VCE Biology Question Thread

[homosapien]

Are genes only found in DNA? Not mRNA?

[The Usual Student]

Are genes only found in DNA? Not mRNA?

yep genes are only in DNA
RNA does not hold genes but rather a better term is the codons that are associated with the amino acids that will construct the polypeptide that the gene codes for

[Angelx001]

cytotoxic T cells destroy cells that present fragments on it's MHC 1 surface proteins- does this mean they first have to be activated by helper T cells?

[Angelx001]

cytotoxic T cells destroy cells that present fragments on it's MHC 1 surface proteins- does this mean they first have to be activated by helper T cells?

[Calebark]

can someone tell me what we really need to know about the blood antigen system :p
My teacher said it really wasn't important

I don't think we need to know about it directly. We already know how antibodies work, and that's all we need to know. The only question I've seen about it was Q24, from the Multiple Choice of 2009, Exam 1. Everything you need to know is in the stem, or drawn upon from the basics of the immunity course.

cytotoxic T cells destroy cells that present fragments on it's MHC 1 surface proteins- does this mean they first have to be activated by helper T cells?

Yes, I believe so.

[AhNeon]

So just wanted to cement my knowledge
When a pathogen enters the body, macrophages or other phagocytes can identify and engulf them. After this, the macrophage present an antigen of the pathogen on its MHC 2 marker and travels to the lymph nodes where it presents this to different specific helper T cells. Once the correct Th cell is activated, it releases cytokines which stimulate B cells and Tc cells. B cells undergo that whole humoral response thing and Tc cells go to tissues and read MHC 1 via its T cell receptor attempting to find affected cells to which it uses perforin and granzyme to destroy the cell/induce apoptosis.
Is this all correct?

Also is there any difference between fermentation and anearobic respiration?

[Yacoubb]

So just wanted to cement my knowledge
When a pathogen enters the body, macrophages or other phagocytes can identify and engulf them. After this, the macrophage present an antigen of the pathogen on its MHC 2 marker and travels to the lymph nodes where it presents this to different specific helper T cells. Once the correct Th cell is activated, it releases cytokines which stimulate B cells and Tc cells. B cells undergo that whole humoral response thing and Tc cells go to tissues and read MHC 1 via its T cell receptor attempting to find affected cells to which it uses perforin and granzyme to destroy the cell/induce apoptosis.
Is this all correct?

Also is there any difference between fermentation and anearobic respiration?

Your outline of immunity is correct. Theoretically, fermentation and anaerobic respiration are the same. However, I have personally found that using the word fermentation is more suitable for the anaerobic respiration occurring in plants/yeast, whilst just calling it anaerobic respiration for animals (some call it lactic acid fermentation).

[Yacoubb]

can someone tell me what we really need to know about the blood antigen system :p
My teacher said it really wasn't important

As others have mentioned, you don't need to know anything too extensive about it. Any questions related to antigen-antibody complex formations regarding ABO antigens will be testing your understanding of how interactions between antigens and antibodies -> agglutination. Any genetics questions relating to these will be accompanied by alleles (e.g. I^A, I^B, i) and so you don't have to memorise them.

[hodang]

So do cytotoxic T cells recognise antigenic fragments that are present on their MHC Class 1 markers?

Ps- Thankyou Vox nihil

[Yacoubb]

So do cytotoxic T cells recognise antigenic fragments that are present on their MHC Class 1 markers?

Ps- Thankyou Vox nihil

Yep! So basically the entire purpose of having infected cells display antigenic fragments (also known as epitopes) on MHC class I markers is so that cytotoxic T cells are able to identify cells infected with the specific pathogen. The additional reason for this is actually because unlike B cells which can recognise antigens in their native conformation (e.g. if they're attached to a pathogen or found in the serum they can readily bind the surface immunoglobulin of a naive B cell), T cells cannot actually recognise antigens in this way. The antigens must be processed (i.e. broken down into fragments - epitopes) and then displayed on MHC class I receptors (or II in the case of antigen-presenting cells) in order for them to be recognised by Tc and Th cells, respectively.

[hodang]

Thank you soo much Yacoub!

[Yacoubb]

Thank you soo much Yacoub!

My pleasure!

[QueenSmarty]

Hey everyone, I'm having trouble with linked genes and the ratios, and the way we represent them. What exactly do we have to know about them?

[Yacoubb]

Hey everyone, I'm having trouble with linked genes and the ratios, and the way we represent them. What exactly do we have to know about them?

Linked genes are genes located on the same chromosome. The idea about them is that if you have linked genes, the chances that they are independently assorting has decreased because of the reduction in the chance of crossing-over separating them. In fact, the closer they are, the more likely they are to move around completely dependent on one another. As a result, your gamete combinations for such genes will be limited. E.g. if you're AaBb, one of your homologous chromosomes may have AB and the other ab, and so we represent this as (alleles on one chromosome of homologus pair) / (alleles on other chromosome of homologous pair) - hence, AB/ab. Instead of having 4 possible gamete genotypes, you'll have only 2 (see VCAA 2015 exam for the q on writing out the gametes in the table. Your ratios will vary depending on the actual genotypes you're dealing with.

[QueenSmarty]

Linked genes are genes located on the same chromosome. The idea about them is that if you have linked genes, the chances that they are independently assorting has decreased because of the reduction in the chance of crossing-over separating them. In fact, the closer they are, the more likely they are to move around completely dependent on one another. As a result, your gamete combinations for such genes will be limited. E.g. if you're AaBb, one of your homologous chromosomes may have AB and the other ab, and so we represent this as (alleles on one chromosome of homologus pair) / (alleles on other chromosome of homologous pair) - hence, AB/ab. Instead of having 4 possible gamete genotypes, you'll have only 2 (see VCAA 2015 exam for the q on writing out the gametes in the table. Your ratios will vary depending on the actual genotypes you're dealing with.

Thank you!!