VCE Biology Question Thread

[katiesaliba]

Another question about the liver prac (already completed a couple days ago so I'm not cheating or anything ). A question asked us to discuss the induced fit model and provide a diagram (1 mark). In class my teacher had mentioned that the induced fit model suggests that while enzymes are still highly specific they can lower their specificity for similar shaped substrates. I wasn't sure whether or not to mention this (I did) and I'm hoping I didn't throw the mark away. Is this true or was I just dreaming it up

Enzymes don't lower their specificity - their active sites are specific to a substrate. The induced fit model relays that, upon enzyme-substrate complex formation, the conformations of both the enzyme and the substrate will slightly change as to enable a perfect fit. Therefore, specifically is never reduced, rather affinity is increased.

[blacksanta62]

Mr T-Rav: What I meant was that a given enzyme can take on a wider variety of substrates which are kind of the same. So with the lock and key model, one enzyme to one substrate. But with the induced fit model, one enzyme similiar typed substrates since it can mold it's active site to better fit it.

 katiesaliba: Was this a mark thrown away??

[katiesaliba]

Mr T-Rav: What I meant was that a given enzyme can take on a wider variety of substrates which are kind of the same. So with the lock and key model, one enzyme to one substrate. But with the induced fit model, one enzyme similiar typed substrates since it can mold it's active site to better fit it.

 katiesaliba: Was this a mark thrown away??

I would assume so. What you've described is not the reasoning behind the induced fit model. The induced fit model does not necessarily contend that a single enzyme may have multiple substrates - it proposes an increase in enzyme-substrate affinity upon binding.

Think about it this way: an active site is made up of a specific sequence of amino acid residues because enzymes are protein-based. This sequence will therefore be highly specific to a given substrate. Simply looking at pictures of the process can make enzymes look more flexible than what they actually are! I hope this elucidates things a bit more

[blacksanta62]

Okay. Won't mix that up at all next time and if I'm not to sure about something I will not use it as an answer next time . Thank you

[johnhalo]

I was wondering if someone could explain the graphs of the limiting factors of photosynthesis, involving light intensity, carbon dioxide and temperature. I don't know how to fully explain it, but understand the basic details of it.

Thanks

[vox nihili]

Enzymes don't lower their specificity - their active sites are specific to a substrate. The induced fit model relays that, upon enzyme-substrate complex formation, the conformations of both the enzyme and the substrate will slightly change as to enable a perfect fit. Therefore, specifically is never reduced, rather affinity is increased.

Avoid the term perfect fit. It isn't perfect, it's just better because of induced fit.

(that's the VCE knowledge anyway, in truth it's not reallllly like that)

Mr T-Rav: What I meant was that a given enzyme can take on a wider variety of substrates which are kind of the same. So with the lock and key model, one enzyme to one substrate. But with the induced fit model, one enzyme similiar typed substrates since it can mold it's active site to better fit it.

 katiesaliba: Was this a mark thrown away??

Yep, that's right then.


It's probably a bit silly that they teach you lock-and-key at all to be honest. Lock-and-key is simply not an explanation for the interaction between enzyme and substrate. Indeed, introducing you to induced fit exposes all of the flaws in lock-and-key as a model. Yet for some stupid reason they still teach it. Then 90% of students fixate on lock-and-key as an explanation of how enzymes work, when it's not how they work...

[blacksanta62]

Hey T-Rav, I'm a bit confused. What's right, my explaination or the mark being thrown away? And how's the MD course at UoM? Just saw it on your Signature.
Note: Not trying to derail the thread by asking that question

Edit: In photosynthesis, in particular the light dependent reaction side, does the splitting of 6H2O(l) works with this equation:

6H2O(l) -------> 12H^+(aq) + 6O^2-(aq) ?

Another question I have is do the O^2-(aq) ions join with other O^2-(aq) ions to form 6O2(g)? Just a bit curious to find out how the O2(g) is formed though I presume this is how .

Thank you

[Gogo14]

I was wondering if someone could explain the graphs of the limiting factors of photosynthesis, involving light intensity, carbon dioxide and temperature. I don't know how to fully explain it, but understand the basic details of it.

