VCE Biology Question Thread

[vox nihili]

Thank you so much:)

Can you answer my theory of gel electrophoresis please? What do you mean by the size of fragments and not their identity, because if two lanes has different sized fragments, then does that not imply that they were two different people because if it was the same person, it would obviously have the same sized fragments? o.o

Also for question 10 b (attached) the answer says that the woman would not be able to reproduce because her X chromosome would not be able to pair up with another sex chromosome. I dont really understand this, because can't meiosis occur even though there is a missing chromosome? I thought that because there is that one missing sex chromosome, then the baby has a higher chance of receiving a less chromosome (monosomy).

Well no. There's nothing in the question that tells you where the samples have come from, so you can't make any conclusions about the identity of the samples themselves. All you can see is a bunch of bands on a gel. You've got no idea where those bands are from. Therefore, you can only make conclusions about the relative sizes of the bands. You can't say anything more because you're not sure what they're from.

I think the best demonstration of that is that the question tells you that the gel has DNA in it, but it actually doesn't. I'd say with some confidence that that isn't actually a gel used to separate DNA, but protein instead.

You're probably all aware of the new hominin species found a couple weeks ago, Homo naledi. I was reading up on its Wikipedia page and came across this:

(Image removed from quote.)

So the bones were just loosely spread along the cave and weren't covered by sediment.. wouldn't they just have decayed over the long periods of time they were there for?

You'd think so. There are some very, very special environments though that just work out. I'm so, so, so glad you asked this question though. What a champ actually bringing in real life content.

Can someone explain to me simply how apoptosis works? All i know is that it's a programmed cell death that removes cancer/old cells.

What's a transitional fossil?

Cell fucked leads to cell kills itself. That's basically apoptosis. Old, damaged cells activate factors that essentially kill the cell from the inside.
In some cases, external signals can also activate apoptosis

[chemzy]

Hey guys!
Anyone, pls help with these clarifying questions!   

1. What is the difference between STRs and VNTRs and where are they located in DNA?

2. Is it the RNA polymerase that breaks the hydrogen bonds between complementary nucleotides in DNA during transcription?

3. When writing the code for mRNA, is it the DNA coding/ template strand or non Coding strand that we use? Pretty sure it's the coding strand.

4.  If a chromosome had two centromeres, why would inactivating one centromere allow for gamete production? Is it because it reduces the errors when the chromosomes are segregating towards the opposite poles?

5. Why STRs are mainly located in the telomeres of chromosomes?

Thanks for the help guys 

[Bruzzix]

You'd think so. There are some very, very special environments though that just work out. I'm so, so, so glad you asked this question though. What a champ actually bringing in real life content.

Thanks :3. What kind of conditions wouldn't favour bone degradation though, in what I'm assuming is an aerobic environment?

[thettywetty]

Hey guys!
Anyone, pls help with these clarifying questions!   

1. What is the difference between STRs and VNTRs and where are they located in DNA?
In introns. I believe VNTR's are longer than STRs, not too sure though...

2. Is it the RNA polymerase that breaks the hydrogen bonds between complementary nucleotides in DNA during transcription?

yes
3. When writing the code for mRNA, is it the DNA coding/ template strand or non Coding strand that we use? Pretty sure it's the coding strand.
no, its the template strand

4.  If a chromosome had two centromeres, why would inactivating one centromere allow for gamete production? Is it because it reduces the errors when the chromosomes are segregating towards the opposite poles?
Why would one chromosome have two centromeres?

5. Why STRs are mainly located in the telomeres of chromosomes?
Sorry, don't know, though we don't need to know about telomeres

Thanks for the help guys 
No, thank you

[thettywetty]

Can someone explain to me simply how apoptosis works? All i know is that it's a programmed cell death that removes cancer/old cells.

What's a transitional fossil?

A transitional fossil is a fossil that acts as an intermediate between forms.
ie. We have two different species A and C, each having their own fossils respectively. and then one day BAZINGA, we find fossil B, which is an intermediate between the two species. it is a transitional fossil

[BakedDwarf]

A transitional fossil is a fossil that acts as an intermediate between forms.
ie. We have two different species A and C, each having their own fossils respectively. and then one day BAZINGA, we find fossil B, which is an intermediate between the two species. it is a transitional fossil

Thanks Sheldon.

[thettywetty]

Thanks Sheldon.

