in this video, we're going to begin our discussion on the two broadest and most important structural groupings of all proteins, the fibrous and globular proteins. So in this video, we're gonna focus on the fibrous proteins, and the fibrous proteins are relatively insoluble proteins, and all that means is that they do not dissolve well and water. And so fibrous proteins are arranged and simple, long linear strands or sheets, and so usually fibers. Proteins. Onley contain one type of secondary structure, and so you'll see that they usually only contain either Alfa Hillis ease or beta sheets. But they don't have a mixture of the two, and so, because they only contain one type of secondary structure, they typically have a simple tertiary structure and fibers proteins. They function mostly as structural proteins, so they make up the structures of a lot of different things. And so what you'll see is that fibers proteins, they provide support, shape and external protection. And in our example below, we're gonna talk about three examples of fibers proteins, alfa keratin, collagen and silk LeBron. So over here on the far left, what we have is our first example, which is Alfa carrot in an Alfa carrot in is a mammalian protein that provides support and external protection. And it's found in our hair, our skin and our fingernails. And so what you'll see is that Alfa Carrolton is predominantly Alfa Helix structure. And so we have our Alfa helix here and then with the Alfa carrot in structure. What happens is to Alfa Hillis is to separate probably peptide chains. They coil up on each other to create a coiled coil and which is a type of motif. And so what you'll see is that multiple coiled coils come together to form a proto filament, and then multiple proto filaments come together to form an alfa carrot in filament. And so again, an alfa carrot in filament is predominantly made up of Alfa Helix, which is just one type of secondary structure. And you'll also see the Alfa Carrot in has this long linear type of structure. Now our second type of fibers protein is collagen, and like Alfa keratin, collagen is used to provide support. And so it's found in connective tissues such as cartilage, tendons and bones. And so what you'll see is that collagen has these three separate chains and these chains are intertwined on one another. So they have to have some turns to be able to create this turning structure that they have here now. The poly peptide chains of collagen. They're different than Alfa Carrots and because they're actually not Alfa Hillis ease and so thes chains here again, all they have are some turns to be able to, uh, intertwine the way that they do and which will also notices that collagen. It has a long, linear type of structure. So it doesn't have so many terms that create a small, spherical, globular type of shape, like what we'll see when we talk about globular proteins. Now for our last type of fiber structure, what we have is silk for Bro Owen and so, so for brown is a protein produced by insects such as spiders, spiders, and what you'll see is that it's found and spider webs and professors like to use silk for broken as a classic example of beta sheets. And what you'll see is that we've got these sheets here, these layers off anti parallel beta sheets that are all hydrogen bonded together to create the silk fibrin structure and So, uh, in our next video, we're gonna be able to get a little bit of practice on fiber proteins, and then we'll talk about the globular proteins, so I'll see you guys in those videos.
Why is collagen insoluble?
The polar side chains of its residues highly interact with water.
Its hydrophobic residues exposed on its surface do not fold away into a core in its linear structure.
Its long, linear structure increases its surface area, minimizing residue contact with water.
The lack of multiple secondary structures indirectly correlates with its lack of hydrophobic residues.
Fibrous and Globular Proteins
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So now that we know about fibers proteins, that we can talk about, our second broad group of structural proteins, the globular proteins, and we'll be able to compare and contrast fibers and globular proteins. And so unlike fibers, proteins, globular proteins are actually soluble, which means that they do dissolve well on water and globular proteins. Instead of being long and linear, they actually have compact, spherical or globular shapes. Now, we said in our previous lesson, video that fibrous proteins. They often have simple tertiary structures because they normally have on Lee one type of secondary structure but globular proteins. On the other hand, they often contained complex tertiary structures, and that's because they normally have several types of secondary structures, such as Alfa Ulysses, beta sheets, beta turns, loops and sew globular proteins. They function mostly as enzymes as well as regulatory proteins instead of functioning as structural proteins like fibrous proteins do. And so it's interesting because most the vast majority of proteins in nature are actually globular proteins, and there's only a small percentage of fibers proteins in nature. And so most of the proteins that we're gonna be talking about from here on out throughout. The rest of our course are gonna be globular proteins. And so, in our example below, we have a globular protein structures. So what you can see is that it's got a lot of turns and loops and it and it's got these Alfa Healy sees, and what you'll see is that it's got a spherical or compact shape, and that's the most important thing about globular proteins, that it doesn't have a very long or extended shape. It has a spherical, compact and globular shape, and so in our next video, we'll be able to get some practice, so I'll see you guys there.
Which of the following statements concerning protein structure is true?
All globular proteins, including myoglobin and its 8 α-helices, have quaternary structure.
Disulfide bond formation in fibrous proteins is incredibly rare due to the lack of a compact fold.
Enzyme structures tend to have significantly more beta turns than silk fibroin or α-keratin.
Hemoglobin is more soluble than collagen as a result of having a lower variety of motifs.