Overview
This lesson explains the structure of the polysaccharide cellulose, how cellulose is built from beta glucose, and how its structure enables its function in plant cell walls.
Structure of Cellulose
- Cellulose is a major component of plant cell walls.
- Unlike amylose, amylopectin, and glycogen, cellulose is a polymer of beta glucose, not alpha glucose.
- In beta glucose, the hydroxyl group on carbon 1 is positioned above the plane of the ring.
- To form glycosidic bonds between carbons 1 and 4, every second beta glucose molecule in cellulose is flipped.
- Cellulose forms an unbranched, straight-chain polysaccharide.
Arrangement in Plant Cell Walls
- Straight, unbranched cellulose chains align closely, allowing extensive hydrogen bonding between them.
- Multiple cellulose chains bonded together form microfibrils.
- Microfibrils group to form macrofibrils, which further assemble into cellulose fibers.
- These cellulose fibers create the structure of the plant cell wall.
Function of Cellulose in Plant Cells
- The large number of hydrogen bonds makes cellulose extremely strong.
- The strength of cellulose fibers allows the cell wall to resist internal pressure from water entering the cell by osmosis.
- Cellulose cell walls prevent plant cells from bursting when filled with water and help maintain cell rigidity (turgidity).
- Turgid plant cells contribute to the plant's upright structure.
- Cellulose cell walls are permeable to molecules like water.
Key Terms & Definitions
- Polysaccharide — a large carbohydrate molecule made of many monosaccharide units joined together.
- Beta glucose — a form of glucose where the hydroxyl group on carbon 1 is above the ring.
- Glycosidic bond — a type of covalent bond that joins carbohydrate molecules.
- Microfibril — a bundle of cellulose chains held together by hydrogen bonds.
- Turgid — the state of being swollen and firm due to water intake in plant cells.
Action Items / Next Steps
- Be able to draw and label a cellulose chain, showing flipped beta glucose units.
- Review how cellulose structure relates to its function in plant cell walls.