Biology Unit 3 Questions Megathread

[Russ]

If I remember last year correctly (that's a huge assumption) cytosolic ribosomes are translocated to the ER when they are needed to translate a mRNA

can anyone confirm whether macrophages can / cannot ingest whole virus infected cells? or is it just Tc / NK that kill viruses ?

Macrophages would have a role in clearance of viruses but I am loathe to say they phagocytose the entire cell. They definitely phagocytose it after breakdown/apoptosis.

My textbook says that Th cells are 100% neccessary to stimulate ploliferation of B cells, but it also says T cells can only detect antigens on antigen presenting cells,

Does this mean that lone antigens / pathogens cannot cause B cells to ploliferate ?

1. B cells are antigen presenting cells
2. Yes, if a B cell encounters an antigen and does not receive T Cell help it won't proliferate.

1) exactly  how are viruses destroyed and completely eradicated from body, is it by forming antibody virus complexes or by NK / Tc cells stopping them from reproducing or both

Assuming the virus can be eradicated it's both. There are other pathways that are important as well though.

2) B cell has a similar (exactly the same) T cell, does this mean if an antigen binds with a B cell, they have to present this to the one correct Th cell and then the Th cell instructs the B cell to proliferate?

B cells do not have "exactly the same" T cells, they're very different cells. If a B cell is presenting peptide via MHCII then it needs to find any Th (there will be more than one in the body) cell that has a TCR capable of binding the MHC+peptide complex. At this point, the T cell will trigger proliferation and differentiation.

Immunity is confusing me!

Join the club lol

[WhoTookMyUsername]

haha thanks russ,

so B cells if they bind with an antigen, have to find a T cell specific for the antigen before proliferation (what does TCR stand for - something something receptor )

EDIT:

Are T cells as highly specific as B cells ?

2)
If a phagocyte presents an antigen to a T cell, how does the T cell transmit the message to a B cell (does the T cell attach to phagocyte and try to find B cell?)

[HERculina]

TCR = T-cell Receptors

[Russ]

Are T cells as highly specific as B cells ?

They are also antigen specific, yes.

2)
If a phagocyte presents an antigen to a T cell, how does the T cell transmit the message to a B cell (does the T cell attach to phagocyte and try to find B cell?)

If a macrophage/DC is presenting a peptide via MHCII, it will migrate to the lymph nodes. It will then bind a Th cell specific for that peptide and activate it. The activated T cell is now capable of activating B cells in the same lymph node.

[Kaille]

why would you remove lymph nodes from the armpit areas if you have breast cancer?

[shinny]

If the breast cancer is metastatic (i.e. has invaded into the lymphatic system and can travel through it), then you'd need to take out the primary tumour as well as the nodes to prevent existing cancer cells inside the nodes from travelling from the nodes to elsewhere and starting up the cancer again.

[Kaille]

If the breast cancer is metastatic (i.e. has invaded into the lymphatic system and can travel through it), then you'd need to take out the primary tumour as well as the nodes to prevent existing cancer cells inside the nodes from travelling from the nodes to elsewhere and starting up the cancer again.

Why would this lead to a build up of tissue fluid containing leucocytes in the arm?

Also, am i right in saying that a retrovirus has RNA as its genetic material which produces viral DNA from viral RNA. This DNA is then integrated into the host's chromasomes which causes a change in gene transcription?

[WhoTookMyUsername]

What would i ever do without you Russ ! 
+ thanks Hercules 

is the reason tyrosine is non - polar because the large variable group outways the slight polar COOH group?

Edit: I fail with acronyms, is DC dendritic cell?
Edit 2: If a B cell comes into contact with a different APC, does the B cell 'steal ' an antigen and take it to a T cell?

[shinny]

If the breast cancer is metastatic (i.e. has invaded into the lymphatic system and can travel through it), then you'd need to take out the primary tumour as well as the nodes to prevent existing cancer cells inside the nodes from travelling from the nodes to elsewhere and starting up the cancer again.

Why would this lead to a build up of tissue fluid containing leucocytes in the arm?

