Apentix/AP Biology/Unit 1: Chemistry of Life/Question
AP Biologyhardmcq1 pt

People digest starch for energy but pass cellulose through unchanged as fiber, even though both are long glucose polymers. What accounts for the difference?

A.Starch uses alpha glycosidic linkages that fit human amylase, while cellulose uses beta linkages whose geometry no human enzyme binds
B.Cellulose contains nitrogen atoms that poison human digestive enzymes
C.Starch's beta linkages are easily hydrolyzed, while cellulose's alpha linkages are not
D.Cellulose stores far more energy per gram than starch, which overwhelms the gut

Explanation

Core Concept

Both polymers are chains of glucose joined by glycosidic bonds, but the bond geometry differs. In starch the oxygen bridge runs in the alpha configuration, producing helical chains whose shape matches the active site of human amylase. Cellulose uses beta linkages that flip every other glucose, producing straight chains whose geometry human enzymes cannot bind, so cellulose passes through undigested. Energy content per gram is essentially the same, and cellulose contains no nitrogen.

Correct Answer

AStarch uses alpha glycosidic linkages that fit human amylase, while cellulose uses beta linkages whose geometry no human enzyme binds

More Unit 1: Chemistry of Life practice questions

Try a random question →

Practice more AP Biology questions with full explanations

Practice Unit 1: Chemistry of Life Questions →