VCE Biology Question Thread

[sunshine98]

do we need to know about antigenic variation ?

[BakedDwarf]

Do we need to know HOW cholesterol maintains the fluidity of the plasma membrane?

[paper-back]

Why can't monosaccharides diffuse through the plasma membrane, when amino acids and water molecules can? Aren't they all hydrophillic?

On page 13 VCAA Exam 1 2007, they've labelled a "cell of the immune system" as having an antigen. I thought an antigen was a foreign body that induces an immune response. Why do immune cells have self and non-self antigens then?

[cosine]

Why can't monosaccharides diffuse through the plasma membrane, when amino acids and water molecules can? Aren't they all hydrophillic?

On page 13 VCAA Exam 1 2007, they've labelled a "cell of the immune system" as having an antigen. I thought an antigen was a foreign body that induces an immune response. Why do immune cells have self and non-self antigens then?

Every cell in our body displays self antigens on MHC Class I markers. Its like these markers display antigens on their surface so that they have a ticket, whenever a security guard passes (Cytotoxic T-Cell), they can present this self antigen and will be safe. If a cell of the body is infected by a virus, the virus incorporates it's nucleic acid onto the genome of the cell and produces non-self antigens to display onto the MHC I marker of the infected cell. Because this cell now has non-self antigens on it's surface, whenever the security guard comes by, it will be detected and thrown out of the venue (our body). Hope that makes sense.

Also note that because bacterial cells do not have MHC markers, they get detected by phagocytes through phagocytic receptors and are engulfed. So these bacterial antigens are obviously non-self, meaning the phagocytes recognise them as being different, foreign, and engulfs them.

[vox nihili]

Why can't monosaccharides diffuse through the plasma membrane, when amino acids and water molecules can? Aren't they all hydrophillic?

On page 13 VCAA Exam 1 2007, they've labelled a "cell of the immune system" as having an antigen. I thought an antigen was a foreign body that induces an immune response. Why do immune cells have self and non-self antigens then?

To your first question:

some amino acids have highly hydrophobic regions so they can use those to dissolve through the membrane. Phenylalanine ,for instance, has a massive hydrophobic region that makes the molecule essentially hydrophobic. Some amino acids do actually require transport across the membrane though.
Water molecules are really small, so despite their polarity they can just sneak through the fatty acid tails.
Monosaccharides, on the other hand, are pretty chunky and pretty polar, so they can't get through

To the second:

You're quite right in everything you've said there. They've called it an antigen when what they're really referring to is a surface molecule. In reality, if that immune cell were dumped in another animal, then that same marker would be antigenic.

[cosine]

Few questions:

1. Is fever always associated with inflammation in VCE Bio?

2. If so/not, can you explain why, please?

3. I know that macrophages release interleukins to stimulate the hypothalamus of the brain to increase the body temperature, in hope to reduce pathogenic metabolism and activity, is there any more information needed for VCE bio about fever?

4. How much do we need to know about mast cells? My textbook only says that they release histamines to a). vasodilate blood vessels allowing an influx of white blood cells to the scene of infection and b). releasing histamines to increase blood vessel permeability to allow certain whiteblood cells to squeeze through and fight off the infection. Do we need to know about what sort of antibodies they exhibit on their surfaces? If so, which antibodies are they?

5. Are mast cells embedded or are they free cells?

6. Do we need to know the different types of antibodies?

7. If antibodies have a y structure and have two antigen-binding sites, can both of these sites bind on two of the same antigens on the same pathogen?

8. How much do we need to know about inflammation, besides that mast cells releasing histamines for specific responses and there will be redness, swelling and pain at the site of infection?

9. Must we know about the lymphatic system including the vessels and direction flow ?

10. If B and T cells are both produced from stem cells in the bone marrow, and B cells mature in the bone marrow whereas T cells migrate to the thymus to mature, where are they kept in storage? Is it both in the spleen and lymph nodes or?

Many thanks.

[vox nihili]

Few questions:

1. Is fever always associated with inflammation in VCE Bio?

2. If so/not, can you explain why, please?

3. I know that macrophages release interleukins to stimulate the hypothalamus of the brain to increase the body temperature, in hope to reduce pathogenic metabolism and activity, is there any more information needed for VCE bio about fever?

4. How much do we need to know about mast cells? My textbook only says that they release histamines to a). vasodilate blood vessels allowing an influx of white blood cells to the scene of infection and b). releasing histamines to increase blood vessel permeability to allow certain whiteblood cells to squeeze through and fight off the infection. Do we need to know about what sort of antibodies they exhibit on their surfaces? If so, which antibodies are they?

5. Are mast cells embedded or are they free cells?

6. Do we need to know the different types of antibodies?

7. If antibodies have a y structure and have two antigen-binding sites, can both of these sites bind on two of the same antigens on the same pathogen?

8. How much do we need to know about inflammation, besides that mast cells releasing histamines for specific responses and there will be redness, swelling and pain at the site of infection?

9. Must we know about the lymphatic system including the vessels and direction flow ?

10. If B and T cells are both produced from stem cells in the bone marrow, and B cells mature in the bone marrow whereas T cells migrate to the thymus to mature, where are they kept in storage? Is it both in the spleen and lymph nodes or?

Many thanks.

1. Yes

2. N/A

3. Nope. Just note that it occurs when inflammation spills into the bloodstream, basically.

4. You need to know that they have IgE antibodies embedded in their surface. You should know the role that mast cells play in allergic reactions.

5. Free

6. Nope

7. Sure can. The variable regions of the antibody engages exactly the same target.

8. That's about it. You need to understand that other cells are also involved and why it happens as well, which you already seem to know.

