VCE Biology Question Thread

[cosine]

Thanks guys, very helpful on this one! (I am trying to include my own understanding too, hope you enjoy xD)

1. How much do we need to know about inflammation? Would this suffice: When an invading pathogen enters the body and surpasses the first line of defence, inflammation may occur and is the process whereby blood capillaries dilate and hence blood cells rush to the infected region. Within the influx of blood, there are leucocytes that come along to fight off the infection. What else should be known?

2. Does inflammation only occur on skin surfaces? Where else can inflammation occur (i.e. inside the body like in the stomach? Idk..)

3. Is it safe to say that B cells and T cells as well as some phagocytes possess MHC class 2 markers that essentially detect the foreign material? Can it be said that the Class 2 MHC markers on these specialised cells are responsible for detecting foreign material?

4. If the question 3 is correct, is it true that class 2 MHC markers recognise class 1 markers that are found on all cells besides red blood cells?

5. If an antigen is anything that causes a specific production of antibodies, then does this mean antigens can be MHC markers? I dont know how to ask this question but what Im saying is that if B and T cells detect foreign material via their MHC class 2 markers, then does this mean that antigens are the class 1 MHC markers of foreign cells?

Many thanks in advance

[cosine]

Is divergent and branching evolution practically the same thing?

Yes, they are essentially the same thing - species evolved and diverge from ancestors and develop differences through different selection pressures.

[Biology24123]

Thanks guys, very helpful on this one! (I am trying to include my own understanding too, hope you enjoy xD)

1. How much do we need to know about inflammation? Would this suffice: When an invading pathogen enters the body and surpasses the first line of defence, inflammation may occur and is the process whereby blood capillaries dilate and hence blood cells rush to the infected region. Within the influx of blood, there are leucocytes that come along to fight off the infection. What else should be known?

2. Does inflammation only occur on skin surfaces? Where else can inflammation occur (i.e. inside the body like in the stomach? Idk..)

3. Is it safe to say that B cells and T cells as well as some phagocytes possess MHC class 2 markers that essentially detect the foreign material? Can it be said that the Class 2 MHC markers on these specialised cells are responsible for detecting foreign material?

4. If the question 3 is correct, is it true that class 2 MHC markers recognise class 1 markers that are found on all cells besides red blood cells?

5. If an antigen is anything that causes a specific production of antibodies, then does this mean antigens can be MHC markers? I dont know how to ask this question but what Im saying is that if B and T cells detect foreign material via their MHC class 2 markers, then does this mean that antigens are the class 1 MHC markers of foreign cells?

Many thanks in advance

1. Need to mention the release of histamine and that it is not specific
2. Not sure
3. MHC II is found on antigen presenting cells. MHC II only display foreign antigens. T or B cells then recognize the foreign antigen
4. MHC II don't recognise the MHC I, they display antigens
5. Antigens can be anything that are non self

[cosine]

1. Need to mention the release of histamine and that it is not specific Which cells release histamines?
2. Not sure
3. MHC II is found on antigen presenting cells. MHC II only display foreign antigens. T or B cells then recognize the foreign antigen So if MHC II is only found on APCs, then what do MHC I do? So you are saying that phagocytes put foreign material on their MHC II markers and then MHC II on B or T cells detect these?? o.O
4. MHC II don't recognise the MHC I, they display antigens
5. Antigens can be anything that are non self

[vox nihili]

1. Mast cells.

3. MHC class II molecules tell T-cells (not B-cells) that there has been an infection take place. B-cells are activated by free antigen, not antigen presented on MHC class II molecules. MHC class I molecules are expressed on all nucleated cells and serve to alert the immune system to the presence of intracellular invaders. In other words, MHC class I molecules allow cytotoxic T-cells to determine which cells to kill.

[Biology24123]

Yeah sorry, it's helper T cells that get activated by MHC II. Everything else was correct

[cosine]

I am really confused about MHC markers.. I never seem to understand what does what..

I just know MHC Class I are on all nucleated cells, and MHC Class II are on APC's, but what does what? Sorry, I just don't understand it at all.

[Biology24123]

I am really confused about MHC markers.. I never seem to understand what does what..

I just know MHC Class I are on all nucleated cells, and MHC Class II are on APC's, but what does what? Sorry, I just don't understand it at all.

It's a concept I had a lot difficulty with.

So basically,

An antigen presenting cell (macrophage, dentric cell) will engulf an antigen and display it on it's MHC II on the membrane of the cell.

A specific T helper becomes activated when it binds to the MHC II which is holding the antigen

The T helper cell can then activate cytotoxic T cells which will divide to produce active Cytotoxic T cells as well as memory cells

Now, cells than are not infected will show normal markers on the MHC I. When the cell is infected, the MHC I might show antigens that are non self

A specific cytotoxic T cell that recognises a MHC I with a foreign antigen, will destroy the cell. I don't think you need to know how antigen presentation occurs.

