VCE Biology Question Thread

[f0od]

This is a bit more complex than what VCE covers but there are certain types of ATPase's that actually catalyse the synthesis of ATP from ADP (but yes other ATPase's, eg P-type, break down ATP to ADP and release energy).

In the thylakoid membrane, you usually have a F-ATPase (which is quite often referred to as ATP synthase). During photosynthesis, protons are actively pumped from the stroma to the lumen which creates a proton gradient. H+ can then passively travel back down the gradient across the membrane through ATPase which drives the synthesis of ATP from ADP + Pi. H+ formed from the splitting of water also pass through ATPase to create ATP. 

So they are actually synthesising ATP which can then be used in the Calvin cycle and are more commonly referred to as an ATP synthase.

Thanks for the detailed reply! 
Unfortunately, the question from my test 'The enzyme found in abundance on the thylakoid membrane would be:' was a multiple choice question with both ATPase and ATP synthase as possible answers, and ATPase was the right answer, so I'm not sure how to explain that 

[vox nihili]

I could be very incorrect with my response. It has been a while since I did photosynthesis so maybe someone else on here with more knowledge on the topic could explain better and correct me

Sorry for any confusion if I end up being incorrect!

Your answer was right. ATP synthase should be accepted as an answer here, too.

[Evolio]

Hello guys!
Just had a question about gene regulation.
You know how the enzyme binds to the repressor protein which prevents it from binding to the operator region, do other things bind to the repressor protein as well?
Like, what is an inducer?
Also, what does it mean by the repressor protein being 'inactivated'? Does it mean, it changes shape?

[Erutepa]

Hello guys!
Just had a question about gene regulation.
You know how the enzyme binds to the repressor protein which prevents it from binding to the operator region, do other things bind to the repressor protein as well?
Like, what is an inducer?
Also, what does it mean by the repressor protein being 'inactivated'? Does it mean, it changes shape?

For gene regulation in 3/4 bio, you study the LAC operon which is found within certain bacteria that produce lactase to breakdown lactose.
An operon is a section of DNA composed of a section of related genes with an upstream operator all under the control of a promoter as shown simply in the below diagram

You will notice that upstream of this operon is a corresponding regulatory gene. This will be expressed to produce a repressor protein which is complementary to the operator.
An inducer is a molecule that will bind to this regulatory protein to inactivate the repressor protein via a confirmation/shape change which prevents binding to the operator. For 3/4 biology at least, the inducer will always be the allolactose (or sometimes just lactose) because we study the LAC operon.

Thus, if this allolactose (inducer) is absent, the repressor protein will bind to its complimentary operator region and will block the action of RNA polymerase, thus preventing the expression of the genes within this operon. However, is allolactose is present, the allolactose (inducer) will bind to the repressor protein and cause a conformation change which prevents complementary binding to the operator region, thus enabling the binding of RNA polymerase thus the expression (induction) of the genes contained within that operon.

Hope this helps!

[maheenkhan]

What is the reason for an increase in the rate of cellular respiration due to increasing oxygen concentration? Is it because since oxygen is the final electron acceptor, more water can be formed? But water is a waste product. Also, why does the rate of cellular respiration increase with oxygen concentration up to a certain point?

Is it correct that most eukaryotes and some microbes (yeast) undergo aerobic respiration, whereas most microbes perform anaerobic respiration, as well as skeletal muscle cells?

Thanks!

[PhoenixxFire]

What is the reason for an increase in the rate of cellular respiration due to increasing oxygen concentration? Is it because since oxygen is the final electron acceptor, more water can be formed? But water is a waste product. Also, why does the rate of cellular respiration increase with oxygen concentration up to a certain point?

Yeah that's basically the reason. Rather than thinking about it as how much water can be formed, think about it as how much hydrogen can be accepted. Remember that the hydrogen ions power the ATP synthase, you need oxygen available to accept them otherwise that wouldn't work.

The rate of respiration increases because of the above, however if it is increased enough it becomes a limiting factor (increasing it more won't increase the speed of the reaction). When this happens it means that something else is limiting the rate of reaction - e.g. this could be carbon dioxide, enzyme concentration, or temperature. If you increase what is now limiting the reaction then the rate of reaction will start to increase again.

Is it correct that most eukaryotes and some microbes (yeast) undergo aerobic respiration, whereas most microbes perform anaerobic respiration, as well as skeletal muscle cells?

Thanks!

Sort of, there are a bunch of exceptions. e.g. there's plenty of bacteria that can do aerobic respiration. Also worth noting the yeast is a Eukaryote. You're not going to have to list which organisms use which type of respiration in the exam - if you need that information it'll be in the stem of the question somewhere or the question will specify whether oxygen is present.

[Larz_acccccccccccccccccccccc]

if enzymes are denatured, does this kill the cell itself?

[DBA-144]

if enzymes are denatured, does this kill the cell itself?

No, not necessarily. If the enzymes are denatured, this simply means that they cannot catalyse whatever reaction they previously did. Note that these may be essential processes eg. aerobic respiration that the cell can no longer carry out.

[PhoenixxFire]

No, not necessarily. If the enzymes are denatured, this simply means that they cannot catalyse whatever reaction they previously did. Note that these may be essential processes eg. aerobic respiration that the cell can no longer carry out.

