Fibrous and Globular Proteins - Video Tutorials & Practice Problems
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Fibrous and Globular Proteins
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In this video, we're gonna begin our discussion on the 2 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 in water. And so, fibrous proteins are arranged in simple, long, linear strands or sheets. And so usually, fibrous proteins only contain one type of secondary structure. And so you'll see that they usually only contain either alpha helices or beta sheets, but they don't have a mixture of the 2. And so, because they only contain one type of secondary structure, they typically have a simple tertiary structure. And fibrous 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 fibrous proteins, they provide support, shape, and external protection. And in our example below, we're gonna talk about 3 examples of fibrous proteins, alpha keratin, collagen, and silk fibroin. So over here on the far left, what we have is our first example which is alpha keratin. An alpha keratin 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 alpha keratin is predominantly helix structure, and so we have our alpha helix here, and then with the alpha keratin structure, what happens is 2 alpha helices, 2 separate polypeptide 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 protofilament, and then multiple protofilaments come together to form an alpha keratin filament. And so again, an alpha keratin filament is predominantly made up of alpha helix, which is just one type of secondary structure. And you'll also see that alpha keratin has this long linear type of structure. Now, our second type of fibrous protein is collagen and like alpha 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 3 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 polypeptide chains of collagen, they're different than alpha keratin because they are actually not alpha helices. And so, these chains here, again, all they have are some turns to be able to, intertwine the way that they do. And what you'll also notice is 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 febri0in. And so silk febri0in is a protein produced by insects such as spide spiders, and what you'll see is that it's found in spider webs and professors like to use silk febron as a classic example of beta sheets. And what you'll see is that we've got these sheets here, these layers of anti parallel beta sheets that are all hydrogen bonded together to create the silk fibron structure. And so, in our next video, we're gonna be able to get a little bit of practice on fibers, proteins, and then we'll talk about the globular proteins. So I'll see you guys in those videos.
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Problem
Problem
Why is collagen insoluble?
A
The polar side chains of its residues highly interact with water.
B
Its hydrophobic residues exposed on its surface do not fold away into a core in its linear structure.
C
Its long, linear structure increases its surface area, minimizing residue contact with water.
D
The lack of multiple secondary structures indirectly correlates with its lack of hydrophobic residues.
3
concept
Fibrous and Globular Proteins
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Video transcript
So now that we know about fibers proteins, 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 fibrous proteins, globular proteins are actually soluble, which means that they do dissolve well in water. And globular proteins, fibrous proteins, they often have simple tertiary structures. Now, fibrous proteins, they often have simple tertiary structures because they normally have only one type of secondary structure. But globular proteins on the other hand, they often contain complex tertiary structures and that's because they normally have several types of secondary structures such as alpha helices, beta sheets, beta turns, loops. And so 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 fibrous 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 structure. So What you can see is that it's got a lot of, turns and loops in it and it's got these alpha helices 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.
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Problem
Problem
Which of the following statements concerning protein structure is true?
A
All globular proteins, including myoglobin and its 8 α-helices, have quaternary structure.
B
Disulfide bond formation in fibrous proteins is incredibly rare due to the lack of a compact fold.
C
Enzyme structures tend to have significantly more beta turns than silk fibroin or α-keratin.
D
Hemoglobin is more soluble than collagen as a result of having a lower variety of motifs.