Cellulose: Study with Video Lessons, Practice Problems & Examples

Cellulose is a homopolysaccharide composed solely of D-glucose units linked by β-1,4 glycosidic bonds, forming a structural component of plant cell walls. Unlike branched polysaccharides, cellulose consists of long, unbranched chains of glucose, creating microfibrils. Most animals cannot digest cellulose due to the absence of the enzyme cellulase, which hydrolyzes these β-1,4 linkages. This indigestibility extends to cellobiose, a disaccharide formed from two glucose molecules linked by the same bond. Understanding cellulose's structure and function is crucial for studying plant biology and polysaccharide metabolism.

Cellulose

In this video, we're going to begin our lesson on cellulose. So the polysaccharide cellulose is a homopolysaccharide, which, recall from our previous lesson videos, just means that cellulose is only made up of one single type of repeating sugar unit. And that repeating sugar unit is D-glucose. And all of the D-glucose sugar units that make up the cellulose structure are covalently linked to each other via beta 1-4 glycosidic linkages. As we'll see in our course, the polysaccharides that have beta configurations in their glycosidic linkages are going to be linked to having a structural function. This will be important to keep in mind as we continue moving forward, talking about other polysaccharides.

Down below in our image, you'll see that cellulose indeed makes up the primary structure of plant cell walls. Of course, the organisms that we'll find it in are going to be plants. In terms of cellulose being a branched polysaccharide, we can say that no, it is not a branched polysaccharide. If we look down below at our image, notice we're starting with a plant at the top left, a leaf cell, and we're zooming into this leaf cell right here to get these plant cells that we see. Then zooming into the cell walls of these plant cells, notice we have this scanning electron micrograph of the plant cell walls, and you can see that it's primarily made up of cellulose fibers. The cellulose fibers are just a bunch of long cellulose microfibrils that are coming out as you see here. Notice looking at these that they're really just made up of individual glucose molecules that we have shaded here. It's just repeating, glucose molecules linked by these Beta 1-4 glycosidic linkages.

Also note that if we look at this disaccharide found within the cellulose structure, it's a disaccharide we talked about in our previous lesson videos. Two glucose molecules linked by a beta 1-4 glycosidic linkage. Is the disaccharide cellobiose? And so, you can think cellulose and cellobiose. Recall, we said that most animals cannot digest cellobiose because they don't have the enzymes that can cleave this beta 1-4 glycosidic linkage. The indigestibility of cellobiose also translates to the indigestibility of cellulose as a whole, for most animals. Again, that's because most animals are going to lack the enzyme cellulase, which is the enzyme that hydrolyzes or breaks down beta 1-4 linkages. If you don't have that enzyme to break these beta 1-4 linkages, then you won't be able to break them and you won't be able to digest them.

Really, this here concludes our lesson and introduction to cellulose, and as we move forward, we'll be able to get a little bit of practice with these concepts. So I'll see you guys in our next video.

Cellulose is composed of which of the following monosaccharides covalently bonded together in a long chain?

• A. α-glucose.
• B. Amino acids.
• C. β-glucose.
• D. Cellobiose.
• E. Peptidoglycan.
• F. Chitin.

Cellulose fibers most closely resemble _____________ in proteins.

• A. α-helices.
• B. β-sheets
• C. β-turns.
• D. Coiled-coils.

Here’s what students ask on this topic:

What is cellulose and what is its primary function in plants?

Cellulose is a homopolysaccharide composed solely of D-glucose units linked by β-1,4 glycosidic bonds. Its primary function in plants is to provide structural support. Cellulose forms long, unbranched chains that aggregate into microfibrils, which are essential components of plant cell walls. These microfibrils give the cell walls their rigidity and strength, allowing plants to maintain their shape and resist external pressures. Understanding cellulose is crucial for studying plant biology and the structural integrity of plant cells.

Why can't most animals digest cellulose?

Most animals cannot digest cellulose because they lack the enzyme cellulase, which is necessary to hydrolyze the β-1,4 glycosidic bonds between the glucose units in cellulose. Without cellulase, these β-1,4 linkages remain intact, making cellulose indigestible. This indigestibility also applies to cellobiose, a disaccharide formed from two glucose molecules linked by the same bond. As a result, cellulose passes through the digestive system of most animals without being broken down or absorbed.

What type of glycosidic linkage is found in cellulose?

Cellulose contains β-1,4 glycosidic linkages. These linkages connect the D-glucose units in a linear, unbranched chain. The β-1,4 configuration is crucial for the structural role of cellulose, as it allows the formation of strong, rigid microfibrils that contribute to the integrity of plant cell walls. This type of linkage is also why most animals cannot digest cellulose, as they lack the enzyme cellulase needed to break these bonds.

How does the structure of cellulose contribute to its function?

The structure of cellulose contributes to its function by forming long, unbranched chains of D-glucose units linked by β-1,4 glycosidic bonds. These chains aggregate into microfibrils, which are strong and rigid, providing structural support to plant cell walls. The linear arrangement and extensive hydrogen bonding between chains enhance the tensile strength and stability of the cell walls, allowing plants to maintain their shape and withstand external forces. This structural role is essential for plant growth and development.

What is the difference between cellulose and cellobiose?

Cellulose is a homopolysaccharide composed of long chains of D-glucose units linked by β-1,4 glycosidic bonds, forming a structural component of plant cell walls. Cellobiose, on the other hand, is a disaccharide consisting of two D-glucose molecules linked by a β-1,4 glycosidic bond. While cellulose is a large, complex polymer, cellobiose is a simpler molecule that serves as a building block of cellulose. Both are indigestible to most animals due to the absence of the enzyme cellulase needed to break the β-1,4 linkages.