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!

                bioho4 Sadly, I haven't had any answers provided for me by my teacher either, which is frustrating. Sorry!

                  What is the significance that methionine isn’t present in any of the insulin polypeptides? (Insulin A/B) - like why do we specifically use methionine? Is it that if we used a different codon ex- the codon for Lys that’s lets say, present in the insulin A chain it would form part of the polypeptide and so we won’t be able to seperate the insulin A from beta galactosidase in the fission protein ?
                  Ahah just a lil bit confused on this- would be great if someone could give me an idea of what the reason is 🙂
                  Also to what depth do you guys reckon we should know the process of insulin production in humans? Like in terms of explaining the whole process for ex- for a 4/5 mark question? 🙂

                  Thanks so much!

                  hey! I've just been told that a lot of the resources - including textbooks and company summary notes - have incorrect information about the amount of ATP produced by aerobic cellular respiration because vcaa is now only accepting the amount that has been indicated to be true as per recent findings (changed from the 36-38). but they don't make it clear what these findings are.
                  do any of you know what the ATP yield we are now supposed to state for aerobic cellular respiration is?
                  thanks!

                    chimichurri You can find the new ATP yield information in the VCAA biology frequently asked questions document. This can be found with the biology study design web page under "Support - Planning".

                    The info specified on the document is as follows:
                    Glycolysis = 2 ATP
                    Krebs Cycle = 2 ATP
                    Electron Transport Chain = 26 or 28 ATP
                    Total = 30 or 32 ATP
                    (must say "or", not "-" for the new study design).

                    This information cannot be found in most textbooks due to VCAA having released the new info after they were written, I think, which is why there has been a lot of confusion.

                        Hey Guys!
                        I was wondering what is Lac Operon Model used to demonstrated?
                        what does it require?
                        And what does it produce?

                          yr12student22
                          My memory has faded - so I can’t remember the specifics (I can look up my old textbook if u want) - but I was under the impression they replaced it with a different operon… so this may he irrelevant as well as wrong… lol

                          Anyway - basically it’s a segment of DNA found in bacteria (which has three iirc gene coding regions). The gist of it was, they produce lactase (the enzyme) which broke down lactose.

                          However, when lactose is in a cell, some of it is converted into allolactose - the inducer. This molecule bound to the inhibitor (which was bound to the operator region located downstream of the promoter). This caused the inhibitor to no-longer fit the operator, and the coding regions could be transcribed / the enzyme produced.

                          Hence using a feedback loop. If the concentration of lactose got too high, more galactose would bind to the inhibitor - releasing it from the operator - and more enzyme would be made.

                          If the concentration was too low, less enzyme would be produced. (As more inducers bound to operators).hence less energy is wasted.

                            yr12student22
                            Just to add to this, the lac operon is no longer in the bio study design, as it has been replaced with the trp operon. However, they both do share similar principles.

                            What does the trp operon demonstrate?
                            It demonstrates the importance of gene expression regulation to aid in the conservation of energy and biochemical resources.

                            What does it require?
                            Not sure what you mean, but it involves the amino acid tryptophan. It also involves RNA polymerase, repressor proteins, ribosomes, and tRNA.

                            What does it produce?
                            When the structural genes are transcribed and translated, they form enzymes that convert different chemicals into tryptophan. This is what is specifically produced (don't need to know, but it can be helpful when understanding how it all 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)

                            Here is the trp operon order as well to make the above answer make more sense haha.
                            3' end - Promoter - Operator - Leader (TrpL) - Attenuator - TrpE - TrpD - TrpC - TrpB - TrpA - Trailer - 5' end

                            You do need to know about the two methods of gene expression regulation, which are repression and attenuation (I think the lac operon only involved a repression mechanism, but the trp operon involves the process of attenuation as well, which is more complex).

                              Hi there. I was wondering if anyone would be able to explain how CRISPR CAS 9 defence system works in bacteria.

                                does substrate bind to enzyme or enzyme binds to substrate?

                                how do we explain anaerobic respiration? and also why is producing atp important in respiration

                                6 days later

                                Does the tracrRNA bind to the palindromic sequence on the CRISPR sequence or on the crRNA?

                                BIOQ
                                In bacteria CRISPR acts as a defence system by recognising foreign viral DNA sequences and incorporating it into the bacteria’s CRISPR sequence/genome as a “spacer” upstream of the PAM. This occurs as cas9 is able to cut the viral DNA at a specific sequence of nucleotides (restriction site) complementary to the nucletides of the short guide RNA
                                This allows the bacteria to have a memory of past viral infections such that in future if the same virus invades, a faster, stronger, greater response is triggered as the cas9 rapidly cuts the viral DNA inducing a mutation in it and preventing it from replicating, hence preventing viral infection/spread in the bacterium. The PAM a sequence of nucletides downstream of the gene of interest in the virus which helps cas9 differentiate between the virus as a “non self” molecule and the bacterias own CRISPR genome as being “self”