In a practical sense, assuming extreme temperature & irreversible denaturation, the cell will die due to not being able to carry out these functions.

There's actually still a fair bit that's not really known about why proteins behave the way they do when facing heat stress, although this article discusses some of it if you're interested.

[DBA-144]

Is biomolecules; catabolic/anabolic reactions; induced fit/lock and key model; and biomechanical pathways of cellular respiration apart of the VCE Biology study design (2017-2021)
I am pretty sure that most of the concepts above is not on the current study design, however one of my SACs had all of the following concepts above.
Thanks 

Pretty sure that catabolic and anabolic is a part of the study design. It has come up in past VCAA exams as well. Pretty sure that this comes up under the notion of 'the role of enzymes as protein catalysts in biochemical pathways'- the main bit here is that a biochemical pathway may be either energy requiring (anabolic) or could be energy providing (what is that wording lol) this is catabolic.

Lock and key vs. induced fit is certainly in the study design. This describes the chemical nature of enzymes, i.e that the bonds that maintain the enzyme's specific 3D shape are not necessarily rigid (induced fit model's postulation). However, the lock and key model proposes that there is indeed no shape change in the enzyme throughout the reaction that it is catalysing. I think you can see here how the above 2 concepts are a part of the study design.

As for biochemical pathways in cellular respiration, it is not in the study desing (literally says that students do NOT need to know the details of the pathway). However, it depends to what depth your teachers assessed this; if they asked for inputs and outputs of the stages, that is certainly assessable, when aerobic respiration can/can't occur and the differences between anaerobic and aerobic respiration are definitely assessable. Most importantly- to what depth were the pathways assessed? given that you said biomechanical pathway, I assume you are referring to ATP synthase in the ETC? If so, I think that this is debatable whether or not this can actually be assessed, since it is not exactly 'detail' but I am pretty sure that it is not assessable.

Of course, your teachers are allowed to include whatever they wish to in your sacs, within reason.

I hope that this helps.

[f0od]

Are 2 ATP required to kickstart the breakdown of glucose in anaerobic respiration like aerobic respiration?

Thanks! 

[Erutepa]

Are 2 ATP required to kickstart the breakdown of glucose in anaerobic respiration like aerobic respiration?

Thanks! 

Yes, glycolysis requires an input of 2 atp but then produces 4 ATP. This means there is a net yield of 2 atp.

In vce bio, all you need to know is the net yield, not that it requires an input though.

[Chocolatemilkshake]

Hi everyone,

I'm wondering whether prokaryotic cells ever aerobically respire, or do they always use anaerobic respiration? In one of my school PPTs it states that the Krebs cycle and Electron Transport Chain can occur in the cytosol of prokaryotes. Is this wrong because I thought aerobic respiration needed the presence of mitochondria?

Thanks so much!

[DBA-144]

Prokaryotes definitely undergo aerobic respiration. Organisms who can also undergo anaerobic respiration are often also known as facultative anaerobes. If they always used anaerobic respiration, then they would be producing ethanol --> ethanol is toxic to cells --> cells die. Also note that whilst prokaryotes generally have fewer energy requirements, producing the 2 ATP produced in anaerobic respiration is NOT enough to maintain life. Note that archaic bacteria might have different pathways, but I am not sure about what they actually do. I am quite sure that this knowledge is outside of the study design though.


Mitochondria are only requirements in eukaryotic cells. The mitochondria provide the specific proteins required for aerobic respiration and have the internal environment to allow aerobic respiration to occur at its optimum rate. Also, note that this is achieved through the outer membrane which allows the internal environment of the mitochondria to be favourable to the conditions required by aerobic respiration. Interestingly, mitochondria were once independent organisms- these organisms used aerobic respiration as a source of energy. That is, that mitochondria were once prokaryotic cells that were engulfed by a eukaryotic cell (endosymbiosis theory). Hence, prokaryotes can certainly undergo aerobic respiration, just that they do not have mitochondria so the process occurs in the cytosol.

Hope this helps. If you have more questions, please ask them here!

[Chocolatemilkshake]

Prokaryotes definitely undergo aerobic respiration. Organisms who can also undergo anaerobic respiration are often also known as facultative anaerobes. If they always used anaerobic respiration, then they would be producing ethanol --> ethanol is toxic to cells --> cells die. Also note that whilst prokaryotes generally have fewer energy requirements, producing the 2 ATP produced in anaerobic respiration is NOT enough to maintain life. Note that archaic bacteria might have different pathways, but I am not sure about what they actually do. I am quite sure that this knowledge is outside of the study design though.


Mitochondria are only requirements in eukaryotic cells. The mitochondria provide the specific proteins required for aerobic respiration and have the internal environment to allow aerobic respiration to occur at its optimum rate. Also, note that this is achieved through the outer membrane which allows the internal environment of the mitochondria to be favourable to the conditions required by aerobic respiration. Interestingly, mitochondria were once independent organisms- these organisms used aerobic respiration as a source of energy. That is, that mitochondria were once prokaryotic cells that were engulfed by a eukaryotic cell (endosymbiosis theory). Hence, prokaryotes can certainly undergo aerobic respiration, just that they do not have mitochondria so the process occurs in the cytosol.

Hope this helps. If you have more questions, please ask them here!

Cool thanks so much it really does!