 So here is the structure of Rubisco. It doesn't look like a Pac-Man. It doesn't look like a Rubik's Cube. It actually is a quite complex. It's quite a large enzyme complex. The reason for that is because it's actually made of 16 different proteins. So we have subunits which are grey here, so you can see the difference. And then we've got green subunits at the top and the bottom. So together these 16 proteins actually constitute 4,800 amino acids to make up this enzyme called Rubisco. Now as I indicated, this is the most abundant enzyme in the world and for us it's also the most important. So the question is, how big is Rubisco then? Well in actual fact, if you lined up 70,000 Rubisco molecules side to side here then they would actually spread one millimetre. So proteins and enzymes are actually very very small, even those which are quite large like Rubisco. Now we also talked about the catalytic sites. Now the thing about Rubisco is it doesn't have just one catalytic site, it actually has 8 for every molecule. And the reactions carried out by Rubisco is... So what happens at each of these 8 catalytic sites is Rubisco initiates the conversion of carbon dioxide into sugars. And as we know sugars comprise carbon-hydrogen oxygen. So the carbon and the oxygen in these sugars comes from the CO2 fixed by Rubisco and the hydrogen actually comes from water.