Term Name:	platelet alpha granule
Synonyms:	platelet alpha-granule
Definition:	A secretory organelle found in blood platelets, which is unique in that it exhibits further compartmentalization and acquires its protein content via two distinct mechanisms: (1) biosynthesis predominantly at the megakaryocyte (MK) level (with some vestigial platelet synthesis) (e.g. platelet factor 4) and (2) endocytosis and pinocytosis at both the MK and circulating platelet levels (e.g. fibrinogen (Fg) and IgG).
Ontology:	GO: Cellular Component [GO:0031091]    QuickGO    AmiGO