VCE Biology Question Thread

[Erutepa]

Where are memory b cells located?

Memory B cells will be located circulating the body through the circulatory and lymphatic system, however, will congregate and exist in large population in secondary lymphatic tissues (i.e. the lymph nodes). Interestingly (this is beyond the scope of VCE) the relative quantity of these B cells (and certain other Leukocytes) within the lymph nodes vs. circulating follows a circadian rhythm, meaning their activity as either circulating or hanging out in the lymph nodes is dependent on time of day. If interested, you can read about it here

Can someone outline the stimulus-response model in signal transduction? An example would be nice. 

The stimulus response model essentially involves:
1. the reception of a signal (by a receptor)
2. the communication/transduction of that signal
3. a cellular response (carried out by an effector)

For this course you will need to know about this model as applied to 2 scenarios: hydrophobic and hydrophilic signalling molecules.
Hydrophilic signalling molecules bind to extracellular/membrane bound receptors such to cause a conformational change in the receptor which communicates the signal into the interceullular environment. Here the signal is transduced through the activation of second messengers in a signal cascade whereby the signal in aplified as one signalling molecule may result in the production/activation of many secondary messengers. These secondary messengers activate/produce an effector molecule which then brings about a cellular response. Please note that the SD does specifically state that you don't need to know any examples of specific signal transduction mechanisms like G-protein pathways.

Hydrophobic signalling molecules cross the membrane and bind to intracellular receptors, forming a signal-receptor complex which transduces the signal through typically acting as a transciprion factor. This transription factor will alter gene expression and may, for example, involve the upregulation of a certain protein as a cellular response.

[Chocolatemilkshake]

Hi all,

Another question if anyone feels up to answering, thanks again for your help

I know that Cytotoxic T cells binds to MHC I markers. I was wondering whether they can only bind to an MHC I marker and initiate apoptosis if they have T-receptors SPECIFIC to the antigen presented on the MHC I  (hence, in order to be effective they would have to be activated by Helper T cells), or are any cytotoxic T cells able to recognise that the cell is producing non-self antigens?

[PhoenixxFire]

Hi all,

Another question if anyone feels up to answering, thanks again for your help

I know that Cytotoxic T cells binds to MHC I markers. I was wondering whether they can only bind to an MHC I marker and initiate apoptosis if they have T-receptors SPECIFIC to the antigen presented on the MHC I  (hence, in order to be effective they would have to be activated by Helper T cells), or are any cytotoxic T cells able to recognise that the cell is producing non-self antigens?

The Tc cell binds to the peptide fragment presented on the MHC1 marker, not the MHC1 marker itself (at least for the purpose of recognising infected cells). The Tc cell has to be specific to the fragment being presented (just like B cells have to be specific to the antigens they bind to). T helper cells are involved in Tc cells proliferating and differentiating, however you don't really need to talk about their role when you're talking about cell-mediated immunity.

[DBA-144]

Hi all,

Another question if anyone feels up to answering, thanks again for your help

I know that Cytotoxic T cells binds to MHC I markers. I was wondering whether they can only bind to an MHC I marker and initiate apoptosis if they have T-receptors SPECIFIC to the antigen presented on the MHC I  (hence, in order to be effective they would have to be activated by Helper T cells), or are any cytotoxic T cells able to recognise that the cell is producing non-self antigens?

Sorry if this does not quite satisfy your question, but T cytotoxic cells are part of the specific immune system and hence will specifically target particular antigens. Also, these cytotoxic T cells need to bind to specific antigens in order to be activated; therefore in order to be activated they must have the specific receptor for that antigen and hence will only target cells that present that particular antigen.

pretty sure that the cytotoxic t cell that has been selected by the antigen is the only 'type' of cytotoxic t cell that can then kill cells presenting that particular antigen. It doesn't really make sense for t helper cells to have to activate t cytotoxic cells every single time that they will be killing a cell. this would be extremely energy inefficient as cytokines need to produced, reception, transduction etc. needs to happen and then the cytotoxic t cells kills only one cell.

Not sure if I answered your questions but to sum up:
the cytotoxic t cells have to have receptors specific to that antigen to initiate apoptosis in the infected cell, if it presents foreign antigens on its MHC I. Do not need to be activated by T helper cells every single time they kill, but just need to be given the signal to proliferate once they have been selected by the antigen and come into contact with the T helper cell. No, not any random cytotoxic t cell can kill an infected cell. 

LOL beaten by a minute.
Question of my own: can someone please explain where cell mediated response takes place and the mechanism that intitiates it please?

Most importantly, I am not a bio genius, so someone else might want to confirm this, as these thoughts are my own understanding only.

[PhoenixxFire]

It doesn't really make sense for t helper cells to have to activate t cytotoxic cells every single time that they will be killing a cell. this would be extremely energy inefficient as cytokines need to produced, reception, transduction etc. needs to happen and then the cytotoxic t cells kills only one cell.

