A Level Biology Revision "Structure and Function of Cellulose"

Summary

This video explains the structure and function of cellulose, a major component of plant cell walls. Unlike other polysaccharides like amylose and glycogen, cellulose is made up of beta-glucose molecules, where every second molecule is flipped to form glycosidic bonds. The unbranched structure of cellulose allows it to form tight, strong fibers through hydrogen bonds, creating microfibrils and macrofibrils. These fibers provide strength to the plant cell wall, making it resistant to pressure from water uptake during osmosis. This rigidity helps plant cells maintain their turgidity, contributing to the plant's upright structure.

Takeaways

• 😀 Cellulose is a major component of plant cell walls.
• 😀 Unlike amylose, amylopectin, and glycogen, cellulose is a polymer of beta glucose.
• 😀 The hydroxyl group on carbon 1 of beta glucose points above the ring, causing a structural challenge for bonding.
• 😀 Every second beta glucose molecule in cellulose flips to allow glycosidic bonds to form between carbons 1 and 4.
• 😀 Cellulose is an unbranched polysaccharide.
• 😀 The structure of cellulose allows it to form straight chains that can pack tightly together.
• 😀 Hydrogen bonds between neighboring cellulose chains make it extremely strong.
• 😀 A collection of cellulose chains forms microfibrils, which aggregate to form macrofibrils and finally cellulose fibers.
• 😀 The strength of cellulose fibers contributes to the rigidity of the plant cell wall.
• 😀 The cellulose cell wall is permeable to water, allowing it to maintain turgor pressure and resist bursting.
• 😀 Turgid plant cells, full of water, provide structural support to the plant, helping it stay upright.

Q & A

What is cellulose, and where is it found?

Cellulose is a polysaccharide made from beta-glucose molecules, and it is a major component of the cell wall in plant cells.

How does cellulose differ from other polysaccharides like amylose, amylopectin, and glycogen?

Cellulose is a polymer of beta-glucose, while amylose, amylopectin, and glycogen are polymers of alpha-glucose, which leads to different structural properties.

What is unique about the structure of beta-glucose in cellulose?

In beta-glucose, the hydroxyl group on carbon 1 points above the plane of the ring, which is different from the orientation seen in alpha-glucose.

Why does every second beta-glucose molecule in cellulose flip?

The flipping of every second beta-glucose molecule allows for the formation of glycosidic bonds between carbon 1 and carbon 4, enabling the formation of a stable cellulose chain.

What type of glycosidic bond forms between the glucose molecules in cellulose?

A beta-1,4-glycosidic bond forms between adjacent beta-glucose molecules, linking them in a linear, unbranched structure.

How does the unbranched nature of cellulose contribute to its function?

The unbranched structure of cellulose allows molecules to pack closely together, enabling the formation of strong hydrogen bonds between adjacent chains, which contributes to its strength.

What are microfibrils, and how are they related to cellulose?

Microfibrils are small fibers formed when multiple cellulose chains bundle together. These microfibrils can combine to form larger structures, such as macrofibrils and fibers, which provide structural support in plant cell walls.

What role does cellulose play in maintaining the structure of plant cells?

Cellulose provides strength and rigidity to the plant cell wall, allowing it to resist internal pressure from water intake, helping the plant cell maintain its turgidity and preventing it from bursting.

What happens when plant cells are turgid, and how does cellulose contribute to this state?

When plant cells are turgid, they are filled with water, and the contents push outward against the cellulose cell wall. The strength of cellulose prevents the cell from bursting, maintaining the cell’s rigid structure.

How does cellulose contribute to the overall function of the plant cell wall?

Cellulose contributes to the plant cell wall by providing mechanical support and strength, allowing the plant to resist external pressures and maintain its shape, while also being permeable to water and other molecules.