Life on Earth seems to have a number of universal properties. One of those properties is living things tend to make complex structures out of simple building blocks. In many ways life is like a child who has a set of Legos or K'nex or Lincoln Logs or whatever favorite building toy you like, and takes these Legos and makes complex structures. This is a city constructed out of Legos in Legoland. And here is a complex machine made simply out of K'nex, or made complex made by taking many, many connects and connecting them in novel ways. So the fundamental building block in either of these cases is rather simple, but they are assembled in ways to make complex, rich systems. And that's how life works. Life starts with a couple different types of basic building blocks. You could think of one as Legos, the next as K'nex, the next is your next favorite children's toy. We'll look at lipids, proteins, nucleic acids, and carbohydrates, all as examples of different building blocks that life uses to assemble cells. And the goal of this class is just to introduce some of the basic concepts here. So we'll just touch on this briefly and return back to some of these concepts in later lectures. So let me just remind you, for those of you who are not familiar with this, what things some of these building blocks are. Let's start with lipids. Lipids are, examples are fats and oils. Lipids tend to have the property that one end of the lipid is hydrophilic. It likes being in water. The other end is hydrophobic. It doesn't like interacting with water. So if I take a set of lipids, put it in water, one end of the lipid will go towards water, the other end will be away from water, and I'll end up constructing a structure like this where with this relatively simple structure I can build a membrane. So this might be a good way to build a wall. Lipids are also good ways to store energy. And humans, many creatures, store our energy in the form of fats made up of lipids. Proteins are another important tool in assembling the elements of life. The proteins on, that are used to, that are assembled are made up of 20 amino acids Proteins serve as, often as enzymes, that's one of the things they do in the body, they speed and control the reaction rates. They also do things like providing structures. And our cells assemble quite complicated proteins out of these simple amino acid building blocks. And one of the striking things about life on this planet is whether you're looking at, you know, a simple bacteria, archaea, a fungus, a dog, or a cow, they're all going to make the same, use the same Legos to build the proteins that they need to function. Its one of the many ways in which we know that life is all connected, that has all evolved from a common ancestor, because they're all using the same set of amino acids, often in the same way across quite a wide range of species to assemble proteins that carry out similar functions. Carbohydrates are another thing that we use to assemble complex structure. The building blocks of complex carbohydrates, polysaccharides are sugars. And here's an example of a set of sugars that are called pentoses because they have five carbons in a chain and by bonding in different orders, these are two structures with the same chemical properties. We can build up quite complicated polysaccharides. And finally, we turn to nucleic acids and life takes these, what are called nucleotides. A nucleotide is made of one of those five carbon sugars, one or more phosphates, and nitrogen containing base to assemble a nucleotide, a relatively simple building block. And these nucleotides are what, are assembled to make large structures, like DNA and RNA. And the DNA and RNA are the basis of our genetic code, they serve as what stores and transmits genetic information. And then code the information needed for construction of proteins. So one of the universal properties of life is that it assembles complex structures from these simple ingredients. And these complex structures are actually made from some of the most common things in the universe. You'll notice that the simple building blocks, the sugars, the nucleotides, the lipids are all assembled from hydrogen, carbon, oxygen, nitrogen, silicon, sometimes sulfur or iron. If you look at this plot, this plot shows the relative abundance of these elements in the universe versus atomic number. And you'll notice that the most familiar things, things that life are made of, are things at the top of the list. These are the common things. And you can see listed here, you know, basically the ten most common things in our universe. And that's what life is made of. This is why many of us suspect that the ability that life could evolve somewhere else is quite reasonable, because life is made up of common things. Things like gold and platinum and zirconium, or even things like lithium and beryllium, are pretty rare. And, but life doesn't use them that much. Life usually uses as the key ingredients, relatively simple components. One of the things we'll talk about later in the course when we start talking about stars is one of the great successes of twentieth century astronomy is the ability to explain this chart. The ability to explain why the universe is made mostly of hydrogen and helium, and why carbon and oxygen and nitrogen are common as products of stellar evolution. And gold is hard to make. It takes a very special environment to make gold, and that's why it's a rare and valuable quantity that, on Earth. So, now let's turn to the things that we assemble from these ingredients. And broadly speaking we can divide life, or cells into two types, prokaryotes, this are simple cells, these are things like bacteria and archaea, we've got a cell wall, no nucleus and relatively few components. This is a relatively small cell and this represents the earliest form of life. Eukaryotes have more complex structure. They have a well-defined nucleus that contains the genetic material. They also have mitochondria and other more complex structure. And animals, plants, fungi, as well as some simple things like protozoa are made of a eukaryotic life. And you'll notice, to go back to some of the things we talked about earlier, both prokaryotic life and eukaryotic life have a well defined cell boundary and all the interesting stuff inside. There's a well-defined inside and outside to all living things. Now, I want to end this lecture on a warning about how to do science, and I want to turn to actually one of my first experiences in the lab. And this was as a high school student, where I had just gone through my first few lectures and learned about prokaryotes and eukaryotes. And one of our assignments was to learn about all the parts of the cells. We were then given a slide and told to identify all the parts of all, everything we could see in that slide. And having studied all the parts of the cell, and not knowing what I had in front of me, I looked at this potato starch and tried to identify all the cell parts in the potato starch, convinced that features like this were nuclei. And much to my embarrassment, after I handed in my lab report and got it back, I discovered I was just making stuff up. And this to me was an important lesson and something that all scientists have to be mindful of when they look at their data. If you have a preconceived notion of what to expect, and what I expected was my high school biology teacher would hand us cells to classify, you'll find in your data what you expect to see. So let me end on this, and then have you turn to the questions and go back over some of the basic properties of the building blocks of life. Thanks.
