Granule (cell biology)
A group of leukocytes, called granulocytes, are white blood cells containing enzyme granules that play a significant role in the immune system.
Primary vesicles, also known as azurophilic granules, secrete hydrolytic enzymes including elastase, myeloperoxidase, cathepsins, and defensins that aid in pathogen distruction.
This tightly controlled process is initiated by immunological stimuli and results in the movement of granules to the cell membrane for fusion and release.
Electron tomography with three-dimensional reconstruction of platelets is notable for a significant percentage of tubular α-granules that generally lack VWF 4.
α-Granule exocytosis is evaluated primarily by plasma membrane expression of P-selectin (CD62P) by flow cytometry or estimation of the release of PF4, VWF, or other granule cargos.
Dense granules mainly contain bioactive amines (for example, serotonin and histamine), adenine nucleotides, polyphosphates, and pyrophosphates as well as high concentrations of cations, particularly calcium.
These granules derive their name from their electron-dense appearance on whole mount electron microscopy, which results from their high cation concentrations .
PDI and other platelet-borne thiol isomerases have been reported to be packaged within a non-granular compartment derived from the megakaryocyte endoplasmic reticulum (ER), which may be associated with the dense tubular system.
In the secondary phase, insulin granules are recruited from reserves deeper in the beta cell for a slower release rate.
The clatherin coating is released and the insulin secretory granules are transported across the cell via actin filaments and microtubules.
Today, the nuage is accepted to represent a characteristic, electrondense germ plasm organelle encapsulating the cytoplasmic face of the nuclear envelope of the cells destined to the germline fate.
Many germline granule components are part of the piRNA pathway and function to repress transposable elements.
Storage starch is reserved for longer periods of time and is found in non-photosynthetic tissue cells such as the roots or stem.
Stress granules are of significance for their roles in mRNA localization, cell signaling pathways, and antiviral processes.
Moreover, mutations that affect the formation or degradation of stress granules may contribute to neurodegenerative conditions such as ALS and FTLD.
