Cells synthesize and secrete the ECM molecules that surround them. Where in the cell are the components of theses ECM macromolecules synthesized?
The correct answer and explanation is:
The components of extracellular matrix (ECM) macromolecules are primarily synthesized in the rough endoplasmic reticulum (RER) and then processed and packaged in the Golgi apparatus before being secreted outside the cell.
- Rough Endoplasmic Reticulum (RER):
- The RER is the site where most ECM proteins, like collagen and fibronectin, are synthesized. Ribosomes attached to the surface of the RER translate messenger RNA (mRNA) into polypeptides that form the basic structure of ECM components.
- These polypeptides are often modified as they are synthesized. For example, the polypeptides that form collagen undergo modifications, such as the hydroxylation of proline and lysine, to create the mature collagen molecule.
- Golgi Apparatus:
- After synthesis in the RER, ECM proteins are transported to the Golgi apparatus. The Golgi is responsible for further modifying these proteins, such as adding carbohydrate chains to form glycoproteins.
- In the case of collagen, the Golgi processes the pro-collagen (an inactive precursor) by adding sugar molecules and cleaving certain peptides. This makes the protein more functional for its role in the ECM.
- Vesicle Transport:
- The modified ECM components are packaged into vesicles and transported to the cell membrane. These vesicles fuse with the plasma membrane, releasing the ECM proteins outside the cell.
- Some ECM components, like glycosaminoglycans (GAGs), are synthesized in the cytoplasm and transferred directly to the Golgi for processing and secretion.
The ECM is crucial for providing structural support, cell signaling, and tissue organization. It consists of proteins (collagen, elastin, fibronectin), proteoglycans (like heparan sulfate), and other glycoproteins that help form a scaffold for cells in tissues and organs.