hi
VCE Biology Questions Thread
- Edited
Hi chimichurri!
Let me try and explain how operons/genes work.
Firstly, remember that a gene is a section of DNA that codes for a specific protein. Of course, genes are found in both eukaryotes and prokaryotes. A gene will code for multiple amino acids, forming a polypeptide chain that can be folded to form a functional protein. An operon is generally only found in prokaryotes, and its a cluster of linked genes that all share a common promoter and operator, and are transcribed at the same time. Generally, all of these genes are related by function (i.e. biochemical process that they are a part of). Now, the genes in the operon are structural genes (genes that don't code for regulatory proteins, but instead proteins needed for structure or cellular functioning). The trp operon (that you need to know about from the study design) consists of multiple structural genes and has a structure like the following:
3' end - Promoter - Operator - Leader (TrpL) - Attenuator - TrpE - TrpD - TrpC - TrpB - TrpA - Trailer - 5' end
TrpE to TrpA are your important structural genes. As we know, genes code for many amino acids, so an operon is not going to just code for amino acid. It is easy to think that the trp operon codes only for one amino acid, that being tryptophan (since the process can be quite confusing to understand). However, the trp operon actually codes for multiple polypeptides, each structural gene being transcribed and translated to form different proteins (specifically enzymes) that are required to produce tryptophan. Here are some details on the enzymes formed (don't need to know the specifics, but it can be helpful in understanding how it works).
- TrpE and TrpD -> Form enzyme Anthranilate synthase, which converts chorismate (found in the cell) into anthranilate.
- TrpC -> Forms enzyme Indole-3-glycerol-photosphate synthase, which converts anthranilate into indole-3-glycerol-photosphate.
- TrpB and TrpA -> Forms enzyme Tryptophan synthase, which converts indole-3-glycerol-photosphate into tryptophan.
(Requires lots of energy, meaning the process needs to be tightly regulated via attenuation and repression mechanisms).
To put it simply, the enzymes are produced to convert certain chemical products into tryptophan, with each enzyme consisting of many amino acids that form polypeptides and therefore are folded into functional proteins (i.e. enzymes). Hopefully that makes sense.
With directions, it can be quite confusing. RNA polymerase (not pre-mRNA) reads the strand in a 3' to 5' direction, forming an mRNA strand (mRNA for prokaryotes, but pre-mRNA for eukaryotes) that is 5' to 3' (due to complementary nature of DNA transcription). DNA replication is the same, as DNA polymerase reads the strand from 3' to 5' and writes a new DNA strand from 5' to 3'. I remember it like this: "When we study, we read up on a topic (3' to 5'), and then you write it down (5' to 3')". That said, google makes it kind of confusing by saying that DNA is read 5' to 3', but I'm assuming that it is referring to the fact that whilst the template strand being copied in a complementary manner is the 3' to 5' direction, the actual coding strand that is being replicated is 5' to 3' (which is why the created DNA or RNA strand is always written in a 5' to 3' direction). I might be wrong about that though. Not sure if that makes sense, since I'm still trying to wrap my head around how it works haha.
how does natural selection contribute to allopatric speciation
chemistry1111
Allopatric speciation begins with a species population being separated due to a geographical barrier (e.g. ocean, mountain ranges, vast desert, etc.). These populations will therefore be exposed to different environmental selection pressures, resulting in the accumulation of genetic differences. During this process, natural selection will confer an selective advantage to members of these populations that carry advantageous alleles, of which increase their fitness and ability to survive when exposed to these different selection pressures. It is important to note that of course, the selection pressures will vary and therefore the members of each population selected for and against by natural selection will differ. Over time, this process of natural selection will result in the population members being unable to interbreed if they come in contact with each other (i.e. the geographic barrier is removed), as they will no longer be able to produce viable and fertile offspring.
Hello there,
Can someone please explain to me why fermentation must not allow the presence the oxygen to happen successfully? (Like I get it's because that's anaerobic respiration but I don't know what would happen if we have oxygen present in it?).
Cheers 
I'm not sure on the bio-mechanics of it all - perhaps its got to do with the build up of pyruvate molecules - but the gist of it is:
Aerobic respiration is more efficient. So it will be conducted when sufficient oxygen is available.
Fermentation will occur when there is not enough oxygen - as it provides an alternate means of re-cycling the NADH molecules.
Hello there,
Can someone please explain to me the process of monoclonal antibodies and how effective this method is when we use it as a treatment for a disease?
Kind regards
- Edited
hey, what is the difference between coding strand
chemistry1111
Hi
The template strand only serves as the template for transcription (so this template strand is often from DNA, and is used to transcribe into mRNA). Whereas, the coding strand contains the exact same sequence of nucleotides in the mRNA except for thymine.
