Which of the following statements about hydrogen bonding in glycogen and cellulo

Question

Which of the following statements about hydrogen bonding in glycogen and cellulose is true?

A) Glycogen forms more internal H-bonds than cellulose.
B) Extensive internal hydrogen bonding makes cellulose more water soluble than glycogen.
C) Extensive hydrogen bonding with water makes cellulose more soluble than glycogen.
D) Glycogen primarily forms hydrogen bonds within a single chain.
E) The hydrogen bonding in cellulose favors a helical conformation.

D is the correct answer. However, according to Lehninger 6th, glycogen is a tightly coiled helix that is stabilized by INTERchain hydrogen bonds (page 258). Since cellulose is the more stable molecule that forms both inter and intrachain hydrogen bonds, why does the correct answer basically state that glycogen also forms INTRAchain hydrogen bonds?

Explanation / Answer

Ans. Cellulose: Cellulose is a linear, unbranched homopolymer of -D-glucose linked together by (14) glycosidic bond. A single linear cellulose molecule may consist of around 2000-3000 glucose residues. Several linear cellulose molecules are aligned parallel to each other to form a cellulose fibre (or, simply called fibre). The fibre has numerous inter-strand (between two cellulose strands/molecules) H-bonds.

# Glycogen: A single glycogen molecule may have around 106 -D-glucose linked together by (14) glycosidic bond in the main chain. The short branches of glucose molecules are linked to the main chain by (16) glycosidic bond.

There is formation of intra-strand (within one glycogen molecule/polymer/strand) H-bonds that stabilizes the coiled structure.

# So, correct option is- D. Glycogen primarily forms (intra-strand) H-bonds within a single chain.

# Note that there is no intra-chain H-bonds within a single chain of cellulose because each cellulose molecule (each single polymer) is LINEAR and UNBRANCHED. However, inter-chain H-bonds form only between two cellulose molecules to from a fibre.

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