If the cell-mediated response is occurring then humoral immunity will be as well (if you've got a virus jumping between cells, there's going to be bits of that virus outside of cells). It's as part of this process that Tc cells receive the signals they need to divide and differentiate. You mentioned below about Th cells giving the signal to proliferate, so I assume that in this part you're referring to Th cells telling every individual identical Tc cell that they're allowed to kill cells - in which case you're right, only the original naive Tc cell needs that signal, once it proliferates and differentiates they'll just go off and do their thing.

Question of my own: can someone please explain where cell mediated response takes place and the mechanism that intitiates it please?

The cell-mediated response takes place everywhere that there are cells. Tc cells are always trying to bind to fragments presented on MHC1. If they do bind then they kill the cell by releasing granzymes and perforins (perforins puncture holes in the membrane allowing the granzymes to enter, granzyme cause cells to undergo apoptosis). With the correct signal from T helper cells they differentiate and proliferate and then those Tc cells with identical specificity go around continuing to attempt to bind to peptide fragments on MHC1 and killing any cells presenting fragments they can bind to.

[PhoenixxFire]

This is probably being pedantic but from my understanding, T Cells recognise the MHC and peptide fragment (ie they bind to both). This is outside of VCE, but an important component of T cell education is making sure they can bind to self (the MHC) in the thymus (cool fact- most cannot and will die!). But like I said these details are not important in VCE.

Yeah that's why I included the bit in brackets. When I did VCE I was taught about both of the receptors but it's not actually in the study design which is a bit sad because it's interesting!

For anyone curious,
Tc cells actually have two receptors (and possibly more that I don't know about), T cell receptors and CD8+ receptors.

T cell receptors are the ones that recognise peptide fragments presented on MHC1. Mature Tc cells (ie. ones that have left the thymus) should only have T cell receptors that bind to non-self peptide fragments.

CD8+ receptors bind to MHC1 itself. The CD8+ receptors on a mature Tc cell should only bind to self MHC1. Everyone's MHC1 is so unique that even MHC1 from identical twins isn't recognised as self. The CD8+ receptor causes transplants to be rejected - the Tc cell can't bind to the MHC1 so those cells are foreign. That's why people who have transplants have to take immuno suppressants.

[DBA-144]

Could someone please clear up the cell mediated process a bit more? More specifically: Where does it take place (where in the body does the t helper cell activate t cytotoxic cells?)

Also, can someone please go into more detail as to how cytotoxic t cells and t helper cells are activated? Pretty sure Th cells is not needed, so just Tc cells would be good.

Thanks.

[vox nihili]

Could someone please clear up the cell mediated process a bit more? More specifically: Where does it take place (where in the body does the t helper cell activate t cytotoxic cells?)

Also, can someone please go into more detail as to how cytotoxic t cells and t helper cells are activated? Pretty sure Th cells is not needed, so just Tc cells would be good.

Thanks.

Neither of these questions is really relevant to the VCE course, so we might steer the discussion away from there.

[Erutepa]

Could someone please clear up the cell mediated process a bit more? More specifically: Where does it take place (where in the body does the t helper cell activate t cytotoxic cells?)

Also, can someone please go into more detail as to how cytotoxic t cells and t helper cells are activated? Pretty sure Th cells is not needed, so just Tc cells would be good.

Thanks.

Like vox said, in-depth details about all this aren't really relevant, but if you want to read beyond the course to answer these questions, you might find your answers online. I often search for stuff in NCBI as they have quite a collection of exerts from different textbooks, and while some of it can be outdated,   I think it's still pretty good. Here is one chapter that you might want to read - it helped me last year when I had the same queries as you did: https://www.ncbi.nlm.nih.gov/books/NBK26827/

[Reeva.xx]

hey guys can you all please do my quick biology survey it takes 1 minute and no prior bio knowledge is needed its for a SAC and I need quite a few responses please . https://www.surveymonkey.com/r/7V3WS8L

[Joseph41]

hey guys can you all please do my quick biology survey it takes 1 minute and no prior bio knowledge is needed its for a SAC and I need quite a few responses please . https://www.surveymonkey.com/r/7V3WS8L

Hey,

Have completed the survey. I wasn't sure how to answer some of the questions, though, because I don't know what the warrior gene is!

[Reeva.xx]

Hey,

Have completed the survey. I wasn't sure how to answer some of the questions, though, because I don't know what the warrior gene is!

 haha I just realised that I forgot to add background info on that but thank you so much doing it much appreciated

[Joseph41]

 haha I just realised that I forgot to add background info on that but thank you so much doing it much appreciated

No worries at all - good luck with it!

[Sine]

hey guys can you all please do my quick biology survey it takes 1 minute and no prior bio knowledge is needed its for a SAC and I need quite a few responses please . https://www.surveymonkey.com/r/7V3WS8L

Completed survey

sidenote: I thought the background info was written well for a "lay" audience.

[AlphaZero]

hey guys can you all please do my quick biology survey it takes 1 minute and no prior bio knowledge is needed its for a SAC and I need quite a few responses please . https://www.surveymonkey.com/r/7V3WS8L

Did the survey. Some very really interesting questions there. Best of luck with your SAC