Storage Granules Definition
- Storage granules are membrane-bounded vesicles containing condensed materials.
- They are also known as zymogen granules or condensing vacuoles.
- Storage granules are an important component of metabolism in many organisms spanning the bacterial, eukaryotes and archaeal domains.
- These granules are the parts of the cell that store the cell’s energy reserves as well as other important metabolites.
Figure: Diagram of Storage Granules. Image Source: Slide Player
Structure of Storage Granules
- Storage granules are simple small organelles, bounded by a lipid bilayer membrane. On the inside of the membrane, it contains the stored material.
- Different materials may be stored for different purposes by storage granules depending upon the location where they are found. For example, mast‐cell storage granules contain histamine, while those of pancreatic B cells contain insulin.
- Generally, storage granules are polyphosphate bodies that contain a large amount of phosphorous and oxygen. They also have increased levels of iron and magnesium.
- Primary lysosomes which are also called storage granules are newly formed organelles bounded by a single membrane and typically having a diameter of 100 nm. They contain the degradative enzymes which have not participated in any digestive process.
Functions of Storage Granules
- Granules found in plastids or in the cytoplasm, assumed to be food reserves, often of glycogen or other carbohydrate polymers.
- In prokaryotes, nutrients and reserves may be stored in the cytoplasm in the form of glycogen, lipids, polyphosphate, or in some cases, sulfur or nitrogen.
- Sulfur granules are especially common in bacteria that use hydrogen sulfide as an electron source.
- The lysosomes of plant cells are membrane-bounded storage granules containing hydrolytic digestive enzymes, e.g., large vacuoles of parenchymatous cells of corn seedlings, protein or aleurone bodies and starch granules of cereal and other seeds.
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- Toso, D. B., Henstra, A. M., Gunsalus, R. P., & Zhou, Z. H. (2011). Structural, mass and elemental analyses of storage granules in methanogenic archaeal cells. Environmental microbiology, 13(9), 2587-99.