Re: Enzymes, _sophiestudies_ Answer is really good!

I’d suggest that we don’t really need to know anything more complex than this for VCE - but I think I know what you are talking about with the whole ‘bringing reactants together’.

I believe there is a khan academy video where he talked about the reaction between an Alkene and water. (An Alkene being a carbon chain with a Carbon=Carbon double bond in the middle)

The enzyme/catalyst moves or bends the hydrogens away from the double bond - allowing for the water molecule to attack it (performing a nucleophilic attack). This - without the catalyst - is harder; because the hydrogens would get in the way of the water molecule. This is called a hydration/addition reaction in Chem.

While you don’t need to know that for bio - I found it quite interesting last year.

Another example is that of ATP synthase. It acts like a windmill - using the flow of H+ ions to provide energy to attach a phosphate group to ADP - forming ATP.

So overall, perhaps:
An enzyme lowers activation energy by stimulating conditions favourable to the reaction - and weakening intramolecular forces.

      God Technically the acid catalyst is there to increase the electrophilicity of the electrophile (it allows the carbocation to actually form), otherwise there's no electrophile for water (nucleophile) to attack. The main goal is to remove turn that pi bond into a sigma C-H bond, if that pi bond is still there, it's nucleophilic and nucleophiles can't attack other nucleophiles

        Just to add to _sophiestudies_ reply. Though the study design states both an induced fit model or the lock and key model can be used to explain enzymes. Usually the induced fit model (in which the enzyme changes its shape to accommodate to the substrate because they're not perfectly complementary like the lock and key) receives more support for this exact reason. In the process of accommodating its shape to fit the substrate it stress the bonds (intramolecular) within the substrate and brings it to a state where it more favorable to react - hence decreasing the activation energy for the reaction.

            tubes yes, I absolutely agree with that! I was just trying to keep it as simple as possible haha. But yes, the induced fit model and lock and key model do slightly differ. The induced fit model does state that through the conformation change, the enzyme creates a chemical environment in the active site that is required for the reaction to proceed. It's important to note that that the way enzymes go about this can differ with the induced fit model. Some will speed up chemical reactions by bringing the substrate together in the right orientation. Some will alter the chemicals inside the active site to favour the reaction (e.g. polarity or pH). The substrate molecules can sometimes be bent to facilitate bond-breaking as well, etc. etc. After the reaction has occurred, the enzyme returns to its original state (unlike the "lock and key" model that states that there are no active site changes/conformation changes and that the substrate binds to it perfectly). However, the basic principles are still similar between both models; enzymes bind to reactant molecules and hold them in such a way that chemical-bond breaking and forming can occur more quickly, weakening the intramolecular forces holding the substrate together and bringing it/them into a state where a reaction is more favourable. Obviously, the process is much more complex, but from what my bio teacher has told me, these are the main principles to understand (also, VCE chem is much more detailed, as the chemistry behind how enzymes lower activation energy and reactions rates/catalysts are discussed in more depth, whereas this is not as prominent in the VCE bio study design from what I've been told -> It's the principles that are key!).

              theoretically, why does the rate of reaction of enzymes with unlimited substrates but limited non-competitive inhibitors still decrease significantly? wont the substrates out number the non-competitive inhibitor number and therefore the rate of reaction will continue to increase at a fairly steady rate?
              also, does the non-competitive inhibitor (after binding) leave the allosteric site ever? and if it does, will the active site of the enzyme return to its original state and ready to bind with the original substrate again?

                chimichurri I think it is probably because that the substrates can't actually 'outnumber' the non-competitive inhibitors as they aren't competing and bind to different sites.
                So if the concentration of enzymes is constant while the substrate's is unlimited, we know that the rate of reaction will plateau after a certain point, so when non-competitive inhibitors added, even though those may be in a limited quantity, the rate is likely to go down instead of increasing.
                I'm not too familiar with what happens after non competitive inhibition has occurred, but I found some information on sciencedirect.com that could be of use >> https://www.sciencedirect.com/topics/neuroscience/non-competitive-inhibition

                    Hi!
                    I was wondering if anyone knew how should one's responses differ when a question asks you to analyse the results of an experiment, as opposed to explaining them?

