Many, many proteins are expressed on the outer surface of cells, including neuro

Question

Many, many proteins are expressed on the outer surface of cells, including neurotransmitter and hormone receptors, transport proteins, ion channels, receptors for immune cell recognition, etc. One specific protein that is expressed on skeletal muscle, adipose and liver cells is the Glut-4 glucose transporter that functions in normal glucose homeostasis. This protein is synthesized in these cell types and exists in intracellular vesicles until insulin stimulates the translocation of this protein to the cell surface. See the diagram below:

In order for a protein to be expressed on the cell surface, it must be made inside the cell transported to the plasma membrane. As you know, there are numerous steps involved in this process. Using the Glut-4 transporter as an example, list the steps involved, in order, beginning with the gene and ending at the point where Glut-4 is able to transport glucose into the cell. Don’t include the signaling molecules in the figure. (For example, “translation” is a step). I have started the answer for you…

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1. ______Transcription (DNA à mRNA)______         11. _______________________________

2. __Post-transcriptional processing of mRNA         12. _______________________________

3. _____Translation (mRNA à protein)_______        13. _______________________________

4. ________________________________                14. _______________________________

5. ________________________________                15. _______________________________

6. ________________________________                16. _______________________________

7. ________________________________                17. _______________________________

8. ________________________________                18. _______________________________

9. ________________________________                19. _______________________________

10. _______________________________                20. _______________________________

Explanation / Answer

Answer: continuing from where you left off... 4) Insulin ligands bind to RTK receptors on cell surface. 5) Dimerization and phosphorylation of the specific RTKs for insulin. 6) IRS activation 7) Glut4 vesicle exocytotic translocation towards the membrane 8) Glut4 transporter protein insertion within the membrane 9) In comes glucose.

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