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How does the Golgi apparatus modify proteins after they leave the endoplasmic reticulum?
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Golgi apparatus
A membrane-bound organelle of eukaryotic cells, the Golgi apparatus is made up of a series of flattened, stacked pouches called cisternae that function as a series of compartments that progressively refine and direct cellular products to their proper destinations. .
After proteins are synthesized in the endoplasmic reticulum and transported to the Golgi apparatus, they undergo a series of enzymatic modifications as they progress through the organelle's distinct compartmentsāthe cis, medial, and trans cisternae.12
Key modifications include:
- Glycosylation adjustments: Enzymes such as glycosidases and glycosyltransferases modify oligosaccharide chains by removing specific mannose residues and adding other sugars, such as galactose and sialic acid.12
- Chemical additions: The Golgi may add fatty acids, phosphate groups (phosphorylation), or sulfate to the molecules.2
- Proteolytic cleavage: Proteases within the Golgi or associated vesicles cut proteins at specific amino acid positions. This process often activates proteins, such as the conversion of inactive proinsulin into active insulin.12
These modifications are essential for protein stability, activity, and proper targeting to their final destinations, such as the cell membrane, lysosomes, or secretion outside the cell.312