Proteins are manufactured through the "blueprints" found on DNA. After they are translated, they are moved through a system of internal membranes before being distributed throughout the rest of the cell. At some point in the process, they are modified to their functional form.
a.Describe the movement of proteins from their manufacturing point through this internal membrane system. (I think I got the general answer, but I still need a little help on this)
b.discuss the role of the following structures in the process: cell membrane, vesicles -at 2 points in the process-, ribosomes, Golgi body, and ER. (I know how all of these fit into the process except the vesicles. When do they come in?)
Thanks!
a. The movement of proteins from their manufacturing point through the internal membrane system involves a series of steps:
1. Protein Synthesis: Proteins are synthesized by ribosomes, which are located either in the cytoplasm or on the endoplasmic reticulum (ER). During translation, the genetic information on DNA is transcribed into messenger RNA (mRNA), which carries the instructions for protein synthesis.
2. Protein Translocation into the ER: If the protein is destined to be incorporated into the internal membrane system or to be secreted outside the cell, it enters the ER as it is being synthesized. Proteins that are synthesized on ribosomes attached to the ER membrane are directly translocated into the ER lumen (internal space). This translocation allows the proteins to enter the internal membrane system.
3. Protein Folding and Modifications: Within the ER lumen, proteins fold into their proper three-dimensional structures. Additionally, they may undergo various modifications, such as the formation of disulfide bonds, addition of sugar molecules (glycosylation), or trimming of specific amino acids. These modifications help proteins attain their functional form.
4. Transport from ER to Golgi Body: Once proteins are properly folded and modified in the ER, they are packaged into transport vesicles, which bud off from the ER membrane. These transport vesicles contain the proteins and move towards the Golgi body, another membrane-bound organelle.
5. Golgi Body Processing and Sorting: The Golgi body receives proteins from the ER and further modifies them. It adds additional sugar molecules, trims off unwanted segments, or adds specific chemical groups. The Golgi body also sorts the proteins into different vesicles based on their destination within or outside the cell.
6. Vesicular Transport: After processing and sorting in the Golgi body, the proteins are packaged into new vesicles, called secretory vesicles. These secretory vesicles transport the proteins to their final destinations. Some proteins are secreted outside the cell through the cell membrane, while others are distributed within the cell to specific locations.
b. In this process, the following structures play important roles:
- Cell membrane: The cell membrane serves as the boundary of the cell and helps regulate the movement of molecules in and out of the cell. It plays a role in protein secretion by allowing the release of proteins into the extracellular space.
- Vesicles: Vesicles are small membrane-bound sacs that transport substances within the cell. At two points in the protein movement process, vesicles are involved:
- Transport vesicles: They bud off from the ER membrane and carry proteins to the Golgi body.
- Secretory vesicles: These vesicles carry proteins from the Golgi body to their final destinations, either to the cell membrane for secretion or to specific intracellular locations.
- Ribosomes: Ribosomes are the cellular structures responsible for protein synthesis. They read the mRNA generated from DNA and assemble the corresponding amino acids into a polypeptide chain, forming a protein.
- Golgi body: The Golgi body, also known as the Golgi apparatus, is a stack of flattened membrane sacs. It receives proteins from the ER and modifies them further. The Golgi body also sorts proteins into different vesicles, depending on their ultimate destination. It plays a crucial role in processing and trafficking of proteins within the cell.
- Endoplasmic Reticulum (ER): The ER is a network of interconnected membranes extending throughout the cell. It has two regions: rough ER, which is studded with ribosomes, and smooth ER, which lacks ribosomes. Rough ER is involved in synthesizing and translocating proteins, while smooth ER is involved in lipid metabolism and detoxification. The proteins synthesized on rough ER ribosomes can be directly translocated into the ER lumen and are further processed and transported through the internal membrane system.