I have two more questions.
What carries secretions for export from cell?
How do proteins and other substances get from ER to Golgi apparatus?
Sure, I can help you with both of your questions!
1. What carries secretions for export from the cell?
The secretions that need to be exported from the cell are typically carried by a structure called the Golgi apparatus. The Golgi apparatus is responsible for modifying, sorting, and packaging proteins and lipids into vesicles that can transport them to their final destinations within or outside the cell. These vesicles are known as secretory vesicles or transport vesicles.
To get a more detailed understanding of the process, you can follow these steps:
Step 1: Protein Synthesis in the Rough Endoplasmic Reticulum (ER): After being synthesized in the ribosomes attached to the rough ER, proteins undergo folding, modification, and processing.
Step 2: Budding of Transport Vesicles: Once the proteins are ready, transport vesicles bud off from the rough ER membrane, enclosing the modified proteins. These vesicles contain cargo molecules, including the secreted proteins.
Step 3: Vesicle Transport: The transport vesicles then move from the rough ER to the Golgi apparatus, which is usually located nearby in the cell. This movement occurs via a process called vesicle trafficking.
Step 4: Fusion with the Golgi Apparatus: When the transport vesicles reach the Golgi apparatus, they fuse with the Golgi membrane. This fusion allows the cargo molecules, including the secreted proteins, to enter the lumen of the Golgi apparatus.
Step 5: Processing and Packaging: Within the Golgi apparatus, the secreted proteins undergo further modification, such as protein glycosylation or addition of other chemical groups. The Golgi also sorts proteins based on their destination. Once processing and sorting are complete, the Golgi apparatus packages these proteins into new transport vesicles called secretory vesicles.
Step 6: Export from the Cell: The secretory vesicles can then be transported from the Golgi apparatus to the plasma membrane. Upon reaching the plasma membrane, the secretory vesicles fuse with it, releasing their contents to the outside of the cell through a process known as exocytosis.
2. How do proteins and other substances get from the ER to the Golgi apparatus?
The process by which proteins and other substances move from the endoplasmic reticulum (ER) to the Golgi apparatus is called anterograde transport. It involves the formation of transport vesicles that carry cargo molecules from the ER to the Golgi apparatus.
Let's break down the steps involved in this process:
Step 1: Protein Synthesis in the Rough ER: Proteins are synthesized by ribosomes attached to the rough ER membrane. As they are being synthesized, these proteins are translocated across the ER membrane and enter the ER lumen, where they undergo further processing and folding.
Step 2: Packaging of Cargo into Transport Vesicles: Once the proteins are ready to be transported, they are packaged into small transport vesicles that bud off from the rough ER membrane. These vesicles are formed by the budding process, where a portion of the ER membrane pinches off to enclose the cargo molecules.
Step 3: Vesicle Budding and Coat Protein: The budding process requires special proteins called coat proteins. These coat proteins help shape the vesicle as it buds off from the ER membrane. One type of coat protein known as COPII is specifically involved in anterograde transport from the ER to the Golgi apparatus.
Step 4: Vesicle Targeting and Microtubules: Once formed, the transport vesicles move away from the ER and travel to the Golgi apparatus. The movement is facilitated by motor proteins that "walk" along microtubules, which are part of the cytoskeleton of the cell. These microtubules act as tracks for the transport vesicles.
Step 5: Fusion with the Golgi Apparatus: When the transport vesicles reach the Golgi apparatus, they dock and fuse with the Golgi membrane. This fusion allows the cargo molecules within the vesicles to enter the lumen of the Golgi apparatus, where they can undergo further processing and sorting.
By following these steps, proteins and other substances are successfully transported from the ER to the Golgi apparatus, ensuring their proper processing, modification, and eventual distribution within or outside the cell.