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AQA A2 Biology BIOL5 - 17th June 2015

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Original post by ACarter8
Anyone else absolutely screwed for this exam beacause of chem 5, C4 and biol 5 in consecutive days?! 😭😥😥😥😥


C4, Bio 5, Phy 5 for me :frown:
Original post by jf1994
C4, Bio 5, Phy 5 for me :frown:

I'll say a quick prayer for you
Original post by ACarter8
Anyone else absolutely screwed for this exam beacause of chem 5, C4 and biol 5 in consecutive days?! 😭😥😥😥😥


ME, it's killing me:ditto::goodluck:
anyone willng to explain IAA to me please?
Original post by sn4kebiteheart
anyone willng to explain IAA to me please?


IAA in the shoot of a plant will settle on the shaded side - where it causes cells to elongate faster than on the light side - so the shoot bends towards light (positively phototropic)

IAA in the root settles on the underside of the root due to gravity but here inhibit/slows down cell elongation (opposite to in the shoot) - this causes cells on top of the IAA concentrated region to elongate faster so the root bends down

:-) hope that helps
Anyone care to explain Restriction Mapping in english? This book makes zero sense and my revision has came to a halt
Original post by sn4kebiteheart
anyone willng to explain IAA to me please?


okay no one has replied so i guess i will explain :smile:
IAA is a substance produced in plants at their tips or in their roots. As a little bit of extra information IAA actually works alongside several other hormones in a plant such as cytokinins and gibberellins, but you don't need to know about these.
so in the tip of a plant IAA is produced and the hormone diffuses to the side of the plant that is shaded. the reason for this is because in the tip IAA causes elongation of the cells. as a result the cells on the shaded side grow more than the cells in the sun, which causes the tip to bend towards the light keeping all the leaves in the sunlight for maximum photosyntheses. we call this positive photo-tropism.

in the root tips the opposite occurs where the IAA moves to the lower side of the roots and prevents elongation of cells. the reason this happens is because IAA is working alongside a different hormone compared to in the plant tip. therefore the cells with little IAA present will elongate instead. for questions on root tips they will usually provide ample information and you can just apply what i have said.
i hope this makes sense :smile:
(edited 8 years ago)
I'm slightly confused as to what RNA polymerase does in transcription.

In replication DNA polymerase causes free nucleotides to bind with the template strand.

So does RNA polymerase just cause the free neucleotides to line up by complimentary bases of the template strand then attach the nucleotides to each other to form a single strand rather than attaching them to the template (which would them create a double strand so that doesn't make sense)...
Original post by jack1209
Anyone care to explain Restriction Mapping in english? This book makes zero sense and my revision has came to a halt


Ok so if you have a piece of unknown DNA, you can use the Sanger method of sequencing to find the DNA base order (using radioactively labelled terminator nucleotides/primers etc..) and then separate using electrophoresis and slowly piece the sequence together.
If however the DNA piece is really big then you have to break it into smaller fragments and sequence them individually. Once you've done that you need to put them back together in order; that's where restriction mapping comes in.
Using pairs of restriction enzymes allows you to work out where the recognition sequences are on the original piece of DNA by comparing the size of the DNA fragments that are produced on the electrophoresis. (They use the distance travelled by known samples to determine the size of the fragments).
Original post by shiney101
I'm slightly confused as to what RNA polymerase does in transcription.

In replication DNA polymerase causes free nucleotides to bind with the template strand.

So does RNA polymerase just cause the free neucleotides to line up by complimentary bases of the template strand then attach the nucleotides to each other to form a single strand rather than attaching them to the template (which would them create a double strand so that doesn't make sense)...


The free nucleotides bind to the template strand due to chemical gradients, it isn't the enzymes forming the hydrogen bonds (the nucleotides are 'attracted' to the exposed strand and join via complementary base pairing). The polymerase enzymes form the sugar-phosphate backbone by joining the nucleotides together, forming a strand.
Original post by shiney101
I'm slightly confused as to what RNA polymerase does in transcription.