You're welcome

[vox nihili]

Hey guys!
Anyone, pls help with these clarifying questions!   

1. What is the difference between STRs and VNTRs and where are they located in DNA?

2. Is it the RNA polymerase that breaks the hydrogen bonds between complementary nucleotides in DNA during transcription?

3. When writing the code for mRNA, is it the DNA coding/ template strand or non Coding strand that we use? Pretty sure it's the coding strand.

4.  If a chromosome had two centromeres, why would inactivating one centromere allow for gamete production? Is it because it reduces the errors when the chromosomes are segregating towards the opposite poles?

5. Why STRs are mainly located in the telomeres of chromosomes?

Thanks for the help guys 

Each of these questions are well outside of the VCE course.

1. Length. VNTRs are longer than STRs. They're located all round, though there are some areas with more like the ends of the DNA and around the centromere.

2. No. A helicase does.

3. Yes, it's the coding strand. Though in VCE it's called the template strand.

4. If a chromosome has two, though don't break apart. So you get one gamete with an extra chromosome and get another gamete with one less chromosome. This usually results in the death of the zygote. In the case of chromosome 21, an extra chromosome results in Down syndrome

5. Because with each division, the telomeres get shorter and shorter. So if genes were located at the telomeres, those genes would eventually cease functioning because the shortening of the telomeres chews them up. As a consequence of this, there's a lot of "junk" DNA at the telomeres.

[chemzy]

Thank you 'thettywetty' and 'Mr. T-Rav' for your answers! I really appreciate it.
Yeah, though it was outside the VCE course, I just thought it would make more sense to
fill in my gaps.
Can someone please explain to me the difference between all these terms and how they fit into transcription?
- coding strand, template strand, non coding strand, sense strand and anti sense strand
And which one RNA polymerase uses to synthesise mRNA?
Thanks you.

[cosine]

Thank you so much:)

Can you answer my theory of gel electrophoresis please? What do you mean by the size of fragments and not their identity, because if two lanes has different sized fragments, then does that not imply that they were two different people because if it was the same person, it would obviously have the same sized fragments? o.o

Also for question 10 b (attached) the answer says that the woman would not be able to reproduce because her X chromosome would not be able to pair up with another sex chromosome. I dont really understand this, because can't meiosis occur even though there is a missing chromosome? I thought that because there is that one missing sex chromosome, then the baby has a higher chance of receiving a less chromosome (monosomy).

Can someone help out on this one please?

[nhienhien852]

2. No. A helicase does.

I may be wrong. But I thought DNA helicase only unwind the DNA during DNA replication, whereas during transcription the DNA polymerase will bind to the promoter and separate the DNA strands?

[cosine]

I may be wrong. But I thought DNA helicase only unwind the DNA during DNA replication, whereas during transcription the DNA polymerase will bind to the promoter and separate the DNA strands?

DNA helicase unwinds DNA molecules, whether during DNA replication, RNA synthesis or whatever, whenever there is a molecule of DNA to be separated into its constituent strands, DNA helicase is used. Also I think what you have concluded about polymerase is wrong, but I am not sure (new to this topic). I think its actually RNA polymerase that is used during the transcription of the pre-mRNA molecule, because thats what is used to synthesise RNA, whereas DNA polymerase, as the name suggests, synthesises DNA molecules.

[vox nihili]

I may be wrong. But I thought DNA helicase only unwind the DNA during DNA replication, whereas during transcription the DNA polymerase will bind to the promoter and separate the DNA strands?

Nah it actually requires a helicase. The helicase is a transcription factor called TFIIH.

[Bruzzix]

"After recent analysis of human mtDNA, it has been concluded that all Europeans are descended from 200 people or less. This could be an example of"
A. genetic drift
B. a population bottleneck
C. natural selection
D. allopatric speciation

I didn't really like any of the answers and picked D but it turns out that B is the correct answer. I don't understand how this is a population bottleneck since there was no large reduction in the size of the population?

[Biology24123]

"After recent analysis of human mtDNA, it has been concluded that all Europeans are descended from 200 people or less. This could be an example of"
A. genetic drift
B. a population bottleneck
C. natural selection
D. allopatric speciation

I didn't really like any of the answers and picked D but it turns out that B is the correct answer. I don't understand how this is a population bottleneck since there was no large reduction in the size of the population?

Yeah I would have said B. A is technically right since a bottleneck is a type of genetic drift