Podcast transcript

Podcast transcript

The water molecule

 Professor Nick Hoogenraad

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Liam Lenten

Hello. I'm Liam Lenten, a senior lecturer in Sports Economics at La Trobe University and you’re listening to a La Trobe University podcast.

Matt Smith

All right. That’s better. Hello everyone. Welcome to the La Trobe University podcast. I'm your host, Matt Smith, and this is Act 3 of Water and my guest today is Nick Hoogenraad.

Nick Hoogenraad

My name’s Nick Hoogenraad and I'm Professor of Biochemistry and the Head of School of Molecular Sciences and I'm Director of the new La Trobe Institute for Molecular Science.

Matt Smith

Now so far in our little series of water, we’ve learnt about the philosophy of water use and what we think about when we use water, and we’ve also looked at the legal side of water. So I thought I'd get Nick in to tell us about water itself, the very basic structure of it, the molecules of it, when you really get down to it, what is water made of?

Nick Hoogenraad

There are two hallmarks if you like, signatures, about life. One is water and the other one’s the carbon atom. And it’s interesting that, and perhaps not surprising, that when they launch deep sea probes, and I think one’s been going for many years now into deep space and still signalling, they put, besides the obvious, a drawing of a naked human, a man and a woman. They also put two other significant things inscribed on the outside of the space crafts and one is the structure of water, H2O, hydrogen connected with a single oxygen atom, and the other one is the carbon atom, because the carbon atom is the basis of life and water is not possible without life. So there’s something very special about water and we should go into that.

Matt Smith

So, we’ll start out with the basic structure then. The water molecule, how is that built?

Nick Hoogenraad

The water molecule is based on an atom of oxygen and the oxygen atom shares an electron in its outer shell with a hydrogen atom, which has two sides – it has the hydrogen atom and so we call these bonds covelant bonds – they’re strong. You can’t break them without extraordinary effort. The bonds are actually formed by the sharing of an electron, one from carbon with one that’s missing from oxygen, so it plugs into that gap on both sides but the sharing is not even. The nucleus of the oxygen atom is so much larger than carbon that it tends to pull on these electrons more strongly, and so if you put in your mind, picture the sharing of these electrons, they’re not exactly equi-distant from the hydrogen atom and the oxygen atom. So they’re closer to the oxygen atom, and because electrons are negatively charged, this means that oxygen carries a small negative charge on it. On the other hand, because everything needs to balance in life, the hydrogen has a slight positive charge on it, which means that water is actually what we call a polar molecule – it has small charges on it.

Matt Smith

That’s how it’s structured together. So how does that water molecule bind together with other water molecules to create water?

Nick Hoogenraad

So as a result of that, because you’ve got these little charges, one water molecule becomes glued if you like to another molecule, positive to negative. The hydrogen has a positive charge and the oxygen a negative charge, so you might be able to picture that you’ve got all these water molecules actually forming a lattice. Now, at normal temperature of life, which is 37°, there’s an average of three order molecules glued together, but they’re not stable. The interaction’s a bit like the opposing poles of a magnet. They’re not particularly strong, and so they come and go. They make and they break, and so water wanders around, but on average if you could freeze it in time, you would find there would be about three water molecules together. If you lower the temperature, that makes those interactions more stable, because there’s less vibration in the molecules, and at zero degrees, water is solid. It’s ice. And then all the water molecules are glued together and if you heat the water on the other hand, and increase the vibration activity, put more energy in there, those bonds are broken. And at 100°, there are no bonds any more, and water is a vapour, a gas.

Matt Smith

So that’s what the temperature does. It affects the bonds of the water molecule.

Nick Hoogenraad

The strength, yeah.

Matt Smith

So how much does a water molecule weigh?

Nick Hoogenraad

Oh well, we have an atomic weight, so oxygen has a atomic mass of 16 and hydrogen 1, so water has an atomic mass of 18.

Matt Smith

It’s that simple, is it?

Nick Hoogenraad

Yeah. As simple as that.

Matt Smith

And they’re all like that.

Nick Hoogenraad

They’re all like that. And these bonds, we call them hydrogen bonds because they’re between hydrogen and the oxygen, and they have one-fortieth the strength of the actual bond between the oxygen and the hydrogen in the water molecule, and depending on the temperature, as I'm talking about, the sort of living temperature, and a remarkable thing is that there is no other solvent that you could make that would support life. You need a solvent for life, because a cell must have molecules dissolved in it so that you can have interactions and reactions taking place. Life is based on a solvent and life came out of the sea, which is a solvent, it’s water too.

There are other solvents. So you can make solvents out of a number of different molecules. But no other solvent is actually a liquid, over a hundred degree range. So, we have this large space of temperature if you like, over which life is possible. That’s when water is ... that H2S, two hydrogens with a sulphur, is rotten egg gas, and it’s a gas at all of those temperatures. And you need to get to very low temperatures for them to be a solvent, so life could never be based on that.

Matt Smith

It would be a very unpleasant life.

Nick Hoogenraad

Yes, we would probably adapt our smell to be able to live with that, but the hydrogen bonds give a glue to the water molecules. It takes a lot of energy for it to go from one phase to another, as I've said, you could put a lot of heat in, to get it to go a gas. You’ve got to take a lot of heat out to go to a solid, which means that water has this magnificent property of being able to absorb heat so it can keep us at a constant temperature despite the fact that it could be 45° outside, you could be walking and you’re not forcing the temperature of the body to change because it’s actually takes a tremendous amount of heat energy to be put into the system to actually cause the temperature to actually rise. So it has this wonderful buffering capacity.