9. Nope.

10. Essentially. The vast majority of B-cells and T-cells are stored in the spleen and in lymph nodes. They can, of course, get into tissues, including the blood, once activated (otherwise there's no point for them is there?)

[Biology24123]

Do we need to know where on the antibody epitopes bind to (light chain, heavy chain)

[cosine]

1. Yes

2. N/A

3. Nope. Just note that it occurs when inflammation spills into the bloodstream, basically.

4. You need to know that they have IgE antibodies embedded in their surface. You should know the role that mast cells play in allergic reactions.

5. Free

6. Nope

7. Sure can. The variable regions of the antibody engages exactly the same target.

8. That's about it. You need to understand that other cells are also involved and why it happens as well, which you already seem to know.

9. Nope.

10. Essentially. The vast majority of B-cells and T-cells are stored in the spleen and in lymph nodes. They can, of course, get into tissues, including the blood, once activated (otherwise there's no point for them is there?)

Very nice, thank you! (also on a personal note, no one ever replied for your bio lecture )

May I ask what these IgE antibodies do on the surface of mast cells? As I said, my textbook does not mention these so a bit unsure. Also what do mast cells do in response to allergens? I know they release histamines but whats this got to do with allergic responses?

Also, does DNA ligase get used on the leading strand of DNA replication? Or is it just the lagging strand? I have a theory but probably wrong. I guessed that because DNA polymerase synthesises from the 3'-5' direction without stopping, along the parent strand, there are no 'gaps' within which DNA ligase needs to act upon. Where as on the lagging strand, there are gaps known as okazaki fragments which are bonded together, that is, their phosphate backbones are bonded together by DNA ligase. Is this true or am I making this up?

Cheers.

[grannysmith]

Very nice, thank you! (also on a personal note, no one ever replied for your bio lecture )

May I ask what these IgE antibodies do on the surface of mast cells? As I said, my textbook does not mention these so a bit unsure. Also what do mast cells do in response to allergens? I know they release histamines but whats this got to do with allergic responses?

Also, does DNA ligase get used on the leading strand of DNA replication? Or is it just the lagging strand? I have a theory but probably wrong. I guessed that because DNA polymerase synthesises from the 3'-5' direction without stopping, along the parent strand, there are no 'gaps' within which DNA ligase needs to act upon. Where as on the lagging strand, there are gaps known as okazaki fragments which are bonded together, that is, their phosphate backbones are bonded together by DNA ligase. Is this true or am I making this up?

Cheers.

The IgE/mast cells act as mines. When enough allergenic particles bind to the antibodies such that cross linkages form, this causes the degranulation of the cells which releases histamines. Histamine is a chemical (signalling molecule) which causes blood vessels to dilate etc. which give rise to the typical symptoms of an allergic reaction.

That's correct.

Do we need to know where on the antibody epitopes bind to (light chain, heavy chain)

Yep, you need to be able to draw/label them too.

[cosine]

The IgE/mast cells act as mines. When enough allergenic particles bind to the antibodies such that cross linkages form, this causes the degranulation of the cells which releases histamines. Histamine is a chemical (signalling molecule) which causes blood vessels to dilate etc. which give rise to the typical symptoms of an allergic reaction.

That's correct.
Yep, you need to be able to draw/label them too.

Sorry grannysmith, I don't quite understand the mast cell part. IgE anitbodies are embedded within the surfaces of mast cells right? Is there a specific reason why you did IgE/mast cells? Just curious xD

Also, what do you mean, specifically by enough allergens binding to form cross linkages? And when you say the cells degranulate that release histamine, don't mast cells release histamine? o.O

[cosine]

Few more questions:

1. Do we need to know that monocytes will change into macrophages only when they squeeze through capillary walls into the infected area? If so, does this suggest that macrophages are only present in infected areas and hence cannot be present in the blood stream?

2. When a macrophage engulfs a foreign pathogen, it digests and degrades it. Antigenic fragments are then presented on the MHC II markers. What happens now? Where does this macrophage go, or what comes to it?

3. Do we need to know about TCRs? If so, are they only found within the membranes of Cytotoxic T cells or all types of T cells? (T Helper cells)?

[sunshine98]

do we need to know about antigenic variation ?

anyone?

[Biology24123]

Few more questions:

1. Do we need to know that monocytes will change into macrophages only when they squeeze through capillary walls into the infected area? If so, does this suggest that macrophages are only present in infected areas and hence cannot be present in the blood stream?

2. When a macrophage engulfs a foreign pathogen, it digests and degrades it. Antigenic fragments are then presented on the MHC II markers. What happens now? Where does this macrophage go, or what comes to it?

3. Do we need to know about TCRs? If so, are they only found within the membranes of Cytotoxic T cells or all types of T cells? (T Helper cells)?

2. After antigen presentation , a specific T helper cell recognizes
3. You need to know it, They are found on helper, cytotoxic and memory T cells
 

[grannysmith]

anyone?

You need to know what it is and its implications, but not any specifics on how its done (just a general idea i.e. genes are shuffled).

Sorry grannysmith, I don't quite understand the mast cell part. IgE anitbodies are embedded within the surfaces of mast cells right? Is there a specific reason why you did IgE/mast cells? Just curious xD

Also, what do you mean, specifically by enough allergens binding to form cross linkages? And when you say the cells degranulate that release histamine, don't mast cells release histamine? o.O

You need both the IgE and mast cell to release the histamine. In this way, the pair act as a unit.

Okay, so histamine will only be released if enough allergens bind so as to form cross linkages. You can think of it as a threshold level - you need a certain number of allergens to bind to the IgE in order to activate the mast cell. Yeah I was inferring cells=mast cells, and that they degranulate=release histamine (this is because histamines are stored in granules within the cell).