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Which type of glycosidic bond creates the branch points in glycogen?
- A Alpha-1,4 glycosidic bonds You picked ✕
- B Beta-1,6 glycosidic bonds You picked ✕
- C Alpha-1,6 glycosidic bonds You picked ✓
- D Alpha-1,3 glycosidic bonds You picked ✕
- E Beta-1,4 glycosidic bonds You picked ✕
Correct!
Incorrect
The answer is C: Alpha-1,6 glycosidic bonds
Explanation
Why C is correct
See Glycogen. Option C is correct. Glycogen is the storage form of glucose in liver and muscle. It is built from glucose units joined into straight chains by alpha-1,4 glycosidic bonds (a glycosidic bond is the link between two sugar units, and the numbers say which carbon atoms are joined). At intervals along a chain, a side chain is attached by an alpha-1,6 glycosidic bond, which joins the first carbon of one glucose to the sixth carbon of a glucose in the main chain. That creates a branch point, and repeating this gives a highly branched, tree-like molecule that packs into compact granules inside cells. The branching matters because every branch has its own free end, so many enzyme molecules can attach at once. This lets glycogen be built and broken down very quickly, which is what the body needs when blood glucose must be raised or stored fast. The branching enzyme makes the 1,6 links during glycogen synthesis, and the debranching enzyme removes them during breakdown.
- Chains: Glucose units are joined by alpha-1,4 glycosidic bonds.
- Branches: Alpha-1,6 glycosidic bonds create the branch points.
- Benefit: Many free ends let glycogen be built and broken down very quickly.
Why the other options are incorrect
- A. Alpha-1,4 glycosidic bonds: These bonds form the straight chains of glucose in glycogen, not its branch points. Most of the links in glycogen are of this kind. They would be correct for a question about the linear chains. Your answer
- B. Beta-1,6 glycosidic bonds: Glycogen does have its branches at the sixth carbon, but the bond is the alpha form, not the beta form. The alpha or beta orientation matters because it decides which enzymes can cut the bond. Your answer
- D. Alpha-1,3 glycosidic bonds: Bonds at the third carbon are found in some other polysaccharides but not as the branch points of glycogen. Glycogen branches arise from the sixth carbon of glucose. Your answer
- E. Beta-1,4 glycosidic bonds: These bonds link the glucose units of cellulose, which is built as long straight chains. Humans cannot digest them, and they are not found in glycogen. Your answer
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1
Which enzyme cleaves the α1-6 glycosidic bonds at branch points during glycogenolysis?
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2
Which feature explains why glycogen stored in skeletal muscle cannot directly supply glucose to the bloodstream?
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