VCE Biology Question Thread

[gameboy99]

A few questions...
Does cytokines cause blood vessel dilation and increased permeability or is that the sole responsibility of histamine secreted by mast cells, basophils and platelets?
I read that complement proteins have to functions in addition to lysis which is opsonization and inflammatory response. Which is used in this case??

[vox nihili]

A few questions...
Does cytokines cause blood vessel dilation and increased permeability or is that the sole responsibility of histamine secreted by mast cells, basophils and platelets?
I read that complement proteins have to functions in addition to lysis which is opsonization and inflammatory response. Which is used in this case??

There are some other mediators involved, but at this point assuming just histamine is responsible for that is acceptable.

All three. Opsonisation just refers to helping phagocytosis, and complement can also play a role in spurring on inflammation. Lysis you've already described.

[gameboy99]

So does that mean that APC cells secreting cytokines will first recognize damaged cells, initiating inflammation. Then the mast cells, basophil and platelets will secrete histamine dilating the blood vessels and making it more permeable.
OR do both work simultaneously??

[vox nihili]

So does that mean that APC cells secreting cytokines will first recognize damaged cells, initiating inflammation. Then the mast cells, basophil and platelets will secrete histamine dilating the blood vessels and making it more permeable.
OR do both work simultaneously??

It's not just damaged cells they sense, it's also pathogens.
But yeah that's the essence of it—shit loads of cytokines, then boom mast cells go off.


Mast cells, however, can also be activated directly by an antigen too (via IgE)

[gameboy99]

Thanks Mr T-Rav for answering the barrage of questions I had! Helped heaps.

[chickennugget]

During DNA replication, what exactly replicates? Before a cell replicates, it is in G1 phase, and the DNA is in chromatin form. Is it this chromatin that replicates?

(Mitosis) During prophase, do we have chromosomes that have two sister chromatids that are genetically identical joined at a centromere? Or are these chromatids different (one from mother/father)? Assuming they are genetically identical, when the chromosome splits into individual chromatids, we end up with genetically identical cells?

[The Usual Student]

During DNA replication, what exactly replicates? Before a cell replicates, it is in G1 phase, and the DNA is in chromatin form. Is it this chromatin that replicates?

(Mitosis) During prophase, do we have chromosomes that have two sister chromatids that are genetically identical joined at a centromere? Or are these chromatids different (one from mother/father)? Assuming they are genetically identical, when the chromosome splits into individual chromatids, we end up with genetically identical cells?

Chromatin and chromosomes are pretty much the same thing except they differ by structure. Chromosomes are coiled tightly and hence are densely packed which is much more efficient for cell replication.
First question: Yeah it duplicates whilst the DNA is in a chromatin form
Second question 1) No sister chromatids are identical and will always be identical by definition. So it can't be from your mother and father. A homologous pair of chromosomes is when you get one from mom and one from dad
2) yeah you are correct, mitosis results in two identical daughter cells

edit: To help with your understanding, sister chromatids are the result of DNA replication. Hence, they are IDENTICAL. Whilst something like homologous pairs  (what you are getting confused with) are simply a pair of chromosomes that are the same structure and have the same gene loci but don't necessarily have the same alleles in those genes. IN other words, a  paid of chromosomes in which one is given  by your mom and one is given by your dad.

[vox nihili]

During DNA replication, what exactly replicates? Before a cell replicates, it is in G1 phase, and the DNA is in chromatin form. Is it this chromatin that replicates?

(Mitosis) During prophase, do we have chromosomes that have two sister chromatids that are genetically identical joined at a centromere? Or are these chromatids different (one from mother/father)? Assuming they are genetically identical, when the chromosome splits into individual chromatids, we end up with genetically identical cells?

Chromatin and chromosomes are pretty much the same thing except they differ by structure. Chromosomes are coiled tightly and hence are densely packed which is much more efficient for cell replication.
First question: Yeah it duplicates whilst the DNA is in a chromatin form
Second question 1) No sister chromatids are identical and will always be identical by definition. So it can't be from your mother and father. A homologous pair of chromosomes is when you get one from mom and one from dad
2) yeah you are correct, mitosis results in two identical daughter cells

edit: To help with your understanding, sister chromatids are the result of DNA replication. Hence, they are IDENTICAL. Whilst something like homologous pairs  (what you are getting confused with) are simply a pair of chromosomes that are the same structure and have the same gene loci but don't necessarily have the same alleles in those genes. IN other words, a  paid of chromosomes in which one is given  by your mom and one is given by your dad.

Great explanation, but I'm just going to refine the definition of chromosomes and chromatin. A chromosome refers to a single molecule of DNA (i.e. one double helix). In humans, we have 46, arranged in 22 or 23 pairs (because XX in women, but XY in men).
Chromatin, on the other hand, is what chromosomes are made out of. DNA doesn't just float around freely in the cell. It wraps around proteins called histones, which help it to coil and form nice bundles. So chromatin is, therefore, DNA and the histones around which it is wrapped.

As far as replication is concerned (the S phase of the cell cycle), DNA and the histones are replicated—so chromosomes replicate, as the Usual Student described, but so does chromatin (of course it does, because it's what makes up the chromosomes).


tl;dr: chromosomes are the chunks of DNA and protein, chromatin is what those chunks are made of.

[instax101]

I was hoping if someone could explain to me why the answer in the attached exam question (Question 24) is B.

Thanks

[chickennugget]

Attenuated viruses are a weakened version of a virus, and it is made into a vaccine that can be injected into the bloodstream. (C) is incorrect as the attenuated virus, as it is quite weak, will not readily infect cells, therefore cytotoxic T cells are not needed to kill infected cells. However, the attenuated virus is still recognised as an antigen, and therefore memory B cells are still produced. They remain in the lymphatic system until the real virus infects the body. The presence of these antibodies is beneficial as it allows antibodies to be produced faster and in larger numbers. Therefore (B) is correct.

[gameboy99]

1. Does APC release interleukin 1 or does T-helper cell release interleukin 1 after APC and T helper cell bind??
2. I understand that Interleukin 2 is released by activated T-helper cell which causes the proliferation of certain cytotoxic T cells and B cells, but does it also cause T-helper cells itself to multiply??

[vox nihili]

1. Does APC release interleukin 1 or does T-helper cell release interleukin 1 after APC and T helper cell bind??
2. I understand that Interleukin 2 is released by activated T-helper cell which causes the proliferation of certain cytotoxic T cells and B cells, but does it also cause T-helper cells itself to multiply??

1/2. Not in the slightest bit within the course, don't worry about it.

[gameboy99]

If that's too much detail what basic idea do I have to know about that part???

[vox nihili]

If that's too much detail what basic idea do I have to know about that part???

That T-cells bind APCs and get activated.
That cytokines coordinate the immune response (controlling growth of any number of cells).


To address your actual question, the cytokines involved are actually a bit tricky to understand. There are actually different subsets of B-cells and T-cells, and these different subsets are "controlled" by different cytokines. Basically, better to avoid that and just stick to the VCE-level stuff!

[Gogo14]

How do the B cells in the lymph nodes get activated? Do the antigens wander through the body until they encounter a B cell with the matching antibodies in the nodes?or does an APC travel from the site of infection to the nearest node to activat the B cells?