We've looked at the definition of life, now let's look at the basic structure of Life. How it's made up, what are it's Fundamental units. Well, this is what you and I see on a Large scale. These are just some of the organisms that We're all familiar with. How are they actually built? What are the Building blocks? Well, of course, unsurprisingly, life is made up of Elements, the elements of the Periodic Table. And when you look at a periodic table, it looks very complex. There's well over a 100 elements there. How can all those elements come together To form life? And how can we get to the bottom of understanding which of these Elements are important? Well, it turns out that the fundamental structure of Life is really just based on a few of those elements, a very few of them. And this is a list of them here. They are in fact Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus And sulfur. Sometimes it's referred to as the word Chenops. And these are the six elements that make Up most of the compounds from which life is constructed. Throughout the elemental level, life is actually. Pretty simple. Of course it goes without saying that Other elements in the periodic table are used by life.For example, there's iron in Our red blood cells which is why we need iron in our food and there's calcium in Our bones which form the phosphate structures. That are part of all skeletons. That's why of course we drink milk to get Our calcium. So other elements are in life, but when We look at all life on Earth and we try to find the common elements that bind all Those life forms together it turns out there are very, very few of them. Just the six elements [INAUDIBLE]. That makes our task of understanding life A lot more simple. So how do we take these elements and put Them together to start to fill, form the building blocks of life? Well these Elements or atoms come together to form molecules and I've shown here an example Of one particular molecule Called Glycine, which is an amino acid, one of The building blocks of proteins. And Glycine, as you can see, is made up Of some very simple elements. There are 2 carbon atoms there. There's a nitrogen, some hydrogen, and oxygen, so you can see that even Glycine Conforms to the idea of CHNOPS. It's constructed of some of those 6 basic
Elements. And you'll notice a couple of things About this molecule. First of all, it's quite simple. And that's true of most of the molecules, which are the building blocks of life. They're very simple structures made up of a few atoms. And the other thing you'll notice is that carbon is the backbone of this particular Molecule. In fact, there are 2 carbon atoms in Glycine. And other atoms attached to those carbon Atoms. Atoms. We think of carbon as the backbone of this molecule. And this is why we refer to life on earth as being carbon based life. Because the molecules from which you and I are constructed have as their backbone Carbon. It's the common element that binds all These other elements together. So we're carbon based life. Now these molecules are very simple, as I've said, and you might think well then How can you form a much more complex organism. Well the molecules come together to make more complex molecules. I've just shown you glycine, an amino acid. If we take these amino acids and we link them together in a long chain, we end up With a protein, and a protein is essentially a long chain of amino acids. And you can think of stringing them together Like beads on a string and once They are attached together, we form these long chains and those chains can start to Do complex things like bind to other chains and fold up in particular shapes And form the complex diversity of complex molecules that make up life. Proteins, for example, make up much of your body. And here are some examples of foods that contain proteins, essential for gaining Those amino acids that your body uses to construct more complex proteins, and Other types of proteins, necessary for your body to function. And on the right day you can see some of the protein supplements that people eat In order to get hold of these amino acids that are so essential to building blocks For constructing the proteins in our cells. Of course life needs other types of molecules as well. For example, sugars, and this is an example of some sugars. And you can see on the left hand side there some healthy sugars and of course We're all familiar with some unhealthy sugars as well.
And on the right hand side there you can see a structure. Of a typical sugar. It has this ring-like structure. If you look at it it conforms again to what we've said earlier. You can see fine carbon atoms that form this ring around an oxygen and then Various other atoms attached to those to that ring of carbon atoms. Again this is. Carbon based life. It's a molecule that's constructed around the backbone of carbon with other atoms Attached to it and this particular sugar could be strung together a bit like those Amino acids in a protein to create long complex chains of sugars and that's how We end up. With these complex carbohydrates that We're familiar with in out foods. So sugars are another type of building Block that can be put together with other types of molecules to construct the Complexity of life. And it's component molecules and cells. Some of these molecules we eat, as we've just seen in proteins and sugars, and Some of these molecules we make in our body or are made by life inside the cell. This is just a rather nice example of some of the complexity that gets created Inside the cell. On the left hand side there, you can see This ring structure. Called adenine. And adenine can be transformed by adding a ribose sugar structure that you can see In the center there, to make this compound called adenosine. We can take adenosine and we can add phosphorus atoms to it and oxygen atoms, These phosphate molecules as they're called, phosphate groups. And we end up with this molecule called adenosine triphosphate. If we take adenosine triphosphate and we string it together with a variety of Other molecules, it forms a component of deoxyribonucleic acid DNA, the Information storage molecule of life. And so this is just a nice example of how The body goes from a very simple molecule, like adenine, made up of a few Carbon atoms, some nitrogen atoms and some hydrogen and strings it together, With other molecules to create something as complex as the genetic code that Allows for the transfer of material from 1 generation to another. All these reactions, these biosynthesis reactions as they are called, occur Within the cells. In all organisms on the earth, and this Is the way in which life goes from basic elements on the periodic table to very Complex molecules. Its essentially like Lego, constructing
Complex cellular structures from very simple component parts or building Blocks. Now we can't do these reactions. We can't make these molecules in a dry state. These molecules have to be moved around. They have to be added to one another. Chemical reactions have to occur whereby these molecules can grow more complex Molecules. We have to do that in a liquid as liquid Allows these molecules to move around. And on earth all life carries out these Reactions. In the liquid which is water. And that's why we say that life is also water based. It's not just carbon based, it's also water based. Water is the solvent, if you like, the solvent in which these biochemical Reactions. Can occur. So the two basic things that life needs are those six elements: Carbon, hydrogen, Nitrogen, oxygen, phosphorus and sulfur, to build the building blocks of life. And then in needs water in which these reactions can occur. And we'll look in another lecture about whether we really need these sorts of Elements, or whether alternative life forms might use different pathways But Certainly all life on earth has this common architecture of these elements and The use of liquid water as a solvent So those are the basic building blocks of Life, what have we learned in this lecture We've learned that life, is of Course, made of elements. But, it's made of very basic ones, Including carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur. We've learned that life uses other elements as well, depending on how it's Built. For example, calcium used in bones. These elements comes together to form molecules and molecules including amino Acids and sugars, the building blocks of life.These molecules come themselves, Come together to form even larger structures such as proteins and complex Sugars. And other molecules such as DNA, Deoxyribonucleic Acid. We've learned that life is a little bit Like Lego. It's built up from small components into Much more complicated ones and we've learned that life also needs water in Order to carry out These biochemical reactions, these reactions to build up From elements, to molecular building blocks, and finally, the complex Structures that we think about as life.