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Edexcel A2 Biology exams (6BIO4) 25th January 2012 exam discussion

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Reply 140
Avatar for Fardip
Fardip
Original post by This Honest
It's not really a practical, it's a stage in DNA profile

1) dna sample mixed with dna polymerase, primes and nucleotides
2) sample heated to 95 degrees to break the bonds in the dna strand
3) sample cooled to 65 degrees to allow the primers at the start of the dna strand to bind (anneal) to the strand
4) sample heated again to around 70 degrees to allow the dna polymerase to work and bind free nucleotides to dna strand via complementary base pairing

this will produce 4 copies of dna strands and the process starts again

sorry, if i'm not 100% correct, i'm trying to recite this from memory :emo:


Wow thanks man, that's good. I don't really get the DNA primers thing, What's their function in the stage. The book defines DNA primes as short sequences of DNA complementary to the DNA adjacent to the STR.

You're smashing it man, you'll merk the exam! :wink:
Original post by Fardip
Wow thanks man, that's good. I don't really get the DNA primers thing, What's their function in the stage. The book defines DNA primes as short sequences of DNA complementary to the DNA adjacent to the STR.
You're smashing it man, you'll merk the exam! :wink:


My cgp book says the exact same thing apart from the STR thingy, i'm not sure what they do?

and thanks, i don't want to get too confident :wink:
Reply 142
Avatar for Fardip
Fardip
Original post by This Honest
My cgp book says the exact same thing apart from the STR thingy, i'm not sure what they do?

and thanks, i don't want to get too confident :wink:


I just found out from youtube, the primers direct the DNA polymerase and label the section of the DNA to be amplified i.e. Target DNA. I dunno if we have to learn it.. :s-smilie:

Another question, when you repead the cycle, and go to stage one where you put the tubes into 95C degrees, don't you denature all the DNA you just made?!
Original post by Fardip
I just found out from youtube, the primers direct the DNA polymerase and label the section of the DNA to be amplified i.e. Target DNA. I dunno if we have to learn it.. :s-smilie:

Another question, when you repead the cycle, and go to stage one where you put the tubes into 95C degrees, don't you denature all the DNA you just made?!


all i know is that it's heated to 95C to break the hydrogen bonds between the 2 strands
Original post by Fardip
I just found out from youtube, the primers direct the DNA polymerase and label the section of the DNA to be amplified i.e. Target DNA. I dunno if we have to learn it.. :s-smilie:

Another question, when you repead the cycle, and go to stage one where you put the tubes into 95C degrees, don't you denature all the DNA you just made?!


Yup. you start with 1 piece of double stranded, after first cycle you have two pieces. Separate these 2 double stranded pieces in step 1, then the res tof the cycle means you get 4 lots of double stranded DNA
Reply 145
Avatar for aym3n
aym3n
Original post by Cleoleo
Thank you !!! :biggrin:


no problemo :wink:
As far as practicals go, which are the ones that we need to know? In my revision guide only pcr, electrogelphoresis and the antimicrobial one are mentioned, (besides Quadrat sampling etc)

Could there be a question on setting up an experiment measuring rate of photosynthesis? My teacher gave us questions on it, but it's not in the guide and I can't find it on the spec.
Reply 147
Avatar for Bright
Bright
11
Anyone retaking unit 2 and have access to past papers? (June 2011)
Reply 148
Avatar for Fardip
Fardip
Original post by Neopolitan Girl
As far as practicals go, which are the ones that we need to know? In my revision guide only pcr, electrogelphoresis and the antimicrobial one are mentioned, (besides Quadrat sampling etc)

Could there be a question on setting up an experiment measuring rate of photosynthesis? My teacher gave us questions on it, but it's not in the guide and I can't find it on the spec.


Your missing one out, The brine shrimp one..

The effect of temperature on hatching of brine shrimp eggs. You shoulda done this in school, I did, and it failed epicly, every shrimp died.. LOL :colondollar:
Original post by Fardip
Your missing one out, The brine shrimp one..