Also, am i right in saying that a retrovirus has RNA as its genetic material which produces viral DNA from viral RNA. This DNA is then integrated into the host's chromasomes which causes a change in gene transcription?

If you remove most of the lymph nodes from that arm, the lymphatics in that arm all have to drain through just the few remaining ones, leading to fluid congestion and accumulation. Imagine closing off all the lanes except one on a freeway - same principle here really.

And regarding retroviruses, yep, pretty much. Only other important fact to know is that this is done via reverse transcriptase, and as Russ has said many times, is basically the only exception to the Crick Central Dogma.

What would i ever do without you Russ ! 
+ thanks Hercules 

is the reason tyrosine is non - polar because the large variable group outways the slight polar COOH group?

Edit: I fail with acronyms, is DC dendritic cell?
Edit 2: If a B cell comes into contact with a different APC, does the B cell 'steal ' an antigen and take it to a T cell?

Re: edit 1, yes
Re: edit 2, why would it need to steal it? The APC can just present it to a T cell itself.

[WhoTookMyUsername]

Thanks Shinny

is the reason tyrosine is non - polar because the large variable group outways the slight polar COOH group?

Re: Re 2: if an B cell takes an antigen, then there is an increased likelyhood of one of them finding a T cell- does this occur?


Another question:
Do viruses ever go into phagocytes? How would this occur if it does? would they ingest single floating viruses?

[Russ]

is the reason tyrosine is non - polar because the large variable group outways the slight polar COOH group?

Is chemistry, but yes.

Re: Re 2: if an B cell takes an antigen, then there is an increased likelyhood of one of them finding a T cell- does this occur?

The B cell won't "steal" an antigen from an APC, no, because of the fact that APCs present degraded, linear peptides whilst the BCR doesn't bind those peptides. The BCR is just an antibody expressed on the cell membrane, so it binds a specific conformation rather than an AA sequence.

I doubt you have to know that for VCE.

Another question:
Do viruses ever go into phagocytes? How would this occur if it does? would they ingest single floating viruses?

Viruses can infect phagocytes but phagocytes don't deliberately phagocytose them

[TrueLight]

If I remember last year correctly (that's a huge assumption) cytosolic ribosomes are translocated to the ER when they are needed to translate a mRNA

can anyone confirm whether macrophages can / cannot ingest whole virus infected cells? or is it just Tc / NK that kill viruses ?

Macrophages would have a role in clearance of viruses but I am loathe to say they phagocytose the entire cell. They definitely phagocytose it after breakdown/apoptosis.

My textbook says that Th cells are 100% neccessary to stimulate ploliferation of B cells, but it also says T cells can only detect antigens on antigen presenting cells,

Does this mean that lone antigens / pathogens cannot cause B cells to ploliferate ?

1. B cells are antigen presenting cells
2. Yes, if a B cell encounters an antigen and does not receive T Cell help it won't proliferate.

1) exactly  how are viruses destroyed and completely eradicated from body, is it by forming antibody virus complexes or by NK / Tc cells stopping them from reproducing or both

Assuming the virus can be eradicated it's both. There are other pathways that are important as well though.

2) B cell has a similar (exactly the same) T cell, does this mean if an antigen binds with a B cell, they have to present this to the one correct Th cell and then the Th cell instructs the B cell to proliferate?

B cells do not have "exactly the same" T cells, they're very different cells. If a B cell is presenting peptide via MHCII then it needs to find any Th (there will be more than one in the body) cell that has a TCR capable of binding the MHC+peptide complex. At this point, the T cell will trigger proliferation and differentiation.

Immunity is confusing me!

Join the club lol

yea i would say the immune mechanisms for clearing virus infection would be NK cells, type 1 and 2 interferons, complement, CTL's and antibody protection and macrophages would play a role like Russ said either clearing dead cells or engulfing some virion particles.

you prob dont need to know this cause most antigens (the protein ones) need Th help but.... B cells ARE able to proliferate without Th cytokine help but it depends on the type of antigen that it recognises and the amount. they are called thymus independent antigens (TI-antigens).  for example LPS on gram negative bacteria, bacterial capsule polysaccharides and flagellin can induce B cell division... because the structure is repetitive it can crosslink many b cell receptors thus providing a strong enough signal to induce their proliferation.

russ answered it and i think i also answered one of your questions here http://vce.atarnotes.com/forum/index.php/topic,25843.0.html 4th post...

