the tissues don’t grow normally.
A further complication is that babies born prematurely
haven't had the time to develop their anti-oxidant defences.
The way the body naturally copes with the toxic effects of oxygen.
The body is brilliant designed. It's constantly being attacked,
not only by free radicals, but by all sorts of poisons that we eat in our food,
in all sorts of poisons that we breathe in the air.
So, the body has to survive by developing a whole series of
defence mechanisms against natural hazards.
Perhaps the most beautiful one of these
is the one that really deals with these toxic by-products of oxygen.
This is called the anti-oxidant defence system of the body.
It comprises things like Vitamin E, Vitamin C,
and a series of enzymes and proteins
which are strategically located in different parts of the cell,
so that they can neutralise radicals as and when they're produced.