Cellulose and starch are both polymers of glucose, yet humans can digest only starch. The reason is that
- A. cellulose contains beta 1,4 linkages that human enzymes cannot hydrolyse
- B. cellulose molecules are too large to enter the gut
- C. cellulose is a protein rather than a carbohydrate
- D. starch contains no glycosidic bonds at all
Explanation
Starch is built from alpha glucose and its alpha 1,4 linkages are hydrolysed by amylase, while cellulose is built from beta glucose and its beta 1,4 linkages need cellulase, an enzyme humans do not produce. The polymer size is not the obstacle, since starch molecules are also very large. Both are carbohydrates and both contain glycosidic bonds.
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