Short Essay: “Bridges & Ferry Boats”
Ion Channels, Carrier Proteins, and Facilitated Diffusion
(25 pts)
In cell biology, comparisons can help us understand mechanism. To highlight the differences between membrane channels and transport carrier proteins, it’s been said that channels are like bridges, but carrier proteins are like ferry boats.
In your essay, explore this interesting comparison using the two SPECIFIC examples below:
Example of passive transport using a channel; the voltage-gated K+ channel
Example of passive transport using a carrier protein; the glucose transporter protein GLUT-4
In your answer, be sure to discuss the structure of the membrane protein involved, the interaction of the membrane protein with the ion or sugar it transports (for example, does the channel or carrier protein undergo a conformational change during the transport process?), and the speed and selectivity of the process in each case.
Note: You should be able to find information you need for this short essay by a) reviewing power point slides 1-18 from the ppt lecture on Membrane Transport (posted on Husky); b) Chapter 12 in the recommended text book (or comparable material in the text book of your choice); and c) many websites that compare and contrast passive transport using channel and carrier proteins.
Include a brief word about glucose transport – as we mentioned in class, there are several types of glucose transporters in cells, but for this essay you need to consider only the passive uptake of glucose by the GLUT-4 uniporter-type protein (slides 17&18).
Lastly, “carrier proteins” like GLUT-4 are also called “transporters.” You can use carrier and transporter interchangeably.
