Which polymer is described as linear and packed in rigid parallel fashion?

Which polymer is described as linear and packed in rigid parallel fashion?

• A. Cellulose
• B. Chitin
• C. Glycogen
• D. Amylopectin

Answer: (A)

The key idea here is how the way glucose units are linked shapes the chain and how those chains pack together. Cellulose has glucose units linked by beta-1,4 bonds. This beta linkage makes each glucose flip relative to its neighbor, producing straight, extended chains that can align in parallel with many hydrogen bonds forming between chains. Those interchain bonds pull the chains into tightly packed, crystalline microfibrils, giving cellulose a very rigid, sturdy structure in plant cell walls. Glycogen and amylopectin, on the other hand, are rich in branching and mainly use alpha linkages. The branching breaks up any long, parallel alignment, so their chains form a more branched, less rigid network rather than tightly packed parallel fibers. Chitin is linear as well and forms strong fibers, but the classic example of linear, rigidly packed polymer fibers in biological systems is cellulose, thanks to its beta-1,4 linkage and resulting parallel-chain organization.

The key idea here is how the way glucose units are linked shapes the chain and how those chains pack together. Cellulose has glucose units linked by beta-1,4 bonds. This beta linkage makes each glucose flip relative to its neighbor, producing straight, extended chains that can align in parallel with many hydrogen bonds forming between chains. Those interchain bonds pull the chains into tightly packed, crystalline microfibrils, giving cellulose a very rigid, sturdy structure in plant cell walls.

Glycogen and amylopectin, on the other hand, are rich in branching and mainly use alpha linkages. The branching breaks up any long, parallel alignment, so their chains form a more branched, less rigid network rather than tightly packed parallel fibers. Chitin is linear as well and forms strong fibers, but the classic example of linear, rigidly packed polymer fibers in biological systems is cellulose, thanks to its beta-1,4 linkage and resulting parallel-chain organization.