What is the structural difference between starch and glycogen?

Starch and glycogen are both polysaccharides, which are complex carbohydrates composed of repeating sugar units. They serve as energy storage molecules in plants (starch) and animals (glycogen). While they have similar functions, there are some structural differences between starch and glycogen:

Branching Structure:

Starch: Starch molecules have a branched structure, consisting of two types of polysaccharides: amylose and amylopectin. Amylose is a linear chain of glucose units connected by α-1,4-glycosidic bonds. Amylopectin, on the other hand, is highly branched with both α-1,4-glycosidic bonds in the linear segments and α-1,6-glycosidic bonds at the branching points.
Glycogen: Glycogen is even more highly branched than amylopectin. It contains a central core of glycogenin protein, from which multiple chains of glucose units extend. Similar to amylopectin, glycogen also has α-1,4-glycosidic bonds in the linear segments and α-1,6-glycosidic bonds at the branching points.
Degree of Branching:

Starch: Starch molecules have fewer branches compared to glycogen. This results in a somewhat simpler structure.
Glycogen: Glycogen has a more extensive branching pattern, allowing for more efficient energy storage and retrieval. This highly branched structure permits rapid enzymatic access to the glucose units, facilitating quick energy release when needed.
Location in Organisms:

Starch: Starch is the primary storage polysaccharide in plants. It accumulates in plant cells, particularly in storage organs like seeds, tubers, and roots.
Glycogen: Glycogen is the main storage polysaccharide in animals, including humans. It is found primarily in the liver and muscle cells. The liver stores glycogen for maintaining blood glucose levels, while muscle cells store glycogen to provide a local energy source for muscle contraction.
Overall Size:

Starch: Starch molecules can be quite large, but they are generally smaller than glycogen molecules.
Glycogen: Glycogen molecules are more extensive due to their highly branched structure, which increases the number of glucose units that can be stored per molecule.
In summary, the primary differences between starch and glycogen lie in their degree of branching, location in organisms, and overall size. These structural variations reflect their specific roles in energy storage for plants and animals.