The effect of temperature on hatching of brine shrimp eggs. You shoulda done this in school, I did, and it failed epicly, every shrimp died.. LOL :colondollar:


Oh yeah, and that one. So it's just those 4?

Most of our shrimp died, one or two grew huge and the teacher put them all in a big fish bowl type thing. I don't know if they've survived over christmas though D:
Original post by Fardip
Your missing one out, The brine shrimp one..

The effect of temperature on hatching of brine shrimp eggs. You shoulda done this in school, I did, and it failed epicly, every shrimp died.. LOL :colondollar:


to my surprise, our class did all right, only 1 guy had full house of dead shrimps
Reply 151
Avatar for Fardip
Fardip
Original post by Neopolitan Girl
Oh yeah, and that one. So it's just those 4?

Most of our shrimp died, one or two grew huge and the teacher put them all in a big fish bowl type thing. I don't know if they've survived over christmas though D:


Yep, as far as i know, it's them 4. Brine shrimps hasn't come up recently, just like the PCR.. And in June 11, it was gel electrophoresis which came up..

lol All of them in our class layed around the bottom.. LOL

We also did the effect of temperature on maggots becoming a pupa.. Dunno if that was compulsory.. :s-smilie:
Hey, does someone have a good definition for allele frequency? Thanks :smile:
Reply 153
Avatar for Shippy
Shippy
11
no one even know what happened to our shrimp, we forgot to visit them outside of class and our teacher never told us what they ended up like!
Reply 154
Avatar for Fardip
Fardip
Original post by pabloishere
Hey, does someone have a good definition for allele frequency? Thanks :smile:


Allele Frequency: Number of times an Allele occurs at a gene pool. :biggrin:
Original post by Fardip
Yep, as far as i know, it's them 4. Brine shrimps hasn't come up recently, just like the PCR.. And in June 11, it was gel electrophoresis which came up..

lol All of them in our class layed around the bottom.. LOL

We also did the effect of temperature on maggots becoming a pupa.. Dunno if that was compulsory.. :s-smilie:


Oh for gods sake. We'll get collectively yelled at as a year group if our jan module results are pants, yet we haven't done ANY of the core practicals, and being a visual learner, doing them WOULD be helpful, but no, we've done the potato & H2O2 practical again. -_-
Original post by .snowflake.
Oh for gods sake. We'll get collectively yelled at as a year group if our jan module results are pants, yet we haven't done ANY of the core practicals, and being a visual learner, doing them WOULD be helpful, but no, we've done the potato & H2O2 practical again. -_-


They made us do that one again too, except we had to design it ourselves (by looking through last year's notes and going online...) to practice for Unit 6.

We've done loads of other irrelevant practicals, chromatography on photosynthetic pigments, the Winkler test, I don't mind but we rushed to finish the theory work then.

We did get to do PCR and a few gel electrophoresis, which was good.

The brine shrimp we did is different from the one in my book (CGP, OCR, AQA & Edexcel spec), we didn't bother with different temperatures at all, or measuring hatch rates.

There's another one in the book on the effect of temperature about seedling growth and temperature that I haven't seen anywhere else.
Original post by Fardip
I just found out from youtube, the primers direct the DNA polymerase and label the section of the DNA to be amplified i.e. Target DNA. I dunno if we have to learn it.. :s-smilie:

Another question, when you repead the cycle, and go to stage one where you put the tubes into 95C degrees, don't you denature all the DNA you just made?!


yes u r completely right we DO denature all the DNA v just made , but when we lower the temperature and complementary strands are made the previously formed DNA will also now make a complementary strand so we will get an even bigger amount of DNA because of so many complementary strands being made... u gettin me ?!:smile:
Original post by pabloishere
Hey, does someone have a good definition for allele frequency? Thanks :smile:


the probability of finding a particular allele in a gene pool !:smile:
PLEASE can someone tell me southern blotting stuff !! it so damn difficult !! i always confuse it with gene probes

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