So the MHC II isn't recognising the MHC I. Also, T helper and cytotoxic T cells don't have MHC II, they are just receptors on the membrane of the cell

Remember, MHC I is only recognised by Cytotoxic T cells (CD8) and MHC II are only recognised by T helper cells (CD4)

Watch this video. https://www.youtube.com/watch?v=yDAGxVxY-L8

[cosine]

Okay, so I watched the video and this is my summary, here is what I still am unclear with:

The guy says that MHC Class I markers present self-antigens on their markers, and hence out own body cells will recognise them as self. When a leucocyte binds with this self-antigen, and recognises it, no reaction takes place because the MHC Class I is recognised. But what is the marker on the leucocyte called? o.O

So essentially, MHC Class I markers are the markers that determine whether a material is foreign or self? Like if the MHC I is recognised by our own leucocytes, no immune response is initiated, whereas if the MHC I is not recognised, an immune response is initiated?

[vox nihili]

Okay, so I watched the video and this is my summary, here is what I still am unclear with:

The guy says that MHC Class I markers present self-antigens on their markers, and hence out own body cells will recognise them as self. When a leucocyte binds with this self-antigen, and recognises it, no reaction takes place because the MHC Class I is recognised. But what is the marker on the leucocyte called? o.O

So essentially, MHC Class I markers are the markers that determine whether a material is foreign or self? Like if the MHC I is recognised by our own leucocytes, no immune response is initiated, whereas if the MHC I is not recognised, an immune response is initiated?

MHC molecules are surface molecules that can bind to antigens. Inside the cell, the cellular machinery puts an antigen in the middle of the MHC molecule and sends it to the surface.

To explain how T-cells bind, we need to go a little beyond the VCE course. Just to say, first of all, you only need to know that T-cells bind to MHC molecule, not how.
On the surface of T-cells are proteins called T-cell receptors (TCRs). Each TCR is specific to a particular antigen. In order to bind to an antigen, the TCR must also bind to an MHC molecule. Therefore, if the antigen isn't attached to the MHC molecule, the TCR won't bind.

As far as MHC class I and class II go:

MHC class I molecules sit on the surface of all nucleated cells. In some of them will be self molecules in others will be non-self molecules. T-cells will only bind to the ones with non-self molecules, as there are no T-cells with relevant TCRs that can bind to MHC class I molecules that present self epitopes.

MHC class II molecules only sit on the surface of antigen-presenting cells. These cells sample the environment and present the antigens they find in the environment. Therefore, binding of a T-cell to an MHC class II molecule alerts it to the presence of an infection outside of the cells, in the tissue. Binding to an MHC class I molecule, on the other hand, alerts the T-cell to an intracellular infection (i.e. a virus or something else that has actually made its way inside the cell).

[Biology24123]

Okay, so I watched the video and this is my summary, here is what I still am unclear with:

The guy says that MHC Class I markers present self-antigens on their markers, and hence out own body cells will recognise them as self. When a leucocyte binds with this self-antigen, and recognises it, no reaction takes place because the MHC Class I is recognised. But what is the marker on the leucocyte called? o.O

So essentially, MHC Class I markers are the markers that determine whether a material is foreign or self? Like if the MHC I is recognised by our own leucocytes, no immune response is initiated, whereas if the MHC I is not recognised, an immune response is initiated?

The MHC are not recognised as self, the antigens on the MHC are recognised as self or non self

[vox nihili]

The MHC are not recognised as self, the antigens on the MHC are recognised as self or non self

Just want to add to this.

Leukocytes don't actually go around the body looking for self and non-self. For instance, they don't bump into a red blood cell antigen and go "oh shit, you're actually self, no worries mate, I'll move on". Leukocytes are primed to react to things that are foreign. Something is considered "self" when leukocytes just don't react to it.

[cosine]

Just a question from an exam VCAA 2006:
 
It says that immune cells have receptors on them that distinguish the different kinds of MHC markers on all cells and hence have the ability to detect and distinguish self from non self

Could it be said that the immune cells have receptors that detect the antigens on MHC markers of other cells and if the antigen is not recognised, it is considered 'non self' material?

[vox nihili]

Just a question from an exam VCAA 2006:
 
It says that immune cells have receptors on them that distinguish the different kinds of MHC markers on all cells and hence have the ability to detect and distinguish self from non self

Could it be said that the immune cells have receptors that detect the antigens on MHC markers of other cells and if the antigen is not recognised, it is considered 'non self' material?

Hmmm, what was the answer they gave? I want to see that before I correct you, because technically what yuo're saying is wrong but I'm not sure VCE makes the distinction.

[cosine]

Hmmm, what was the answer they gave? I want to see that before I correct you, because technically what yuo're saying is wrong but I'm not sure VCE makes the distinction.

Their answer is also attached, it is the second image along with the percentage of students who answered correctly. xD