VCE Biology Question Thread

[Poet]

In terms of Facilitated diffusion, what scenarios is ATP required for the protein carrier?

And here's my question: isn't facilitated diffusion a passive action? There's no energy expenditure, and therefore no ATP needed, right? I'm confused.

[Sine]

Facilitated diffussion is a passive process and hence does not use ATP - although it uses a protein channel to move a substance from an area of high concentration of the substance to low concentration of the substance (goes with the concentration gradient)

Active transport is an active process and does use ATP it moves substances from an area of low concentration to an area of high concentration via a protein carrier (against the concentration gradient)

[PopcornTime]

Couple of questions, if anyone could tell me if my responses are right/wrong that would be great.

What is the difference between a polypeptide chain and a protein?
- proteins are organic macromolecules which has a specific three-dimensional shape that gives it a particular function
- polypeptide chains are a series of amino acids, joined by condensation polymerisation, and do not have a particular function

In the 2006 bio exam Q1 b), it asks why beta-pleated sheets are important in the function of particular proteins. What about alpha helices?
- alpha helices allows protein to extend easily

What role do random coils play and what attributes would a protein be expected to have if they have a large number of random coils in their structure? Explain.
Not sure about this, but would it just play a role in holding a protein by wrapping around and through the secondary structures
- I assume strength

[PhoenixxFire]

What is the difference between a polypeptide chain and a protein?
- proteins are organic macromolecules which has a specific three-dimensional shape that gives it a particular function
- polypeptide chains are a series of amino acids, joined by condensation polymerisation, and do not have a particular function

This is not quite right, some proteins can be called polypeptide chains and either name is equally correct. Your definitions are otherwise correct, however some polypeptides do have a function, as they are a protein. Generally the reason for the different names is that a protein can refer to one or more polypeptide chains joined together whereas as a polypeptide chain is just one chain.

I'm not entirely sure on the details about alpha coils/beta pleated sheets/random coils. I do know that beta pleated sheets are what makes a protein 'stretchy' though (like in spider webs). And yes, the more hydrogen bonds, the stronger the protein so all of the structure makes it stronger.

[behlanarobinson]

In the 2006 bio exam Q1 b), it asks why beta-pleated sheets are important in the function of particular proteins. What about alpha helices?
- alpha helices allows protein to extend easily

What role do random coils play and what attributes would a protein be expected to have if they have a large number of random coils in their structure? Explain.
Not sure about this, but would it just play a role in holding a protein by wrapping around and through the secondary structures
- I assume strength

Regarding the question about beta pleated sheets, I took a look at the exam and its more asking why secondary structures are important - not  just specifically beta pleated sheets. You could talk about how the secondary structures contribute to the tertiary structure (thus the functioning of the protein), or how it allows the protein to stretch/contract in certain situations.

I have no clue about the random coiling though, I was never taught that and I'm pretty sure you just need to know that they exist and contribute to the folding and final shape of Tertiary/Quaternary proteins.

[Globe]

Hey guys, so I'm prepping for a bio sac coming up - and I want to make sure that I have all the molecules and their way they cross the plasma membrane correct. As far as I'm aware:

Small hydrophilic molecules - can pass through the plasma membrane
Water molecules - can pass through the plasma membrane (go through aquapores)
Hydrophobic molecules - can always diffuse through???
Charged molecules ie. ions  - Go through protein channels
Large molecules such as amino acids - Carrier proteins

Also, if it says that a molecule is "polar" and can't go through the plasma membrane, do I just assume it would require a transport protein or do I need to be more specific.

Thanks

[Poet]

Hi Globe,
Funny you and I are studying the same thing!
From my knowledge, you have everything right, and I'm pretty sure that although small polar molecules may be able to diffuse through the membrane, large polar molecules have to use transport channels (either passive or active).

Good luck on the SAC!

[PhoenixxFire]

Hey guys, so I'm prepping for a bio sac coming up - and I want to make sure that I have all the molecules and their way they cross the plasma membrane correct. As far as I'm aware:

Small hydrophilic molecules - can pass through the plasma membraneYep
Water molecules - can pass through the plasma membrane (go through aquapores) They are a small polar molecule, so they can diffuse directly across the membrane. They can also pass through aquapores, which is faster, but you do not normally need to talk about this (unless your teacher has taught you about it).
Hydrophobic molecules - can always diffuse through??? Yep. Unless they are very big (requiring bulk transport).
Charged molecules ie. ions  - Go through protein channels
Large molecules such as amino acids - Carrier proteins
The difference between channel proteins and carrier proteins is mostly in their structure rather than in the type of molecule they convey. Carrier proteins must be used for active transport, but either can be used for facilitated diffusion.

Also, if it says that a molecule is "polar" and can't go through the plasma membrane, do I just assume it would require a transport protein or do I need to be more specific. Yep, if it can't diffuse it needs a transport protein. Just saying that should be okay, however sometimes you may need to specify whether it is a protein channel or carrier protein, for example, if there is a diagram (make sure you know what each looks like) or for a molecule like glucose which normally uses a protein channel.

Thanks

[Sine]

It's aquaporins (at least that is what VCAA used the last time it was on an exam) if anyone is confused by aquapores

[Poet]

Thanks, Sine. My teacher only refers to them as porins, no 'aqua', no 'pores'. But wait, is that a different thing altogether or are they the same?

[Sine]

Thanks, Sine. My teacher only refers to them as porins, no 'aqua', no 'pores'. But wait, is that a different thing altogether or are they the same?

hmm you'd think aqua porins is a type of porin so just a subset.

[vox nihili]

Thanks, Sine. My teacher only refers to them as porins, no 'aqua', no 'pores'. But wait, is that a different thing altogether or are they the same?

A porin is actually any protein channel; whereas an aquaporin is one specific to water. This distinction is really unimportant in VCE to be perfectly honest. Frustrating, but I wouldn't worry about it too much. What Sine said above is on the money, with aquaporins obviously then being a "subset" of porins.

[DBA-144]

Does active transport use only carrier protein or only channel protein or both? I think its just carrier but im not sure.

[PolySquared]

Does active transport use only carrier protein or only channel protein or both? I think its just carrier but im not sure.

Active transport uses trans-membrane proteins (proteins that extend the thickness of the plasma membrane) to move substances against their concentration gradient. The most important pump in animal cells is called the sodium-potassium pump. The pump is an example of a carrier protein. Channel proteins are used to passively transport substances across the plasma membrane. So you're right, active transport does only use carrier proteins.

[Sine]

Does active transport use only carrier protein or only channel protein or both? I think its just carrier but im not sure.

This question is asked every year and it is sometimes quite unclear generally active transport occurs via a carrier protein but there are exceptions. For the purposes of vce it would be safe to assume that only carrier proteins are used for active transport.