VCE Biology Question Thread

[vox nihili]

Hi guys

Does DNA replication occur in the 5' to 3' direction. Is it opposite to the direction of DNA polymerase

The new strand is built in the 5' to 3' direction.


The way I remember it is to remind myself that polymerases read 3' to 5', just as I would read left to right and therefore the new strand must be made the opposite way 5' to 3'. Still use that now.

[Biology24123]

The human body is able to produce millions of different antibodies in response to the millions of different antigens

This is becuase:
a) The presence of a complete set of antibody genes in all B cells
b) The production of variable regions in the structure of antibodies due to rearranging of a few genes in their DNA

Which one is it and can you explain it please

[vox nihili]

The human body is able to produce millions of different antibodies in response to the millions of different antigens

This is becuase:
a) The presence of a complete set of antibody genes in all B cells
b) The production of variable regions in the structure of antibodies due to rearranging of a few genes in their DNA

Which one is it and can you explain it please

B. I can explain it, but you don't need to know for VCE at all.

[Biology24123]

B. I can explain it, but you don't need to know for VCE at all.

Was on a STAV exam

[vox nihili]

Was on a STAV exam

It shouldn't have been.

[Biology24123]

Phytochrome-deficient mutants of the plant Arabidopsis are unable to
a) Control their flowering b y detecting changes in day length
b) Carry out photosynthesis due to an an ability to absorb light
c)  Produce antibodies that kill bacteria and fungal pathogens
d) Seal wounds caused by grazing insect pests

Do we need to know this??

[heids]

Do we need to know this??

No.

[cosine]

I can't seem to find Polymerase Chain Reaction and other techniques like recombinant DNA on the study design. Are we meant to know these? If so, how much detail about PCR must we know? Thank you

[heids]

I can't seem to find Polymerase Chain Reaction and other techniques like recombinant DNA on the study design. Are we meant to know these? If so, how much detail about PCR must we know? Thank you

PCR = DNA amplification, you defs need it (was on our exam last year methinketh).
You only need something pretty basic:
1.  Heat DNA to ~90C to break hydrogen bonds between DNA strands.
2.  Cool to attach primers (short fragments of R/DNA, can't remember which).
3.  Reheat, taq polymerase copies strands, building off primers.
4.  Repeat process lots of times.

Recombinant DNA - I assume you mean recombinant plasmids and bacterial transformations?  If so, definitely it's on the SD.

[cosine]

PCR = DNA amplification, you defs need it (was on our exam last year methinketh).
You only need something pretty basic:
1.  Heat DNA to ~90C to break hydrogen bonds between DNA strands.
2.  Cool to attach primers (short fragments of R/DNA, can't remember which).
3.  Reheat, taq polymerase copies strands, building off primers.
4.  Repeat process lots of times.

Recombinant DNA - I assume you mean recombinant plasmids and bacterial transformations?  If so, definitely it's on the SD.

What is the main difference between PCR and recombinant plasmids? Obviously the steps undertaken are different, but what is the difference in the end result, and why would scientists choose PCR over recombinant plasmids, or the other way around? Don't they both replicate specific DNA fragments?

For recombinant plasmids and bacterial transformations, is this all we need to know:

1. Target DNA from a specific organism is isolated and cut using specific restriction enzymes
2. The same restriction enzymes are used to cut the vector/plasmid so that complementary sticky ends can be produced
3. The passenger-DNA is mixed with the vector/plasmid, and under the presence of DNA ligase, the phosphate backbones are covalently bonded together to form phosphodiester bonds. The passenger-DNA is now combined with the vector/plasmid
4. The plasmid/vector is inserted into a bacterial cell.
5. The plasmid/vector undergo replication and the shortly after the bacterial cells undergo binary fission
6. The required gene has now been replicated, multiple times. But this gene can only function if it is switched on.

[vox nihili]

What is the main difference between PCR and recombinant plasmids? Obviously the steps undertaken are different, but what is the difference in the end result, and why would scientists choose PCR over recombinant plasmids, or the other way around? Don't they both replicate specific DNA fragments?

For recombinant plasmids and bacterial transformations, is this all we need to know:

1. Target DNA from a specific organism is isolated and cut using specific restriction enzymes
2. The same restriction enzymes are used to cut the vector/plasmid so that complementary sticky ends can be produced
3. The passenger-DNA is mixed with the vector/plasmid, and under the presence of DNA ligase, the phosphate backbones are covalently bonded together to form phosphodiester bonds. The passenger-DNA is now combined with the vector/plasmid
4. The plasmid/vector is inserted into a bacterial cell.
5. The plasmid/vector undergo replication and the shortly after the bacterial cells undergo binary fission
6. The required gene has now been replicated, multiple times. But this gene can only function if it is switched on.

PCR is more reliable and waaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaay quicker and cheaper

[cosine]

PCR is more reliable and waaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaay quicker and cheaper

Cheers brah!

Also with restriction enzymes, why is it preferred that they cut the DNA fragment outside the desired gene? Is it because we want to isolate the gene and so we cut outside the gene?

What even is a gene? Is it just like a sequence of base pairs/DNA that codes for a specific protein?

[mahler004]

Cheers brah!

Also with restriction enzymes, why is it preferred that they cut the DNA fragment outside the desired gene? Is it because we want to isolate the gene and so we cut outside the gene?

What even is a gene? Is it just like a sequence of base pairs/DNA that codes for a specific protein?

You don't want to cut away any nucleotides that are involved in coding the protein you're interested in, yeah.

That's a reasonable definition of a gene (at least in a molecular sense.)

What is the main difference between PCR and recombinant plasmids? Obviously the steps undertaken are different, but what is the difference in the end result, and why would scientists choose PCR over recombinant plasmids, or the other way around? Don't they both replicate specific DNA fragments?

As far as actually generating/replicating/amplifying DNA (especially small DNA fragments,) PCR is much faster and easier (as T-Rav said.) PCR is often used in the generation of recombinant plasmids, and plasmids are used in a lot of applications that aren't DNA replication.

[Biology24123]

Are linked genes a big part of the study design

[Maca 13]

How much do we need to know about EcoRI? Would any questions appear on the exam in regards to this restriction enzyme without any background information in the question about it?
Thanks!