Matt Smith

So why does ice float on water then? Because it’s water on water, different states of course, but why does it float on water?

Nick Hoogenraad

Because the solid phase is actually less dense than the equus phase. It’s really important, because if ice was heavier than water, denser, then you would freeze a lake from bottom up, and then if the sun shone, you couldn’t thaw the ice, you know, the fact that the ice sits at the top means that in European countries or the more extreme temperatures like Alaska, etc, you can go through freezing thaw cycles where you can regenerate the liquid water out of the salt water, the ice.

Matt Smith

How come not all substances are water soluble?

Nick Hoogenraad

Okay, so that’s the other thing. Solubility is a critical element where water helps. So some things are soluble in water and we call those hydrophilic substances, water-loving substances, and the other molecules are water-hating or not capable of being dissolved in water, we use the Greek word hydrophobic.

Matt Smith

So something that is hydrophobic is say, something like oil?

Nick Hoogenraad

Yeah. So the hydrophilic molecules which are the amino acids, all the building blocks of the molecules of life, such as proteins, nucleic acids which are the building blocks of DNA and RNA and so forth, they all charge themselves, and so, because they are charged, they can actually interact with water and get lost in the water, if you like, so you can have a protein, and when a protein ... proteins are very complex, made of amino acids, maybe hundreds of different amino acids, and the protein actually folds so that its charged residues are on the outside and that makes them capable of being dissolved in water because instead of the water bonding to itself through hydrogen bonds, it will actually bond to the charge molecule. So the negative charge on the oxygen will interact with positive charges on the protein, and you can get very large molecules, which are polar, or hydrophilic, to actually dissolve in water.

Now, any molecule that doesn’t have charges on it, is incapable of dissolving in water. Fats, for example, fatty acids, are long chains of carbon with hydrogen – there is no charge on it except for at the very end, and so it can dissolve. So if you have a fatty acid molecule which is the basis of fats, it can have a negative charge on one end and fats are usually triglycerides, the fatty acid molecules are joined together to a glycerol, they’re charged at the end, but not at the other end, so if you now have water, these things can interact with water through their charge end and the tails can stick out of the water and so form a film of water. And then it will spread to molecular layers. And this is really important because our cells are surrounded by lipid molecules, these fat molecules, a double layer of it. And that means that the contents of the cell can’t get out of the cell to the bloodstream, and things can’t get from the bloodstream into the cell unless this membrane, this lipid membrane, has embedded in it special transporters, so only that which is allowed to go in, which the cell wants, can get in, and anything else cannot. This property of hydrophobicity, water-hating, has actually been used during evolution to create cells.

Matt Smith

You’re mentioned evolution a few times now, how important water is to life, and your eyes light up when you talk about that, so that’s clearly something that you really like. How much percentage of humans is water?

Nick Hoogenraad

Oh, it’s ... I can’t remember the exact figure but it’s certainly around 90% or more.

Matt Smith

I remember there was an episode of Star Trek where the aliens referred to the humans on the bridge as ugly bags of mostly water. Do you think it’s conceivable that if there is alien life out there, are they going to be water-based?

Nick Hoogenraad

Yes, as I said, that’s the confidence of scientists and not just my confidence. It’s just that, you know, whether Star Trek says one thing or another, it’s the case that life’s only possible if the molecules that make up a living species can communicate with one another. So they’ve got to get around and there’s got to be some connection. Like, we have blood vessels that will carry molecules like glucose and that can be sensed by tissues to see if there’s enough glucose or not and we can make insulin and stuff like that, so we can control our environment, because we have a system of connection between the different parts of our living body, and those connections require a solvent as I said, whether it’s water or something else, we need to be broad-minded about it. But the thing is, the universe is made of the same atoms, the earth is just one part of the universe.

So, we don’t know of any atoms that can actually behave like hydrogen and oxygen together that form water and make a solvent, which will allow different parts of a larger organism, a multi-cellular organism, to actually communicate with each other.

Matt Smith

So, a couple of thousand years from now, aliens are going to find that space probe, look at the side of it and go, oh yeah, we know what that is, if they’ve got a grasp of chemistry which I assume they would.

Nick Hoogenraad

Yes, I mean if they were sophisticated enough to be able to look at the space probes and capture them, they would know that there’s other life out there that’s based on the carbon atom and water. They may well have evolved into quite different shapes and different organisational structures. That’s quite possible. They may not need eyes, they may not need ears, they might have other forms of sensing and communicating, but internally you can’t build up complexity without ... when you say my eyes light up when I talk about evolution, having been a biochemist for a very, very long period of time, the tourism we understand is that I can work with the most primitive bacterium and get information from it which is relevant to humans, because we all have the same amino acids and make proteins and membranes, the same atoms, the same molecules, and the difference between a bacterium and a human is just a huge amount of complexity. Scientists cannot imagine that life could have evolved or developed in any other solvent. That’s why water’s on the side of the space ships.

Matt Smith

That was Professor Nick Hoogenraad, a molecular biologist and the Director of the La Trobe Institute for Molecular Sciences. And don’t worry, at some point soon we will have to get him back in to tell us all about carbon.

But that’s it today for the La Trobe University podcast. Don’t forget you can check out our podcast blog, that’s at podcast.blogs.latrobe.edu.au for lots of other podcasts and interviews, and we’ll also put links to the two previous discussions on water. You can also check out all the podcasts on iTunes U and this one goes in the Molecular Sciences section, with lots of other related material. Until next time, I'm Matt Smith. You have been fantastic, and thanks for listening.

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