Q.39. The correct combination of glycosidic linkages present in glycogen is
(A) 𝛼, 1 → 4 and 𝛼, 1 → 6
(B) 𝛼1 → 4 and 𝛽1 → 6
(C) 𝛼, 1 → 6 and 𝛽, 1 → 4
(D) 𝛼1 → 6 and 𝛽1 → 6

Core answer: The correct glycogen linkage is alpha-1,4 and alpha-1,6 (A).

Answer and core concept

• Glycogen is a branched polymer of glucose joined predominantly by alpha-1,4 glycosidic bonds along the linear chains and alpha-1,6 glycosidic bonds at branching points. This combination enables dense energy storage and rapid mobilization. The correct answer is A: alpha-1,4 and alpha-1,6.​

Explanation of each option

• Option A: Alpha-1,4 and Alpha-1,6

  • Purpose: Alpha-1,4 bonds link glucose units to form the long, unbranched portions of the glycogen chain. At branching points, alpha-1,6 bonds create new branches. This dual linkage pattern gives glycogen its highly branched, readily degradable structure.​

• Option B: Alpha-1,4 and Beta-1,6

  • Correction: Beta-1,6 bonds do not characterize glycogen branching. Glycogen branching uses alpha-1,6 bonds, not beta-1,6. This makes B incorrect for glycogen structure.​

• Option C: Alpha-1,6 and Beta-1,4

  • Correction: While alpha-1,6 bonds are involved in branching, beta-1,4 bonds are not the standard linkage in glycogen’s backbone. The predominant linkages are alpha-1,4 for the main chain and alpha-1,6 at branches, so this option misstates the backbone bond as beta-1,4.​

• Option D: Alpha-1,6 and Beta-1,6

  • Correction: Glycogen does not use beta-1,6 as a characteristic backbone or branching bond. Branching specifically involves alpha-1,6 bonds; beta-1,6 is not part of glycogen’s typical linkage pattern.​

Key structural takeaways

• Linear segments: Alpha-1,4 glycosidic bonds connect glucose residues in a straight chain. This arrangement allows tight packing of units along the glycogen molecule.​

• Branch points: Alpha-1,6 bonds create branches, typically every 8–12 glucose units, providing many ends for rapid mobilization of glucose when energy is needed.​

• Functional consequence: The combination of many short branches increases solubility and speeds access to stored glucose during glycogenolysis, which is vital for swift energy supply in animals.​

Additional context for learners

• Glycosidic bonds define the type of glycosidic linkage (alpha vs beta, and the carbon numbers). In glycogen, the alpha configuration is essential for digestibility by human enzymes like glycogen phosphorylase, while beta linkages would require different enzymes and yield different polysaccharide properties.​

• For comparison, starch (amylose and amylopectin) uses similar alpha-1,4 and alpha-1,6 linkages, but glycogen has more frequent branching, enabling even faster glucose mobilization in animals.​

Citations

• The correct linkage pattern in glycogen is alpha-1,4 for the main chain and alpha-1,6 at branching points.​

• Branching in glycogen occurs via alpha-1,6 linkages, distinguishing it from beta-linkages seen in other polymers.​

• Beta-1,6 glycosidic bonds are not characteristic of glycogen’s structure; the beta configuration is not its branching pattern.​