VCE Biology Question Thread

[PhoenixxFire]

So given they have both I would guess they are structurally different and I know that Tc cells bind to MHC 1 and Th bind to MHC 2. It confuses me though how a Tc cell can tell that an MHC marker is a non self or mutated MHC 1 marker rather than thinking it is a MHC 2 marker or any other membrane bound protein. Because Tc cells have a CD8 receptor that binds to the MHC then another receptor that binds to the presented peptide fragment right? But how does the CD8 know that it can't bind because the MHC is non self versus not being able to bind because it is a different molecule?

[vox nihili]

So given they have both I would guess they are structurally different and I know that Tc cells bind to MHC 1 and Th bind to MHC 2. It confuses me though how a Tc cell can tell that an MHC marker is a non self or mutated MHC 1 marker rather than thinking it is a MHC 2 marker or any other membrane bound protein. Because Tc cells have a CD8 receptor that binds to the MHC then another receptor that binds to the presented peptide fragment right? But how does the CD8 know that it can't bind because the MHC is non self versus not being able to bind because it is a different molecule?

You're right, they're structurally different. Won't go into the details other than to say they are.

The immune system can't actively recognise self (for the most part). Knowing that something is non-self isn't an active process. Immune cells only have receptors that respond to non-self molecules. Something that is self is self because the immune system can't respond to it.

T-cells can recognise that an MHC class I or II is non-self because those molecules hold chunks of protein (called epitopes) inside them. These chunks of protein are the antigens that are expressed and those that allow T-cells to recognise non-self.

[Robert16]

Hi guys, will rank 5/35 in a decent cohort give me room for a 40+ study score?

[LifeisaConstantStruggle]

Hi guys, will rank 5/35 in a decent cohort give me room for a 40+ study score?

depends on what school you're in but  it's hard to predict just from your rank, just work hard and ace the exam I'm sure you can do it

[zxcvbnm18]

Howcome the oldest rocks found in canada not widespread?

[PhoenixxFire]

Howcome the oldest rocks found in canada not widespread?

They haven't found them elsewhere but that doesn't mean they aren't there. The Earth is a big place. Rock can also undergo metamorphic change that  will stop them from being accurately dated. They just happened to be found in Canada.

[Atlantis]

I have a question on DNA hybridisation

Okay so when you have two different organism's DNA and you heat them up to become single-stranded and then mix them up, what stops them from just going back to their exact complementary strand (the same organisms DNA?) - i understand it's the 'mixing' of them but i don't think i get what that actually means.

[vox nihili]

I have a question on DNA hybridisation

Okay so when you have two different organism's DNA and you heat them up to become single-stranded and then mix them up, what stops them from just going back to their exact complementary strand (the same organisms DNA?) - i understand it's the 'mixing' of them but i don't think i get what that actually means.

Excellent question. Shows you're really thinking about what's going on.

You're quite right. Many of the strands will mix with their normal complementary strands; however, many also will not. It's these that you rely on to generate your result

[Mr West]

Hey guys,

ive got a non-3/4 bio question. (its unit 2 bio)

What is the point of reversibly dissociating a double helical structure into two single DNA chains?
(So heating it to dissociate and then cooling so the chains re-associate)

Thanks

[PhoenixxFire]

By itself? not much. In 3/4 we learn that its used for Dna hybridisation (used to test relatedness between species) and for PCR (Used to amplify sections of DNA.

[LifeisaConstantStruggle]

Hey guys,

ive got a non-3/4 bio question. (its unit 2 bio)

What is the point of reversibly dissociating a double helical structure into two single DNA chains?
(So heating it to dissociate and then cooling so the chains re-associate)

Thanks

this involves some knowledge of unit 4 bio (correct me if I'm wrong), but heating a DNA double helix to split them into respective single strands can have some uses, mainly 2 (you'll be taught this in unit 4).

1) Polymerase chain reaction (PCR), which is a technique used to replicate DNA (and lots of it) by heating DNA double strands to form single strands then attaching nucleotides on the 2 single strands to form a copy of double stranded DNA (this process is then repeated to form more and more copies of DNA).
2) DNA-DNA hybridisation, which is used to determine the relatedness between two species. For example, if you want to test the relatedness between a banana and a human being you can extract both their DNA, heat them up to split their DNA into single strands and mix their DNA together. By cooling it down some DNA strands would combine with DNA strands of the other species, forming hybrid DNA strands. (also because nucleotides only form bonds with complementary nucleotides eg. A to T, C to G, there will be some unconnected parts of the hybrid DNA strands as some nucleotides from the DNA single strand of 1 species are not complementary to the DNA single strand of the other species). This, would make the hybrid DNA strand easier to be split into single strands again just by heating it up (they generally split at a lower temperature), so the lower the temperature in which the DNA strands are split, the less related the two species. (I hope I explained this well)

[Mr West]

(I hope I explained this well)

Thanks heaps! That is perfect

[KANYEWEST]

hey yall,

i need help constructing a really good Hypothesis for temperature effect on enzymes!

If anyone can help me!
Thanks xx

[LifeisaConstantStruggle]

hey yall,

i need help constructing a really good Hypothesis for temperature effect on enzymes!

If anyone can help me!
Thanks xx

Hello, (as this is the hypothesis there's no need to mention enzyme denaturation or anything like that)
The higher the temperature deviation between the experimental group and the optimal temperature for the function of [insert enzyme here], the lower the rate of reaction of [substrate] completely into [product] in the presence of [enzyme]. I hope I'm not lacking information but here you go.

[KANYEWEST]

Hello, (as this is the hypothesis there's no need to mention enzyme denaturation or anything like that)
The higher the temperature deviation between the experimental group and the optimal temperature for the function of [insert enzyme here], the lower the rate of reaction of [substrate] completely into [product] in the presence of [enzyme]. I hope I'm not lacking information but here you go.

OMG THANK YOUUUUUU!