                    Hi guys- could someone please help explain Q13 (Multiple Choice) of the VCAA 2003 Exam 1 (sorry I don't really know how to add pictures on this like it dosent seem to be working for me)
                    The examiners report dosent have a marked answer.. Why wouldn't N be correct if the cell was undergoing anaerobic respiration? Wouldn't the alcohol levels increase with c02 as both are products of the reaction?
                    The examiners report says its not N
                    I think its P because even though the rate of co2 production is decrease, the amount is probs still increasing as the graph is in the positive axis right- so at point P when oxygen is introduced it undergoes aerobic cellular respiration and with this as the rate of production of co2 increases the alcohol levels would decrease.. thats why its not Q
                    Does my logic make sense? Basically im confused between point N and point P
                    so if someone could explain the concept behind how to think about this question thatd be great!
                    thanks so much!! 😃

                      Hello Smartiestarz!

                      Hi guys- could someone please help explain Q13 (Multiple Choice) of the VCAA 2003 Exam 1 (sorry I don't really know how to add pictures on this like it dosent seem to be working for me)
                      The examiners report dosent have a marked answer.. Why wouldn't N be correct if the cell was undergoing anaerobic respiration? Wouldn't the alcohol levels increase with c02 as both are products of the reaction?
                      The examiners report says its not N
                      I think its P because even though the rate of co2 production is decrease, the amount is probs still increasing as the graph is in the positive axis right- so at point P when oxygen is introduced it undergoes aerobic cellular respiration and with this as the rate of production of co2 increases the alcohol levels would decrease.. thats why its not Q
                      Does my logic make sense? Basically im confused between point N and point P
                      so if someone could explain the concept behind how to think about this question thatd be great!
                      thanks so much!! 😃

                      You are right, the answer is P because the question asks for concentration (amount) of alcohol, which is cumulative. If it asked for rate of alcohol production then the answer would be N instead, but that would be a different question altogether.

                        With competitive inhibition, the inhibitor is similar/complementary in shape to substrate? Is it complementary or similar?
                        Thanks

                          chemistry1111 yep. More specifically, the competitive inhibitor will have a very similar, if not the same, shape as the binding site on the substrate (the rest of it could be a very different shape). This is why it is able to bind to the enzyme's active site and prevent the substrate binding.

                            chemistry1111
                            Antigenic drift = Small and gradual mutations in the genes encoding for viral surface antigens.

                            • At first, the memory cells that were formed when the viral pathogen was previously encountered can recognise the mutated surface antigens.
                            • Over time -> The viral antigens gradually become very different, meaning the memory cells can no longer recognise them. This is when a new subtype of a virus is formed.

                            Antigenic shift = Sudden and significant mutations in the genes encoding for viral surface antigens.

                            • Commonly occurs when two or more different strains of a virus combine when coinfecting the same host to form a completely new subtype (this is quite a sudden change compared to small antigen changes on the surface of the virus). This process known as viral recombination.
                            • Natural immunity to this new subtype is very uncommon, meaning it is very infectious and able to potentially develop into an epidemic or pandemic.

                              hi there, does anyone have answers for the 2022 vcaa sample exam? if your teachers gave them to you or if you've seen them online cos i cant find any answers for section B. thanks in advance!!!

                                bioho4 VCAA doesn't seem to provide answers for any of their sample exams (well, nothing that involves short answer responses that is). You might need to ask your teacher if they have an answer document for it (as in, one they have put together themselves). It's quite annoying, especially since it's the only VCAA exam material given for this new study design.

                                    Neap or insight or someone wouldn't have made their own sample answer's would they?

                                    I vaguely remember checkpoints containing last (last) years's exam with sample answers. Although I could be wrong. (Perhaps it was just copied from the exam report)

                                      _sophiestudies_ it is very very annoying - not sure why they don't provide sample answers. my teachers haven't provided any. if you're teachers have it'd be great if you could send it through!