Got a Biology Test back, had a question

[disturbedpanda]

Hey,

This was the question on the test:
"Explain two ways in which transport proteins move molecules across cell membranes."

So I discussed first how transport proteins can act as a tunnel, which allows certain molecules in and how they can also act as a "pump" and allow a molecule in when they are semi-open and then close the one side and open the other to allow the molecule entrance to the cell.

I got 3/5 points for my answer, can anyone suggest how I should have gone about answering it so I don't get it wrong on the midterms after Christmas break?

Thanks

[MrMistery]

well it depends on what level of detail the professor was expecting, or maybe examples.
For example, for the former type you could say that this is referred to as facilitated diffusion, and it is very fast. You also could have given examples of ion channels and aquaporins.
Your answers are right in essence (although I can't really understand your explanation of the latter type, it may be a language problem), but it really depends a lot what was expected of you.

[jonmoulton]

If, in your pump example, you are describing active transport then you need to discuss how this process is linked to a source of energy (e.g. hydrolysis of ATP or movement of a different particle "down" its concentration gradient from an area of higher concentration to an area of lower concentration). That might have been why a few points were not given -- calling the process a "pump" implies to me that it requires energy, but you did not discuss the source of that energy.

[MrMistery]

jonmoulton is right, I missed that posibility. You would have been better off contrasting the Na channel with the Glut permease for example..

[Daniel01]

I had this question on my mock exam paper but it was out of 7 marks. You needed to mention ion channels, facilatated diffusion with concentration gradient, active transport (ATP) against conc gradient, protein pores and what type of substances get let through eg. ions. I also mentioned the type of protiens used for example, intrinsic protein.