In replication DNA polymerase causes free nucleotides to bind with the template strand.

So does RNA polymerase just cause the free neucleotides to line up by complimentary bases of the template strand then attach the nucleotides to each other to form a single strand rather than attaching them to the template (which would them create a double strand so that doesn't make sense)...


Rna polymerase synthesises the nucleotide strand DNA polymerase does the same the hydrogen bonds cause the template strand and the new strand in DNA to join together
Original post by Sheldon Cooper10
Rna polymerase synthesises the nucleotide strand DNA polymerase does the same the hydrogen bonds cause the template strand and the new strand in DNA to join together


Isn't pre-mRNA a single strand though? So if the two were to be joined together how are we getting a single strand?
anyone else feel like theyve not done enough work for this exam? wish there were more past papers on it as ive done the only five there is and its just not enough, i've planned all the essays from these exams and also an extra 5 from teacher predictions, i'm trying to review content but its just becoming more and more difficult
anyone got any revision tips? i've also listened to lots of youtube videos for biol5
for the essay weve been told to write the paragraphs as learn and churn, like the 6 marks at the back of unit 1 and 4, dont write it like a history/english essay and dont personalise it, also no conclusion
Original post by hiyaitsnikitaaa
anyone else feel like theyve not done enough work for this exam? wish there were more past papers on it as ive done the only five there is and its just not enough, i've planned all the essays from these exams and also an extra 5 from teacher predictions, i'm trying to review content but its just becoming more and more difficult
anyone got any revision tips? i've also listened to lots of youtube videos for biol5


If you're still looking for more past paper questions have a look at some of the relevant ones from the old specification
Original post by Ninainnarnia
If you're still looking for more past paper questions have a look at some of the relevant ones from the old specification

okay thanks i'll have a look and see what i can find
Original post by shiney101
Isn't pre-mRNA a single strand though? So if the two were to be joined together how are we getting a single strand?


when RNA polymerase attaches to the DNA double helix it binds to a specific DNA sequence called a promoter which is near the beginning of the gene.

So RNA polymerase attaches to the double helix which causes the hydrogen bonds between the DNA strands to break so DNA unocoils.

RNA polymerase lines up free nucleotides alongside template strand. specific base pairing means its complementary to the the DNA template (so they join together the nucleotides and the DNA). these nucleotides are joined together forming the pre- mRNA.
RNA polymerase moves down the DNA seperating the strands of mRNA and DNA which causes the hydrogen bonds within DNA to re form once RNA polymerase had passed by and becomes a double helix again. the pre-mRNA is therefore a copy of one strand of the DNA and is one strand itself.
which is then spliced and so on.

hope that made sense! :smile:
Can someone explain the difference between In vivo and in vitro. I understand how they work but when would you use each of them?
With PCR would you still have to isolate a DNA fragment using restriction endonucleases then will PCR just make many copies of it? What would be the point of doing that?

And with in vivo is it more about culturing a particular substance on large scale but using bacterial host cells etc and go through the whole isolation, insertion, identification etc to make sure the exact gene is obtained? eg: insulin
How in depth do we need to know about stem cells/stem cell therapy/bone marrow transplants?
Original post by shiney101
Can someone explain the difference between In vivo and in vitro. I understand how they work but when would you use each of them?
With PCR would you still have to isolate a DNA fragment using restriction endonucleases then will PCR just make many copies of it? What would be the point of doing that?

And with in vivo is it more about culturing a particular substance on large scale but using bacterial host cells etc and go through the whole isolation, insertion, identification etc to make sure the exact gene is obtained? eg: insulin


Essentially, yes. Both are forms of gene cloning, i.e. making mass copies of a single gene. Vitro does it by PCR, but vivo does it by bacterial mitosis (binary fission) so you get loads of plasmids with the single gene. With vivo you get the gene already in a vector, so you can use it to produce mass quantities of a particular protein. With PCR you just get lots of identical DNA which you can then use for something like genetic fingerprinting.

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