VCE Biology Questions Thread

_sophiestudies_

johntenpiece I'm not entirely sure how important ELISA will be for the exam, but it is a helpful example of an immunological method of identifying pathogens.

Steps of the sandwich method of ELISA = Enzyme-linked immunosorbent assay:

Antibodies specific to a certain pathogen are attached to a plate.
The serum (fluid and solute components of blood) sample being tested is applied to the plate. This means the antibodies will attach to any pathogen antigens that correspond in a complementary manner to its antigen-binding site.
Second detection antibody, linked to a colour changing enzyme, is added to the plate. It will bind to any antibody-antigen complexes.
Substrate is then added for the enzyme, reacting to this enzyme on the second antibody and changing colour to reveal whether any pathogenic antigens are present. Note that it can only bind to the substrate if the enzyme has bound to the antibody-antigen complexes, as this process likely (I think, but I'm not 100% sure) alters the active site of the enzyme to facilitate it binding to the substrate.

Note: There are also three other types of ELISA tests -> Direct, indirect, and competitive. I don't know anything about these, but if someone does, I'd love to know about it!

clazah

whats the difference between an attached and free antibody?

God

clazah ummm…. Could be wrong, but Is the first one bound to some membrane/cell type thing. Where the other one is free to float around?

Like the literal meaning of ‘attached’, and free meaning not-attached?

Could be wrong though. (New study design an all) Hope this helps : )

bioho4

clazah attached antibody = antibody on a B cell; used during clonal selection in humoral response.
Free antibody = singular antibody floating in either the blood or lymph, which can bind to antigens on pathogens and create an antibody-antigen complex. This enhances phagocytosis of the pathogen.

_sophiestudies_

clazah attached might be referring to membrane bound antibody receptors (like God said). That would include B cell receptors (not T cell receptor though because they're not a type of antibody). Free antibodies would just be the antibodies produced by plasma B cells to target specific antigens, causing opsonisation, agglutination, neutralisation, etc.

Edit: Haha bioho4! Two minds think alike!

clazah

what is the ATP yield of ETC?

_sophiestudies_

clazah 26 or 28 ATP (it's on the biology FAQ document on the VCAA website, as most textbooks have the numbers wrong).

atarwonders

do we need to know about DNA hybridisation?

_sophiestudies_

atarwonders nope. That was from the last study design, so you can ignore those questions!

clazah

can somebody please explain this multiple choice question: The insulin produced by recombinant DNA technology is.. the answer was; produced from human insulin mRNA.

tubes

clazah I was confused about this trial question too, and instead I chose C, and I confirmed with my teacher that B wasn't the best answer out of them

clazah

whats the difference between universal and degenerate?

_sophiestudies_

clazah
Universal = Same codons code for the same amino acids in different species. This is all about the "universal" nature of the codon to amino acid system.

Degenerate = Multiple codons code for the same amino acid -> Results in a level of redundancy, whereby some mutations won't actually alter the amino acid (silent mutation)

Christ

I was doing a multiple choice question from the practice exams Nelson net provided, and one of the questions implied that you knew the difference between degeneracy and redundancy.
Is there a difference at all?

Thanks

tubes

Christ I know which question your talking about, and I was suggested to ignore this question, but just searching it on google wasn't much help and seems like more of a niche thing rather than something were likely to be assessed on

chemistry1111

if we have too much tryptophan will it become toxic ?

tubes

chemistry1111 No, trp is an amino acid and its not because of its toxicity the trp operon exists, but rather its synthesis is very energy costly, so continual expression of the trp genes could deplete the cell of ATP. And that's why these structural genes are regulated in an operon to conserve this ATP when trp is already present

Christ

tubes
B is the best answer and here is why.
When DNA is needed to be inserted into the plasmid of a bacteria, it must not contain the introns. This is due to the prokaryotic DNA not containing introns and hence does not undergo RNA processing.
The reason the human insulin is produce by the human insulin mRNA is because the human mRNA does not contain introns. The enzyme invertase is then used to convert the intron free mRNA in to DNA strand, that does not contain introns. Hence DNA is able to be inserted into the bacterial plasmid to produce the correct gene produce, insulin.

I hope this makes sense

tubes

Christ Hi! Yes I understand the fact about the mRNA not containing introns, however if you read the entire sentence together "The insulin produced by recombinant DNA technology is produced from human insulin mRNA," though accurate is not as good as "The insulin produced by recombinant DNA technology is produced by a cloned human insulin gene."
And the reason why C is a better answer is because the mRNA undergoes further processing as you mentioned to convert into into DNA, and hence its not actually the mRNA producing the insulin but rather the copy DNA produced by Reverse transcriptase (invertase in an enzyme that catalyses sugar btw). Thus C would be a better answer

md2112

Hey i need help with the answer for 9a for the sample exam, my teacher said it was homo erectus but im still confused

bioho4

md2112 what was the explanation given for saying it's homo erectus? Denisovans makes the most sense imo because its the only ancestral species that shares DNA with Indigenous Australians, as said in the article in the question

tubes

md2112 The explanation is that H. floresiensis had a much small stature and couldn't be the ancestor of the otherwise taller Indigenous Australians. H. densiova can't be because they share only a small percentage of DNA, and if it was the ancestor it would show much greater genetic similarity, thus the small percentage of DNA similarity would be because of interbreeding rather than descent. For example, Neanderthals and modern H.sapiens share max 5-7 percent (smth like that) DNA in common, but we say they shared a common ancestor and interbred rather than Neanderthals being the ancestor of H.sapeins, the same logic applies here.

Pasta

md2112 It is Denisovans. There is 4-6% similarity in the nuclear DNA shared amongst Indigenous Australians, Papua New Guineans and Indonesians and this covers the likely route to Australia (as seen in the article). Homo erectus and Home floresiensis were in the areas near Sahul at the time of the migration to Australia but none of their nuclear DNA is shared with indigenous Australians.
(It’s not H. erectus because the article states clearly that no other species apart from Denisovans shared nuclear DNA with Indigenius Australians).

md2112

Also for 10d im unsure about the marking

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