Psyxwar's Biology 3/4 Question Thread

[vox nihili]

AFIAK, yes, introns are always introns and are never included in the mature mRNA.
Alternative splicing to produce different isoforms of the same protein is achieved by using different combinations of exons, NOT introns.

By the way, when do we look at that stuff? First year or second? I know we did a little bit already with antibodies, but not to that extent obviously. Otherwise I missed it, which is completely possible...

[stonecold]

By the way, when do we look at that stuff? First year or second? I know we did a little bit already with antibodies, but not to that extent obviously. Otherwise I missed it, which is completely possible...

Umm, you will learn mRNA splicing in MCB next year I am pretty sure.
Alternative splicing is not really covered though.  I think it is mainly because it is not really known how it is regulated.
I also learned splicing in GENE20002 Genes and Genomes.

In BIOM30002, we learned about Duchenne Muscular Dystrophy and the Dystrophin gene which encodes Dystrophin, an important protein anchor in muscle cells.  This is an example of a gene/protein which has a few different isoforms which are due to alternative splicing IIRC.

[vox nihili]

Umm, you will learn mRNA splicing in MCB next year I am pretty sure.
Alternative splicing is not really covered though.  I think it is mainly because it is not really known how it is regulated.
I also learned splicing in GENE20002 Genes and Genomes.

In BIOM30002, we learned about Duchenne Muscular Dystrophy and the Dystrophin gene which encodes Dystrophin, an important protein anchor in muscle cells.  This is an example of a gene/protein which has a few different isoforms which are due to alternative splicing IIRC.

Ohh that sounds pretty cool!
I'm thinking I'll probably do genetics next year, so that's relevant.

Thanks for that!

[alondouek]

AFIAK, yes, introns are always introns and are never included in the mature mRNA.

Seconded. Introns are present in pre-mRNA, but are removed by the action of spliceosomes prior to the capping of the mature mRNA with a poly-A tail.

Introns are always introns in the sense that they do not have DNA sequences that code for final, specific protein products (although some intron sequences do encode specific proteins which are 'refined' to non-coding RNA molecules - but this is beyond the VCE curriculum).

[Yacoubb]

Seconded. Introns are present in pre-mRNA, but are removed by the action of spliceosomes prior to the capping of the mature mRNA with a poly-A tail.

Introns are always introns in the sense that they do not have DNA sequences that code for final, specific protein products (although some intron sequences do encode specific proteins which are 'refined' to non-coding RNA molecules - but this is beyond the VCE curriculum).

So just to clarify:

a A pre-mRNA molecule that has just been transcribed off DNA contains both introns and exons, introns being entire non-coding regions, whereas exons are entire non-coding regions. Introns are always introns in the sense that because they do not code for any particular amino acid at any time, they will always be spliced out of the mRNA molecule following post-transcription modification.

[Russ]

^^
Not as such. Introns aren't excised because they don't code for amino acids (they would if they were expressed), they're excised because they're not needed and have biochemical markers to trigger removal.

In VCE you can say that introns are always excised and never expressed and nobody will mark you down for it, the niche scenarios are basically irrelevant.

[vox nihili]

In the VCE course all you need to know is that pre-mRNA contains regions of RNA called introns and exons, and that during post transcriptional modification the intron regions are removed, and the exon regions will go on to code for a protein. This is the level of detail expected by the course.

[Scooby]

So just to clarify:

a A pre-mRNA molecule that has just been transcribed off DNA contains both introns and exons, introns being entire non-coding regions, whereas exons are entire non-coding regions. Introns are always introns in the sense that because they do not code for any particular amino acid at any time, they will always be spliced out of the mRNA molecule following post-transcription modification.

[Yacoubb]

Oops! That was a typo. Exons are entire coding regions!

[psyxwar]

Thanks guys. You guys sure stay up late lol

[vox nihili]

Thanks guys. You guys sure stay up late lol

What better to do at 2am than Biology?

[psyxwar]

Touche.

Also: what do we need to mention in hypotheses?

