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Edexcel A2 Biology SNAB 6BI04 ~ 6BIO5 June 2016

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Original post by Ladymusiclover
Yeah they're produced before PCR. The whole point of PCR is to make loads of genes from a tiny DNA Sample e.g. a speck of blood at a crime scene.
Also the sample of DNA is collected then cut up using restriction enzymes before gel electrophoresis takes place.


right, but why is the DNA cut up before PCR? to get specific STRs? but surely thats what PCR does?
Original post by mechanism
right, but why is the DNA cut up before PCR? to get specific STRs? but surely thats what PCR does?


The DNA strands are cut for gel electrophoresis in order to produce the DNA bands as the different cut DNA fragments move towards the positive anode at different speeds dependent on their charge and size etc. In PCR the strands are separated in order for the primer to anneal to one strand in order to produce a full DNA strand from a small sample.
So basically they're cut to produce the DNA bands in order to see the genetic differences or similarities between samples from gel electrophoresis. PCR has a different role than gel electrophoresis as it's is in order to make a large sample of DNA from a small sample.
Original post by mechanism
right, but why is the DNA cut up before PCR? to get specific STRs? but surely thats what PCR does?


I'm pretty sure that cutting DNA into fragments using restriction enzymes and amplifying a target sequence in PCR are just two different ways to generate DNA fragments for use in gel electrophoresis? I don't think you use PCR and restriction enzymes at the same time, I could be wrong though I haven't revised unit 1 in a while

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Original post by Ladymusiclover
The DNA strands are cut for gel electrophoresis in order to produce the DNA bands as the different cut DNA fragments move towards the positive anode at different speeds dependent on their charge and size etc. In PCR the strands are separated in order for the primer to anneal to one strand in order to produce a full DNA strand from a small sample.
So basically they're cut to produce the DNA bands in order to see the genetic differences or similarities between samples from gel electrophoresis. PCR has a different role than gel electrophoresis as it's is in order to make a large sample of DNA from a small sample.


Oh amazing I get it now! So you have already created bands for comparison before PCR, PCR just creates a large sample so it can actually be visualised. Thank you so much!
Original post by LThomas694
I'm pretty sure that cutting DNA into fragments using restriction enzymes and amplifying a target sequence in PCR are just two different ways to generate DNA fragments for use in gel electrophoresis? I don't think you use PCR and restriction enzymes at the same time, I could be wrong though I haven't revised unit 1 in a while

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o. ok thanks!
Original post by mechanism
Oh amazing I get it now! So you have already created bands for comparison before PCR, PCR just creates a large sample so it can actually be visualised. Thank you so much!


Yes PCR is just for amplification of the DNA sample. :h:
Reply 186
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JP 98
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Has anyone made any pre-release questions for the unit 5 article yet?
Just bought the potential questions and answers from Edexcel biology solutions :h:
Original post by A-LJLB
Just bought the potential questions and answers from Edexcel biology solutions :h:


bought? what? :colonhash:
Original post by genevievelaw
bought? what? :colonhash:


Yeah, you pay for them.
Original post by A-LJLB
Yeah, you pay for them.


Ah ok, I just looked them up :smile: Don't think I can do that, will have to come up with others :colondollar:
Original post by genevievelaw
Ah ok, I just looked them up :smile: Don't think I can do that, will have to come up with others :colondollar:


Haha yeah I bought the more expensive downloadable one for a few of my friends too but it is a little pricey, but I need all the help I can get! :P
Original post by A-LJLB
Haha yeah I bought the more expensive downloadable one for a few of my friends too but it is a little pricey, but I need all the help I can get! :P


Are they good? Also you should've just bought the Read only copy and then give your friends access to the account that way you save 70 euros :/
Original post by BrownGuyIrfan
Are they good? Also you should've just bought the Read only copy and then give your friends access to the account that way you save 70 euros :/


I didn't want them to have access to my account. Also, I like having printed versions so I can revise wherever I am. Yeah they cover the basics and have model answers.
Original post by A-LJLB
I didn't want them to have access to my account. Also, I like having printed versions so I can revise wherever I am. Yeah they cover the basics and have model answers.


What website is this?

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edexcel biology solutions
Hi guys! I'm thinking about making a WhatsApp for those taking Edexcel biology. Will be good to post any questions and clear any doubts about anything. We can also talk about pre-release :tongue:

PM me if you want in
Reply 197
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Neuth
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Original post by ultimatesword
Hi guys! I'm thinking about making a WhatsApp for those taking Edexcel biology. Will be good to post any questions and clear any doubts about anything. We can also talk about pre-release :tongue:

PM me if you want in


I already have a Skype group for this! There are 11 of us on it :fluffy:
Hey everyone,
Could someone please explain phytochromes -as in how they are involved in flowering. I understand the basics about Pfr and Pr but I don't understand how they can cause flowering... does the accumulation of one of the type of phytochromes cause chemical changes which causes budding to take place etc?
Original post by FutureMedic97
Hey everyone,
Could someone please explain phytochromes -as in how they are involved in flowering. I understand the basics about Pfr and Pr but I don't understand how they can cause flowering... does the accumulation of one of the type of phytochromes cause chemical changes which causes budding to take place etc?


pR( sunlight/ red-light)----> pFR
pFR (far-red light/ darkness)----> pR

pFR only affects flowering
Flowering is due to night length
e.g. Short-day plants only flower when night-length is greater than day length, long-day plants only flower when night length is shorter than day length

pFR inhibits SD flowering and promotes LD flowering

Long-day plants:
Long-day plants use PFR to trigger the flowering process.In mid-summer, nights are too short to convert all of the PFR into PR. This results in many PFR proteins becoming bound to receptor proteins, which in turn ‘turn on’ genes that produce flowers.

Short-day plants:s-smilie:hort-day plants use PFR to inhibit the flowering process.Thus, near mid-summer, the protein receptors of short-day plants act to ‘turn off’ the flower-producing genes. By autumn, day-length is short so PFR levels drop too low to inhibit flowering, thus flowering begins.

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