VCE Biology Question Thread

[cosine]

Can anyone explain the difference between the functions of the rough endoplasmic reticulum and the Golgi complex?
Does post-translational modification occur in the rough er or the Golgi body?
Where does protein packaging into vesicles occur?
What is the difference between transport and secretory vesicles?
Is it true that the endoplasmic reticulum provides an internal membrane network for the transport of substances to other organelles in the cell (other than the Golgi body)?

Any help is appreciated, guys   

The Rough Endoplasmic Reticulum are actually projections of the outer membrane of the nuclear envelope. These projections protrude out of the nucleus and span into the cytoplasm of the cell. Now, the reason that this endoplasmic reticulum is called 'rough' is because it contains many, many ribosomes that are attached to the outer most surface of the ER, hence making it appear 'rough'. Now try to link the function of ribosomes to the function of the RER. Ribosomes are the site of protein translation, so you can conclude that the RER synthesises proteins. But what would make the RER different from just free ribosomes in the cytoplasm, why would you put ribosomes on the RER if you can just synthesise proteins in the cytoplasm? Well, when a ribosome is being translated from an attached ribosome, the protein being synthesised is simultaneously entering the RER's lumen. These proteins then move off to a corner of the RER and bud off in something known as a temporary vesicle. This temporary vesicle then moves along to the Golgi Apparatus to undergo further chemical modifications and packaging. You do not need to know this, but the Golgi Apparatus has three regions of the cisternae, the cis region, the medial region and the trans region. The cis region is the side/part of the Golgi that is closest to the nucleus/RER, the medial region is the middle part and the trans region is the part closest to the cell membrane. So the temporary vesicle from the RER approaches the cis region of the Golgi and fuses with it, releasing the protein in the lumen. Here, the protein undergoes further chemical modifications, and maybe some carbohydrates are added to make the protein a glycoprotein, and then the protein buds off from the trans region in what is known as a secretory vesicle. This secretory vesicle then fuses with the cell membrane and the contents are exocytosed.

In short: RER synthesises extracellular proteins, whereas Golgi apparatus modify, package and are responsible for the transport of the proteins.

[Shax]

Hey guys, i have an issue with studying for biology.
I have just looked at my notes for the first three chapters (out of 16 chapters). They are 54 pages long, an exact copy from the textbook.
Now the thing is that although I understand the concepts and the processes really well, I am unable to regurgitate the information when I do the questions even if they are pretty simple.
Preparing notes for the chapter take a really long time that by the time I finish, I find myself a chapter behind compared to the classroom. I never look at my notes to revise the information because I feel like I am reading the textbook.
Guys, I really need your help with this. What do you suggest?

[johnhalo]

I'm having trouble distinguishing between MHC markers and antigens. My textbook doesn't make it clear enough and I'd love some assistance

Thanks

[vox nihili]

I'm having trouble distinguishing between MHC markers and antigens. My textbook doesn't make it clear enough and I'd love some assistance

Thanks

Antigens are proteins or carbohydrates produced by pathogens (i.e. invaders) that generate an immune response, whereas MHC molecules are special proteins that hold pathogens on their surface. These molecules help to stimulate a T-cell response, which can only happen if the T-cells see a pathogen in the context (in other words, with) of an MHC molecule.

[Gogo14]

There was a question in a textbook that was asking for the organelle which proteins are produced. In the answers it says ribosome, but thats not an organelle. So what should I do if I come across a q like that in the exam? Or do they not ask questions like that?

[vox nihili]

There was a question in a textbook that was asking for the organelle which proteins are produced. In the answers it says ribosome, but thats not an organelle. So what should I do if I come across a q like that in the exam? Or do they not ask questions like that?

In VCE, a ribosome would be accepted as an organelle. You could also, however, say rough endoplasmic reticulum here too.

[Jay.C]

There was a question in a textbook that was asking for the organelle which proteins are produced. In the answers it says ribosome, but thats not an organelle. So what should I do if I come across a q like that in the exam? Or do they not ask questions like that?

Yeah it's highly likely they won't ask a question like that in the exam because protein synthesis cannot merely be explained under one organelle. They are however likely to ask about the process of protein synthesis, e.g. How/where does translation/transcription, so make sure you know the process of protein synthesis.

[vox nihili]

Yeah it's highly likely they won't ask a question like that in the exam because protein synthesis cannot merely be explained under one organelle. They are however likely to ask about the process of protein synthesis, e.g. How/where does translation/transcription, so make sure you know the process of protein synthesis.

Be careful when you differentiate between protein synthesis and gene expression. Protein synthesis is translation, not the stuff that precedes it.

[johnhalo]

In addition, is there any difference between a 'self' antigen and a MHC Marker?

[cosine]

In addition, is there any difference between a 'self' antigen and a MHC Marker?

Yes, MHC markers are the protein complexes that actually 'carry' the self antigen and present them to other cells. Whereas the 'self' antigen is the actual molecule that 'labels' the identity of the cell.

[vox nihili]

In addition, is there any difference between a 'self' antigen and a MHC Marker?

Yes, MHC markers are the protein complexes that actually 'carry' the self antigen and present them to other cells. Whereas the 'self' antigen is the actual molecule that 'labels' the identity of the cell.

It's worth adding to this that the immune system, when it's behaving properly, doesn't respond to self-antigens at all. Indeed, it can't even recognise them. If the immune system recognises something, it will respond to it. So self molecules are basically just those molecules to which the immune system can't respond because they don't have receptors for them.

[Shax]

If the plasma membrane is amphipathic, then how can lipid-soluble molecules dissolve in the lipid bilayer? They have to cross the hydrophilic phosphate heads first in order to get to the fatty acid tails. It is also the same from the intercellular side of the membrane; they are going to get repelled by the inner hydrophilic heads as well.
Guys, how can any substance cross the plasma membrane at all (unless that same substance is also amphipathic)? And why do small molecules, like water, cross the membrane freely? Isn't water a polar substance?!!

[Photon]

Can someone tell me how many hydrogen ions are used to create 1 atp molecule in the light-dependent stage of photosynthesis? Thanks

[TheAspiringDoc]

Can someone tell me how many hydrogen ions are used to create 1 atp molecule in the light-dependent stage of photosynthesis? Thanks

12H2O -> 24H + 18ATP I think. Then the 24H+ will be loaded onto NADP+ carriers  and in the LI stages the 18ATP + the 24NADPH will be of assistance in creating the glucose (simplified but that's VCE 4u)

[Photon]

12H2O -> 24H + 18ATP I think. Then the 24H+ will be loaded onto NADP+ carriers  and in the LI stages the 18ATP + the 24NADPH will be of assistance in creating the glucose (simplified but that's VCE 4u)

Thank you but I wasn't really asking for the process. Sorry if my wording was a little bit off but I wanted to know how many protons are used to make a single ATP. As in when the hydrogen ions pass through ATP synthase how many need to go through to form one ATP molecule. So the ratio would either be 18:24 or 18:12. so 3 ATP : 4 H+ ions or 3 ATP : 2 H+ ions. Do all the hydrogen ions pass through the ATP synthase? Including the 12 that are left behind? If so then we would have 3 ATP molecules for every 4 hydrogen ions or 1 ATP for 0.75 of a proton which sucks really :/