Introduction to proteins and amino acids | High school biology | Khan Academy

What we're going to do in this video is talk about proteins. Some of you all might already be familiar with them, at least in some context. If you look at any type of packaging on food, you'll oftentimes see a label that has protein listed in a certain number of grams per serving.

Some of you who might be athletically inclined might associate it with things that help you build muscle, and none of that is incorrect. But as we'll see in this video, and in many future videos, proteins are involved in almost every single biological process in every single living organism.

If we ask ourselves, what are they? Well, they're biomolecules. They're molecules found in biological systems, and they're large biomolecules. We could call them macromolecules, which is just referring to they're made up of many, many, many, many, many atoms. These right here are pictures of two different views of the chaperonin protein. This chaperonin protein is roughly eight hundred thousand times the mass of a hydrogen atom, so it's going to contain tens of thousands of atoms, which would very much make it a macromolecule.

Now one thing to be careful of, even though these are very, very large on a molecular scale, even the largest protein we know of, titan, is about one micrometer in length, and that's much larger than this chaperonin here. A micrometer is one thousandth of a millimeter, so even the largest proteins are microscopic.

Now another way to think about proteins is what they are made up of. Some proteins are made up of a single chain of something called amino acids, and things like chaperonin are made up of multiple chains of amino acids. So in a little bit, I'll show you some particular amino acids, but for now just think of them as the building blocks of proteins.

Let's say that's an amino acid, and then it will bond to another amino acid. It's not just one type of amino acid, and they can form these really, really, really long chains. Let me be very clear; this is an amino acid, and it's called that because it contains an amine group, which you don't have to worry about for now. They are the monomers that form the polymers of what's known as polypeptide chains.

So these are monomers; you build, you connect them together, and you can keep going. You can have hundreds or even thousands of these, and so this whole thing right over here, you can consider to be a polymer, and a chain of amino acids. The polymer of amino acids is known as a polypeptide. Sometimes a polypeptide chain is a protein, but sometimes a protein can be made up of multiple polypeptide chains put together.

What happens is after these amino acids connect or bond to each other, they bend and they form the shape of these proteins. You can imagine the chaperonin protein right over here; it has these chains of amino acids that bend, have a conformation that forms the shape, and that's really what gives proteins their power.

As I mentioned, proteins are involved in almost every single biological function. They play a structural role; they play a mechanical role. When your muscles contract, you have actin and myosin proteins interacting with each other so that your muscle contracts. They can act as enzymes, which we will talk about in a lot more depth in future videos. Enzymes help catalyze reactions; they help biological biochemical reactions happen in biological systems.

They can be involved with the immune system; they could be involved with signaling. They can send signals from one part of the body to another, or they can be receptors on cells that receive signals. So proteins are incredibly, incredibly important.

Now, with that out of the way, let's dig a little bit deeper into the building blocks of proteins—the monomers that build up the polymers that are polypeptides, which could be proteins or which could be used to build up proteins. What we see on the left here is the typical structure of an amino acid. Notice you see some oxygens, you see some hydrogen, some carbons, and a nitrogen.

Then bonded to this carbon right over here, you see this R, and you say, what element is that? Well, this is not an element; this is referring—this is kind of a placeholder for a side chain—which differentiates the common amino acids. You see some of the common amino acids in this diagram right over here, and you can see what the R would be for this arginine right over here. That R group would be this part.

You don't have to understand the biochemistry of it in too much detail, but you can see that they all have this top part in common, but then they all have a different R group right over here. It's different sequences of these amino acids that give us the diversity of all of the proteins that we have in biological systems and all of the various shapes.

It really, really, really, really is amazing! I mean, just going back to this picture of chaperonin, which is involved with helping other proteins get their shape—it’s chaperones, the protein folding process, so to speak. Just think about the complexity; this looks like a complex machine, but it forms naturally in biological systems.

As we explore more and more biology, we keep seeing these fascinating proteins that look like these incredible systems that really boggle the imagination.