Thanks

Light intensity: log shaped graph, the rate increases slower when there is more light as there is not enough reactants.
CO2: log shaped graph, the rate increases slower when there is more CO2 because water and light are limiting factors
Temp: like the enzyme temperature graph, becauses there are enzymes which carry out reactions in photosynthesis

[vox nihili]

Hey T-Rav, I'm a bit confused. What's right, my explaination or the mark being thrown away? And how's the MD course at UoM? Just saw it on your Signature.
Note: Not trying to derail the thread by asking that question

Edit: In photosynthesis, in particular the light dependent reaction side, does the splitting of 6H2O(l) works with this equation:

6H2O(l) -------> 12H^+(aq) + 6O^2-(aq) ?

Another question I have is do the O^2-(aq) ions join with other O^2-(aq) ions to form 6O2(g)? Just a bit curious to find out how the O2(g) is formed though I presume this is how .

Thank you

Your explanation was perfect. A good way of thinking of things, but not something I'd be inclined to mention on the exam. Remember, there is no extra credit for knowing things outside the course or showing off, so stick to what you know is definitely related.

That's not to say you shouldn't avoid learning things, that's the fun of it after all

MD is gruelling, but interesting at the same time!

[blacksanta62]

Great to hear that it's a challenge but you pick something up after each session (not sure if they're sessions in Uni though). I've been told that it's more rote learning than application, to what extent do you agree with this. Feel free to reroute to an appropriate section if it's off topic
I've had that problem (not much of a problem unless it's costing me marks lol) since I've been little, always telling more than what's required. Just like sharing what I pick up it seems but I stick to the point when answering ( ..)

If possible could you please see the equation in my earlier post and correct where necessary.

[vox nihili]

Great to hear that it's a challenge but you pick something up after each session (not sure if they're sessions in Uni though). I've been told that it's more rote learning than application, to what extent do you agree with this. Feel free to reroute to an appropriate section if it's off topic
I've had that problem (not much of a problem unless it's costing me marks lol) since I've been little, always telling more than what's required. Just like sharing what I pick up it seems but I stick to the point when answering ( ..)

If possible could you please see the equation in my earlier post and correct where necessary.

There's a med school life discussion thread somewhere around, that's the best place for that question
I had that problem too. Solving it was a big part of doing well for me to be honest.

As for your equation, not quite I don't think. It's not really useful to think of how to balance that particular part of the system. The overall equation is as follows:

12H₂O+6CO₂—>6H₂O+6O₂+glucose

As for the splitting of water, it is usually represented as such:

H₂O—>2H⁺+1/2O₂

Note that the protons are aqueous and that the O₂ is gaseous, not an ion.

EDIT: gave a shockingly wrong answer the first time, sorry!

[johnhalo]

Sorry about asking so many questions lately. I'm just having a hard time nailing the intricate details of photosynthesis and cellular respiration. I came across some past exam questions and I'm having a hard time answering this one. I would love it if you could provide me with an answer to it.

Thanks

[Sine]

Sorry about asking so many questions lately. I'm just having a hard time nailing the intricate details of photosynthesis and cellular respiration. I came across some past exam questions and I'm having a hard time answering this one. I would love it if you could provide me with an answer to it.

Thanks

d(i) The amount of CO2 produced via Cellular respiration is equal to the amount of CO2 used up in photosynthesis.(compensation point)

d(ii) The plant is being subjected to a limiting factor other than light intensity. e.g Temperature,CO2 avaliabilty,water avaliability

[cosine]

Sorry about asking so many questions lately. I'm just having a hard time nailing the intricate details of photosynthesis and cellular respiration. I came across some past exam questions and I'm having a hard time answering this one. I would love it if you could provide me with an answer to it.

Thanks

At the beginning of the graph, the net production of CO2 is -5 arbitrary units, this means that the leaf was actually consuming/using up more CO2 from its environment than it was producing/releasing into it. This is because of a high rate of photosynthesis, as an input of this process is CO2. However, at point M, the net production of CO2 is 0. This means that the production of CO2 and the consumption of it is equal, so the rate of CO2 production via cellular respiration and the consumption of CO2 via photosynthesis is equal.

The graph line becomes nearly horizontal from about 600 units of absorbed light, despite the light intensity increasing may be due to the saturation of chlorophyll or it could be because the rate of water transport to the chloroplast has reached plateau, either way, the production of CO2 has become constant because there is a limiting factor that prevents the production of CO2 to increase further.

[Photon]

Does the oxidization of water molecules in photosynthesis require enzymes? Thanks