In this video, we're going to begin our lesson on the polysaccharide starch. So, it turns out that the polysaccharide starch actually has 2 different forms, and those two different forms of the polysaccharide starch are the amylose form and the amylopectin form. And so notice here in our table for the polysaccharide column, we're showing you starch, but we're also telling you that starch has 2 different forms, the amylose form and the amylopectin form. And what you'll notice here in this table is that these first columns here that are boxed in apply to all forms of starch, amylose and amylopectin included. And so they are going to be exactly the same when it comes to all of these boxes that we have boxed in. And so really the only way that amylose and amylopectin differ from each other is in this last box over here. And so we'll talk about that when we get there. But let's go ahead and get started. So, all forms of starch, amylose and amylopectin included, are going to be homopolysaccharides, which, of course, we know from our previous lesson videos just means that it's going to be made up of just one single type of repeating sugar unit. And that repeating sugar unit is going to be D glucose for both the amylose and amylopectin form. Now all of these d glucose residues, in the starch molecules are going to be linked to each other via alpha 14glycosidic linkages, which is a little bit different than the glycosidic linkages of our previous polysaccharides that we talked about. And so in our course, the alpha configuration in the glycosidic linkage of polysaccharides is going to indicate an energy storage function. And so starch, both amylose and amylopectin, is going to serve as an energy storage molecule in plant cells. And so the organism is, of course, going to be plants. Now again, notice that for all of these boxes here, they're going to be identical for both forms of starch, amylose and amylopectin. And again, the only way that they differ is through this last box over here, the branched, box. And so, this is what distinguishes amylose from amylopectin. And so, amylose, in terms of being branched, it's actually not going to be branched. So it has absolutely no branching in the amylose form of starch. However, the amylopectin form of starch is kinda pectin. It's like pecking all over the place. So it definitely is going to be branched. So in terms of branching, we can say yes. And all of the branch points in amylopectin are going to be associated with alpha 16 glycosidic linkages, which we'll be able to visualize a little bit better in our next couple of videos when we talk about amylopectin specifically. But for now, this here concludes our table here for the two forms of starch, amylose and amylopectin. And in our next lesson video, we'll be able to talk a little bit more about amylose specifically. So I'll see you guys in that video.
2
concept
Starch
Video duration:
1m
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Video transcript
So, in this video, we can visualize how Amylose is an unbranched form of starch, just like what we said up above in our chart in our last lesson video. And so, when you take a look at this image down below, notice that it's representing the structure of amylose. And notice that amylose's structure is indeed unbranched. It's just a long linear chain here. Now, notice over here towards the end, we're showing you that amylose does actually form this helical loops, but still, the chains themselves are unbranched and there's no side chains, coming off of these, amylose, structures. And so if we take a closer look at the individual sugar units here in amylosis structure, you'll notice that all of these are just straight d glucose, molecules, and they're all linked via these alpha 14 glycosidic linkages. Now if we take a look at the disaccharide here that's found within, amylosis structure, You'll note that this is a disaccharide that we talked about in our previous lesson videos. And so we have 2 d glucose molecules that are linked via an alpha 14glycosidic linkage. This is, of course, gonna be the disaccharide maltose. And so recall from our previous lesson videos, we said that maltose is digestible to most animals. And so if maltose is digestible to most animals, that's going to translate to starch also being digestible to most animals. And so this here concludes our lesson on how amylose is an unbranched form of starch, and in our next lesson video, we'll be able to take a closer look at amylopectin. So I'll see you guys there.
3
concept
Starch
Video duration:
2m
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Video transcript
Alright. So in this video, we can visualize how amylopectin is really just a branched form of amylose. And so the amylopectin branch points are going to occur on average every 24 to 30 residues or so, and they're going to be linked via alpha 16 glycosidic linkages instead of alpha 14 glycosidic linkages. But again, this is only going to occur at the branch points. And so, if we take a look at our image down below, notice it's supposed to be representing amylopectin structure. And so notice here we have our main chain of amylopectin, and so it goes through like this and then coming off of the main chain, we have these branches that I'm highlighting here in blue And so all of these blue are branches off of the main chain. So this is really the main difference between amylopectin, which is branched, and amylose, which is up above and is not branched. And so if we zoom in here on one of the branch points, which you'll notice if we, get rid of these colors here, that the branch point right here is connected to the main chain via an alpha 16 glycosidic linkage. And, really, it's only these branch points that are gonna contain the alpha 16 linkages. And so, these circled, branch points in red down below will also have, alpha 16 glycosidic linkages. But all of the other linkages that we see are going to be alpha 14 glycosidic linkages throughout the entire thing. Again, the only ones that are gonna have alpha 16glycosidic linkages are, the branch points. And so, this here concludes our video on amylopectin structure and how it's a branch form of amylose, and we'll be able to get some practice applying the concepts that we've learned in our next couple of videos. So, I'll see you guys there.
4
Problem
Problem
Which of the following is a structural polysaccharide in plant cells?
A
Glycogen.
B
Amylose.
C
Chitin.
D
Starch.
E
Cellulose.
5
Problem
Problem
Cellulose fibers resemble ___________ in proteins; whereas amylose's structure is similar to _____________.
A
α-helices; β-sheets.
B
β-sheets; α-helices.
C
β-sheets; the hydrophobic core.
D
α-helices; β-turns.
E
β-turns; coiled-coils.
6
Problem
Problem
Cellulose, an unbranched β(1-4)-linked homopolysaccharide of D-glucose, differs from starch in that starch is:
A
A β-1,6-linked D-mannose homopolysaccharide that is branched.
B
A β-1,6-linked D-glucose homopolysaccharide that is unbranched.
C
An α-1,6-linked D-glucose homopolysaccharide that can be branched or unbranched.
D
An α-1,4-linked D-glucose homopolysaccharide that can be branched or unbranched.
E
An α-1,4-linked D-mannose homopolysaccharide that is branched.