VCE Biology Question Thread

[TheAspiringDoc]

Hi,
With questions related to the sequence of events in translation and transcription and that are around 3-4 marks, what kind of details does VCAA want us to include?
Thanks in advance

Process
1. Transcription
• RNA polymerase copies DNA template strand by joining
complementary nucleotides • pre-mRNA produced
• optional, depending on question: undergoes post-
transcriptional modifications – introns are removed, a poly-A tail and methyl cap are added to pre-mRNA to form mRNA
2. Translation
• mRNA travels to ribosomes
• tRNA brings a specific amino acid to the ribosome
• tRNA anticodon joins to complementary mRNA codon • an amino acid is added to the polypeptide chain

This is from the ATARNotes' VCAA approved bio definitions and processes document.

[psychologie]

why do allergic responses not produce a faster, larger response the second time they are exposed to the same allergen? (I'm assuming memory cells are produced as IgE antibodies are produced)

[vox nihili]

why do allergic responses not produce a faster, larger response the second time they are exposed to the same allergen? (I'm assuming memory cells are produced as IgE antibodies are produced)

They do?

The first exposure actually doesn't produce any allergic response at all. The second exposure does.

[TheAspiringDoc]

They do?

The first exposure actually doesn't produce any allergic response at all. The second exposure does.

Does the Rhesus factor thingo at birth count as an allergic response as parents aren't supposed to react to their babies?
If so, this occurs much more intensely upon having another baby, so if this were an allergy (pending confirmation) then this is a good example to answer the above question

[Hydroxyl]

Does the Rhesus factor thingo at birth count as an allergic response as parents aren't supposed to react to their babies?
If so, this occurs much more intensely upon having another baby, so if this were an allergy (pending confirmation) then this is a good example to answer the above question

Very interesting q!
However, I wouldn't think that would be the case. People who can't donate blood to other people are not said to be allergic to other people because they can't accept blood from them. They simply do not have the specific antigens in their own blood for the successful transfer to occur. True, allergic responses are by particles or substances that do not usually cause an immune response, such as nuts etc, but blood that cannot transfer from Person A to Person B is probably considered a normal thing.

[Atlantis]

A question to do with adaptive immunity, specifically cell-mediated immunity. I'm a bit confused so apologies if this is a silly question.

Why is it that cytotoxic T cells do not kill APCs if APCs have the foreign antigen presented on their surface?

[vox nihili]

Does the Rhesus factor thingo at birth count as an allergic response as parents aren't supposed to react to their babies?
If so, this occurs much more intensely upon having another baby, so if this were an allergy (pending confirmation) then this is a good example to answer the above question

Very interesting q!
However, I wouldn't think that would be the case. People who can't donate blood to other people are not said to be allergic to other people because they can't accept blood from them. They simply do not have the specific antigens in their own blood for the successful transfer to occur. True, allergic responses are by particles or substances that do not usually cause an immune response, such as nuts etc, but blood that cannot transfer from Person A to Person B is probably considered a normal thing.

This is a really pertinent question to VCE, because allergy is a subtle thing. Hydroxyl, you're quite right and your example is a good one. Although, it is worth saying that blood from the wrong host does generate an immune response (called a blood transfusion reaction). For instance, giving B blood to an A blood type person is extremely dangerous and will cause a potentially fatal immune response.

Allergy is not simply an immune response to something foreign. It's a specific type of immune response that involves IgE and the release of small molecule factors, such as histamine. So it is possible to react to potentially immunogenic substances in other ways that is not considered an allergy, for instance, blood transfusion reaction. Another example is coeliac disease, which is an immune response directed to a foreign substance (gluten) that some do consider an allergy, but in reality probably isn't because of the way the immune system reacts to it.

A question to do with adaptive immunity, specifically cell-mediated immunity. I'm a bit confused so apologies if this is a silly question.

Why is it that cytotoxic T cells do not kill APCs if APCs have the foreign antigen presented on their surface?

Good question.

APCs present their antigen in the context of MHC class II, whereas cytotoxic T-cells can only respond to antigen presented on MHC class I

[Ahmad_A_1999]

Hey 

Could someone please explain to me how B Cells are activated? And the role of T Helper Cells in activating the B Cells, I'm confused 

[LPadlan]

Hey 

Could someone please explain to me how B Cells are activated? And the role of T Helper Cells in activating the B Cells, I'm confused 

B-cells get activated when they bind to a specific antigen. It will then proliferate and differentiate into two different cells 1. Memory cells, basically the same as the parent cells(same antibody for the specific antigen) and plasma cells, these produce and secrete anti-bodies for the specific antigen.
T helper cells can only bind to antigens located on the MHC 2 protein in contrast to cytotoxic T cells. T helper cells activate B-cells by releasing cytokines to the B-cell that it is binded to. *Im sure these are correct, but if there is anything wrong, feel free to correct me*

[Ahmad_A_1999]

B-cells get activated when they bind to a specific antigen. It will then proliferate and differentiate into two different cells 1. Memory cells, basically the same as the parent cells(same antibody for the specific antigen) and plasma cells, these produce and secrete anti-bodies for the specific antigen.
T helper cells can only bind to antigens located on the MHC 2 protein in contrast to cytotoxic T cells. T helper cells activate B-cells by releasing cytokines to the B-cell that it is binded to. *Im sure these are correct, but if there is anything wrong, feel free to correct me*

Thanks for that! I think I've got it.

