Why can there be only one type of glycogen molecule?

Answer 1

glycogen is composed of chains of glucose molecules hooked together alpha 1,4 and branched as alpha , 1,6. This allows for only weakly branched or highly branched glycogen with the same ONE type of molecule present, glucose . Proteins , on the other hand are composed of chains and cross-linked chains of amino acids of which there are 20 naturally occurring AAs with quite different properties. You can see immediately the tremendous number of different combinations of 20 AAs that are possible. In glycogen, the position of a glucose molecule makes no difference because one glucose is like any other...In proteins substituting one amino acid for a different amino acid at a particular position will change the properties of the protein sometimes minutely other times drastically ( such as the single AA substitution of valine for a glutamic acid in a hemoglobin beta chain converts normal hemnoglobin to sickle cell hemoglobin )

Answer 2

Glycogen is a polysaccharide composed of repeating glucose units linked together. The structure of a glycogen molecule is determined by the way these glucose units are linked. Therefore, there is only one type of glycogen molecule because it is structurally uniform in terms of its glucose unit composition and linkage pattern.