[amun]

i get real confused in graphs is their a particular way to understand them

[WhoTookMyUsername]

If I remember last year correctly (that's a huge assumption) cytosolic ribosomes are translocated to the ER when they are needed to translate a mRNA

can anyone confirm whether macrophages can / cannot ingest whole virus infected cells? or is it just Tc / NK that kill viruses ?

Macrophages would have a role in clearance of viruses but I am loathe to say they phagocytose the entire cell. They definitely phagocytose it after breakdown/apoptosis.

My textbook says that Th cells are 100% neccessary to stimulate ploliferation of B cells, but it also says T cells can only detect antigens on antigen presenting cells,

Does this mean that lone antigens / pathogens cannot cause B cells to ploliferate ?

1. B cells are antigen presenting cells
2. Yes, if a B cell encounters an antigen and does not receive T Cell help it won't proliferate.

1) exactly  how are viruses destroyed and completely eradicated from body, is it by forming antibody virus complexes or by NK / Tc cells stopping them from reproducing or both

Assuming the virus can be eradicated it's both. There are other pathways that are important as well though.

2) B cell has a similar (exactly the same) T cell, does this mean if an antigen binds with a B cell, they have to present this to the one correct Th cell and then the Th cell instructs the B cell to proliferate?

B cells do not have "exactly the same" T cells, they're very different cells. If a B cell is presenting peptide via MHCII then it needs to find any Th (there will be more than one in the body) cell that has a TCR capable of binding the MHC+peptide complex. At this point, the T cell will trigger proliferation and differentiation.

Immunity is confusing me!

Join the club lol

yea i would say the immune mechanisms for clearing virus infection would be NK cells, type 1 and 2 interferons, complement, CTL's and antibody protection and macrophages would play a role like Russ said either clearing dead cells or engulfing some virion particles.

you prob dont need to know this cause most antigens (the protein ones) need Th help but.... B cells ARE able to proliferate without Th cytokine help but it depends on the type of antigen that it recognises and the amount. they are called thymus independent antigens (TI-antigens).  for example LPS on gram negative bacteria, bacterial capsule polysaccharides and flagellin can induce B cell division... because the structure is repetitive it can crosslink many b cell receptors thus providing a strong enough signal to induce their proliferation.

russ answered it and i think i also answered one of your questions here http://vce.atarnotes.com/forum/index.php/topic,25843.0.html 4th post...

haha just read through that its so long -=,-= thanks tl and russ


- just to clear some things up

do T cells proliferate as soon as they come into contact with an APC or do they find a B cell first

also can Th cells proliferate into Tc cells? if a Th cell detects an antigen on an APC, do they need to come into contact with Tc cells as well?




EDIT: IN VCAA 2010 in question 6 SA part c)

http://www.vcaa.vic.edu.au/vcaa/vce/studies/biology/pastexams/2010/2010biol1-w.pdf

Is the diagram inaccurate? Compound R almost appears to be an enzyme catalysising the reaction of Q into S, but the answers suggest Compound R can be turned INTO S as in an alternative metabolc pathway, is the diagram incorrect, or is this always how metabolic pathways are drawn?

Can someone please expain or linnk to a site expalining metabolic  pathway diagrams / alternative metabolic pathway diagrams, i looked through my texts and notes, as well as online but i couldn't find anything
Thanks

[TrueLight]

"professional" antigen presenting cells - dendritic cell, macrophages, B cell

so b cells are APCs...but if the appropriate peptide is displayed on MHC and the T cell recognises it and it has appropriate co-stimulation then yes they will proliferate....DC's are the best at activating naive T cells

CD4+ T cells do not differentiate into CD8+ T cells! they are seperate types of cells

no they don't need to come into contact with Tc