The STAV papers seem to have things like "that sucrose concentration affects the amount of mass gained or lost by the potato cube" or something. I was under the impression hypotheses need to specify direction (ie. increasing solute concentration increases mass loss). Am I allowed to just write something so general in the exam?

Also:

The answer they gave to the 2 mark question "Is there a control in this experiment? Explain:"

"There is no control as such but the various factors that need to be controlled are the amount of solution, the size and shape of potato cubes and the time left in solution."

How does that even work? Control =/= whether or not the experiment was valid.

Third edit: why do animals use both polysaccharide and lipids as an energy source whereas plants use only polysaccharide?

Would an answer about animals being mobile and therefore needing a more compact energy store (lipids, due to their higher energy/gram ratio) so they use lipids for long term storage and carbs for short, whereas plants do not need a compact store and therefore can just use the readily accessible polysaccharides?

The answer given by STAVs is that "plants have less energy needs, therefore can use complex carbs, whereas fats give more energy per gram and therefore animals use it for long term and carbs for short term". I'm not sure how that actually explains why animals don't just use carbohydrates exclusively though? There's no explanation for why compactness is preferred over more ready access.

^could someone help with these please?

[SocialRhubarb]

1. According to my biology teacher, the definition of a hypothesis is not unanimous. I think they'd allow for a little bit of variation.

2. A control usually refers to a specific group which has been set aside for the sole purpose of providing a reference point for other results. In your example of potatoes and concentration of sucrose, an example of a control would probably be a potato place in a solution with a sucrose concentration of 0. There is a difference between a control and controlling variables.

3. I think the point the answer is trying to emphasise is that animals require more versatility from their energy sources. Plants are generally exposed to the same environments all the time and thus their energy needs and do not vary greatly, whereas animals can quickly transition from a period of rest to a period of intense activity before returning to a period of rest, and therefore need more versatile methods of storing energy. That said, your answer is logical and it makes sense.

[vox nihili]

1. According to my biology teacher, the definition of a hypothesis is not unanimous. I think they'd allow for a little bit of variation.

2. A control usually refers to a specific group which has been set aside for the sole purpose of providing a reference point for other results. In your example of potatoes and concentration of sucrose, an example of a control would probably be a potato place in a solution with a sucrose concentration of 0. There is a difference between a control and controlling variables.

3. I think the point the answer is trying to emphasise is that animals require more versatility from their energy sources. Plants are generally exposed to the same environments all the time and thus their energy needs and do not vary greatly, whereas animals can quickly transition from a period of rest to a period of intense activity before returning to a period of rest, and therefore need more versatile methods of storing energy. That said, your answer is logical and it makes sense.

1. The fairly universal definition of a hypothesis is that is a statement of prediction about a population. You then use an experiment to either reject or accept that statement about the population. A good experiment is therefore one that allows you to do so.

2. Note that a control is the group where the experimental variable is absent. That is, there's no IV. It provides a reference point because of this. What would happen in "normal conditions". So if you're testing an enzyme, and there is actually something else that is doing what you think the enzyme would be doing, the control would show this. It's, like you said, a point of reference but you really need to emphasise the fact that the experimental condition is absent.

[psyxwar]

1. The fairly universal definition of a hypothesis is that is a statement of prediction about a population. You then use an experiment to either reject or accept that statement about the population. A good experiment is therefore one that allows you to do so.

So, in 3/4 Bio do you think something like "that x impacts y" is sufficient?

2. A control usually refers to a specific group which has been set aside for the sole purpose of providing a reference point for other results. In your example of potatoes and concentration of sucrose, an example of a control would probably be a potato place in a solution with a sucrose concentration of 0. There is a difference between a control and controlling variables.

Yeah I know, which is why the given answer didn't make any sense to me.

3. I think the point the answer is trying to emphasise is that animals require more versatility from their energy sources. Plants are generally exposed to the same environments all the time and thus their energy needs and do not vary greatly, whereas animals can quickly transition from a period of rest to a period of intense activity before returning to a period of rest, and therefore need more versatile methods of storing energy. That said, your answer is logical and it makes sense.

Yeah, but it doesn't explain why, just hint that it is the case. Oh well.