Iron is an essential trace element for many cellular functions. Iron uptake is accomplished with the aid of 2 proteins:
• Transferrin, a soluble protein which binds to Fe
• A Transferrin receptor, a transmembrane protein which binds the Transferrin/Fe complex. Using the table below, list each step in the Fe uptake process. Number each step and include a description of each step. Be sure to include the events of each step and any environmental conditions that are required or determine the action of the molecules involved. (15 pts.)
Note: You must use the table below for your answers. While you do not need to use every row, YOU CAN NOT CREATE MORE ROWS.
Transferrin without Fe bound does not interact with its receptor and circulates in the bloodstream until it catches an Fe ion. Once iron is bound, the iron–transferrin complex can bind to the transferrin receptor on the surface of a cell and be endocytosed. under the acidic conditions of the endosome, the transferrin releases its iron, but the transferrin remains bound to the transferrin receptor, which is recycled back to the cell surface, where it encounters the neutral pH environment of the blood.
The neutral pH causes the receptor to release the transferrin into the circulation, where it can pick up another Fe ion to repeat the cycle. The iron released in the endosome, like the LDL in Figure 15–33, moves on to lysosomes, from where it is transported into the cytosol. The system allows cells to take up iron efficiently even though the concentration of iron in the blood is extremely low. The iron bound to transferrin is concentrated at the cell surface by binding to transferrin receptors; it becomes further concentrated in clathrincoated pits, which collect the transferrin receptors.
In this way, transferrin cycles between the blood and endosomes, delivering the iron that cells need to grow.
STEP | Description of events(Include name(s) of molecules/ions, processes and required conditions) | 1 | Transferrin moves freely in the bloodstream till it binds to a Fe iron | 2 | In a neutral pH environment, transferrin binds to the Fe ion. In an acidic pH environment, transferrin doesn’t bind to the Fe ion | 3 | Fe-Transferrin complex forms and binds to the receptor on surface of cell | 4 | Adaptin binds to the receptor | 5 | Clathrin binds to adaptin which creates a coated pit and coated vesicle | 6 | Dynamin wraps itself around the pit to cause budding | 7 | The clathrin coat disappears allowing the naked vesicle to bind with the endosome | 8 | The acidic pH environment in the endosome allows the receptor to stay bound to the transferrin and leave | 9 | The neutral environment in the bloodstream allow the receptor to release the transferrin, giving it the ability to bind another Fe ion in order to repeat the cycle | 10 | The Fe Ion that is released in the endosome is transferred to lysosomes | 11 | Lysosomes finally transports Fe ion to cytosol | | | | | | | | | | |
Essay question #2
whether a medication that was applied to inhibit the protein adapter from binding to the ras pathway would help alleviate the affects of the mutant Ras (cancer). Ras is a pathway that propagates cell proliferation. It is also a G-binding protein that uses GTPase to hydrolyze itself to GDP (for inactivation )mso that the signal can be controlled. However, if the mutant Ras protein does not contain GTPase, then it cannot hydrolze itself and Ras cannot be inactivated. Cell proliferation continues and cancer can develop. Even if the medication is applied to prevent the protein adapter from binding to the Ras protein, thereby preventing the cell signal to activate the rest of the pathway, the medication only affects the part of the system that accounts for what happens to Ras BEFORE the system is affected by the mutation. That is, regardless if an extracellular signal is being inhibited by the medication, the mutant Ras itself has already been activated and can only be stopped by its own inactivation. Therefore, the medication will not work.
