1. Biosynthesis of a Secretory Protein The starred words are made of membranes. This means that they are all composed of phospholipids Ribosome- *Rough Endoplasmic Reticulum *Transport Vesicle *Golgi Body *Secretory Vesicle *Plasma Membrane

2. Steps in the Synthesis, Modification and Packaging of a Protein 1.Ribosome makes the polypeptide in the cytoplasm 2.Polypeptide goes through a protein import channel in the RER. 3.Within the RER, the polypeptide is cleaved, sugar added, and polypeptide folds to take a specific shape. 4.Soluble proteins are transported in a transport vesicle to the Golgi Body by exocytosis. 5.Transport vesicle with protein are moved from one area of the Golgi Body to another by endocytosis and exocytosis. 6.Protein matures, modified, packaged and made ready for use in Golgi Body and will either become a) secretory vesicleb) lysosome released from cell remain in cell

3. The next few slides illustrate the biosynthesis pathway of a secretory protein or a lysosome. Slide A shows the ribosome making the polypeptide and the polypeptide moving into the RER. Slide B shows the transport vesicle moving the protein through the Golgi Body to be modified and packaged. Slide C shows how the lysosome releases the digestive enzymes into the food vacuole. Secretory Protein Biosynthesis Animation

4. Transport vesicle buds off Secretory protein inside trans- port vesicle Glycoprotein Polypeptide Ribosome Sugar chain Rough ER 1 2 3 4 Slide A

5. Golgi apparatus Golgi apparatus “Receiving” side of Golgi apparatus Transport vesicle from ER New vesicle forming “Shipping” side of Golgi apparatus Transport vesicle from the Golgi Slide B

6. Lysosome Vesicle containing damaged mitochondrion Digestion Slide C

7. Endomembrane System The organelles involved in the biosynthesis of a protein are part of the endomembrane system. The ribosome is not because is not composed of a plasma membrane. Watch the animation to see the nature of membranes. They can fuse, break and reseal. The Nature of Membranes The membrane is involved with endocytosis and exocytosis which is how materials are moved within the cell.

8. Don’t forget: Endocytosis and Exocytosis are two means by which materials transported into or out of the cell. Below are illustrations of these processes