Hope this helps
5 days later
_sophiestudies_
Thank you so so so much! I understand now
hi all! sorry if someone's already asked this question:
does anyone know if there are solutions available for the 2022 sample bio exam on the vcaa page? and if so where they are located?
my teacher literally made the class complete it under timed conditions and everything but we can't even correct our work...
thanks in advance!
-bw
bw304 I don't think there are any solutions (VCAA doesn't seem to ever give sample exam solutions for any subject, which is really annoying). You might need to ask your teacher for answers, or see if they can mark it for you.
Can someone please explain part b of this question from the 2019 VCAA exam? Like i get that the mitochondrial DNA of the girl’s finger bone will be very similar to the mtDNA of her female ancestors, but I dont get why. MtDNA has a high mutation rate but it remains relatively unchanged from one generation to another- can someone pls explain what the concept is behind mtDNA and how that links to this question? Cos the way the edrolo textbook has explained it is kinda contradictory..
Also can someone explain Q4 from the 2020 VCAA exam’s multiple choice section? How do we know that substrate B is gonna be a competitive reversible inhibitor? I actually thought substrate B wouldn’t even bind to the active site cos its not forming a product 
- I’ve been a bit confused with these two questions since yesterday so if someone could help clarify this in detail that’d be great. Thanks so much!
With the 2020VCAA question - I think the clue is that is says 'an enzyme-substrate complex was formed in each of the three test tubes'. This indicates that both substrates have bound to the enzyme. Then - I think its a matter of trial and error.
Intuitively, i would expect it to either decrease - or stay the same. Then going through each option:
Option A) can't be true because - it doesn't make sense. The only way substrate A & B could both bind at the same time would be if B was an allosteric inhibitor - in which case you would expect to see no product. But the option says it would be the same as testube 1. It could be a co-enzyme - but then you would expect test-tube 1 to have no product produced.
Option B) can't be true because substrate b can form an 'enzyme-substrate complex'. Which means, some of the time it will be bonded to the active site. Hence the rate of reaction would decrease - as it doesn't actually make a product when bound.
Option C) sounds ok.
Option D) sounds ok.
Now I'm not 100% sure on the logic to differentiate between C & D. Looking through my old prac exams from last year - I chose C. I think this is why:
Whenever an answer says something definite - like ' zero' product produced - I tend to doubt it. Even if it was an irreversible inhibitor - some product (theoretically) would still get produced.
Apologies for the long-winded response. Maybe someone else can help more.
Also - Mitochondrial DNA is passed down from mother to child. (Unlike chromosomal DNA which is 50/50 split from mother/father)
Without reading the article - I presume the time-span was too small to pickup any differences in mitochondrial DNA. It could also be that - due to recent interbreeding between the two species - the girl could have mtDNA of her mother's species. Which might be very different to her father's.
Hello Smartiestarz!
Can someone please explain part b of this question from the 2019 VCAA exam? Like i get that the mitochondrial DNA of the girl’s finger bone will be very similar to the mtDNA of her female ancestors, but I dont get why. MtDNA has a high mutation rate but it remains relatively unchanged from one generation to another- can someone pls explain what the concept is behind mtDNA and how that links to this question? Cos the way the edrolo textbook has explained it is kinda contradictory..
mtDNA does not change from generation to generation as much as nuclear DNA because it does not undergo recombination. It is solely inherited maternally (well... in most cases anyways).
Think about it like this; suppose you have a deck of cards. Which would result in a more drastic change?
- Changing, adding, or taking away a card every now and then.
- Shuffling the cards, and replacing half of them from another shuffled deck.
Scenario 1 would be comparable to spontaneous mutations in mtDNA, and Scenario 2 would be comparable to genetic recombination. Sure, mtDNA may accumulate mutations faster than nuclear DNA, but it is still relatively insignificant when compared to nuclear DNA recombination.
Also can someone explain Q4 from the 2020 VCAA exam’s multiple choice section? How do we know that substrate B is gonna be a competitive reversible inhibitor? I actually thought substrate B wouldn’t even bind to the active site cos its not forming a product
This was a bad question. Usually we would not call an inhibitor a "substrate" at all, we would call them inhibitors.
Basically you had to choose the most plausible option, option C. The other options didn't really have any coherence.
- Option A - Why does both substrate being able to bind to the enzyme simultaneously result in same product output?
- Option B - How would product output change if the same amount of substrate is added?
- Option D - If substrate B was an irreversible inhibitor, then why are the enzyme and substrate B shown as separate for the results of test tube 2?
Again, the question is pretty bad. Is the experiment under timed conditions? If not, reversible competitive inhibitor shouldn't make a difference in the end... etc.
Hey! So enzymes increase the reaction rate by lowering the activation energy required for a reaction, I was wondering how enzymes do that? I've read that an example of how they lower the activation energy is by bringing reactants together which reduces the amount of energy they use moving around until they collide, is this the only way that they reduce the activation energy?