But now I'm having trouble with the cell-mediated immunity, could you help me out please, when an antigen presenting cell travels in the lymphatic system to the lymph nodes, does it present it's antigen to a T Helper Cell which then divides to produce many clones of itself, or does it present it to a T Cell, which divides into T Helper, cytotoxic and Memory T cells. 

[Deshouka]

Thanks for that! I think I've got it.

But now I'm having trouble with the cell-mediated immunity, could you help me out please, when an antigen presenting cell travels in the lymphatic system to the lymph nodes, does it present it's antigen to a T helper Cell which then divides to produce many clones of itself, or does it present it to a T Cell, which divides into T Helper, cytotoxic and Memory T cells. 

APCs present antigens to naive T cells. In the context of MHC class II, they're called naive T helper cells, which  differentiate into helper T cells and memory T cells (also called memory CD4+ T cells). However, in the context of MHC class I, they're called naive cytotoxic T cells, and can perform its function when activated. They can also differentiate into memory T cells (memory CD8+ T cells).

A question to do with adaptive immunity, specifically cell-mediated immunity. I'm a bit confused so apologies if this is a silly question.

Why is it that cytotoxic T cells do not kill APCs if APCs have the foreign antigen presented on their surface?

Interesting observation. APCs possess both MHC I and MHC II molecules. Cytotoxic T cells can and do actually kill APCs (but not often). These CD8+ cells can target a virus infected dendritic cell (an APC)  as long as it expresses the viral peptide in  the context of MHC Class I.
Obviously it is much more complex than this and it'll be detrimental if lots of APCs are killed.

Corrected some errors

[vox nihili]

APCs present antigens to naive T cells. In the context of MHC class I, they're called naive T helper cells, which  differentiate into helper T cells and memory T cells (memory CD4+ T cells). However, in the context of MHC class II, they're called naive cytotoxic T cells, and can perform its function when activated. They can also differentiate into memory T cells (memory CD8+ T cells). Memory CD4+ T cells perform the same function as helper T cells, while memory CD8+ T cells perform the same function as cytotoxic T cells.

Interesting observation. APCs possess both MHC I and MHC II molecules. Cytotoxic T cells can and do actually kill APCs (but not often). These CD8+ cells can target a virus infected dendritic cell (an APC)  as long as it expresses the viral peptide in  the context of MHC Class I.
Obviously it is much more complex than this and it'll be detrimental if lots of APCs are killed.

A couple of itty bitty details


MHC class I activates cytotoxic T-cells, and MHC class II activates T-helper cells.
CD4+ and CD8+ are not terms used in VCE; however, they are more technical descriptions of T-helper cells and cytotoxic T-cells. Saying they perform the same function implies that they're different—they're just different names for the same thing

[Apricot]

Could someone please clarify a few questions I have about adaptive immunity which I am having a bit of trouble figuring out.
1) In nature of biology, it discusses that T helper cells activate cytotoxic t cells by secreting cytokines but how does the T helper cell actually know which cytotoxic t cell to activate?
2) Can APC's present antigens to cytotoxic t cells as well or just helper t cells?
3) When t helper cell maturation occurs in the thymus, is this where they differentiate into either t helper cells or cytotoxic t cells or does the differentiation of the naive t cells into helper or cytotoxic cells occur in lymph nodes?
Apologies for the length of the questions.

[LPadlan]

Could someone please clarify a few questions I have about adaptive immunity which I am having a bit of trouble figuring out.
1) In nature of biology, it discusses that T helper cells activate cytotoxic t cells by secreting cytokines but how does the T helper cell actually know which cytotoxic t cell to activate?
2) Can APC's present antigens to cytotoxic t cells as well or just helper t cells?
3) When t helper cell maturation occurs in the thymus, is this where they differentiate into either t helper cells or cytotoxic t cells or does the differentiation of the naive t cells into helper or cytotoxic cells occur in lymph nodes?
Apologies for the length of the questions.

1. Cells involved in the specific immune response have very specific receptors for an antigen. Cytotoxic T cells that have binded to a MHC1 marker will be activated by a specific T helper cell.
 2.APCs can present to both. Antigens on MHC2 markers will be presented to T helper cells and antigens on MHC 1 markers will be presented to cytotoxic T cells.
3. I am unsure

[vox nihili]

Could someone please clarify a few questions I have about adaptive immunity which I am having a bit of trouble figuring out.
1) In nature of biology, it discusses that T helper cells activate cytotoxic t cells by secreting cytokines but how does the T helper cell actually know which cytotoxic t cell to activate?
2) Can APC's present antigens to cytotoxic t cells as well or just helper t cells?
3) When t helper cell maturation occurs in the thymus, is this where they differentiate into either t helper cells or cytotoxic t cells or does the differentiation of the naive t cells into helper or cytotoxic cells occur in lymph nodes?
Apologies for the length of the questions.

3. Thymus, but totally irrelevant to VCE.