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AQA BIOL5 Biology Unit 5 Exam - 22nd June 2011 watch

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    in the NT book it also states that gene therapy can involve gene replacement, but how do they replace the gene, it shows how they supplement it, but replace it??
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    (Original post by Destroyviruses)
    However if the DNA strand is too long the chance of error can get so high the it renders the copied DNA invalid?
    Haven't seen anything about the error being an issue. If it was then surely in DNA replication , where a full strand is copied, the chance would be highest and yet that is still valid?
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    (Original post by angel1992)
    im confused, how is that recombinant dna? and how is that used ? ohhhh are you saying that dna is isolated by reverse transcriptase and so dna using this is recombiant which is then used in pcr and genetic fingerprinting?
    Yup!
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    (Original post by ZacVR)
    Haven't seen anything about the error being an issue. If it was then surely in DNA replication , where a full strand is copied, the chance would be highest and yet that is still valid?
    I was just guessing, trying to find a reason why the book says only small strands can be used in PCR.

    Maybe it got confused with sequencing.
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    (Original post by emmaaa65)
    woahhh everyone on here is in proper panic mode!
    although saying that i am too hahaha
    im not even going to attmept to try and understand positive and negative feedback properly lol
    Positive feedback is like art school.

    Negative feeback is like a private school.
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    in gene therapy, when adenoviruses are used is the plasmis inserted into the adenovirus's dna and how?
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    (Original post by mbr)
    I don't get any of that recombinant DNA stuff ! Please help
    The recombinant DNA. Is just DNA that is made using mRNA.

    For example if you know an mRNA codes for a particular protien and you want loads of that protein. You can get a bacteria to make it for you. But you'll need it in DNA form so it can be inserted into plasmids.

    To turn the mRNA into recombinant DNA. You use a particular enzyme called reverse transcriptase (see its a nice name because its the oposite of transcription so REVERSE TRANSCRIPTASe)

    So recombinant DNA is nice when you want only a particular gene.Because they are made from mRNA and mRNA obly code for particular genes.
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    (Original post by Destroyviruses)
    Positive feedback is like art school.

    Negative feeback is like a private school.
    What :lolwut:
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    hey guys
    in the june 10 paper, in q6)c)ii) why can you not write about 'oncogenes' to get the mark?
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    can someone please outline for me the mentrual cycle and what we need to know
    thank you
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    ARGH!!! i hate biology!!

    they should ban the stupid essay. how do they expect u to remeber everything from the past four units in detail.
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    (Original post by tehsponge)
    What :lolwut:
    Lol !

    Private schools try to make you conform and be normal

    Art schools encourge you do deviate from the norm!
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    (Original post by Destroyviruses)
    Lol !

    Private schools try to make you conform and be normal

    Art schools encourge you do deviate from the norm!
    Ah I see
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    (Original post by leesh18)
    can someone please outline for me the mentrual cycle and what we need to know
    thank you
    Dont thank me that this other dude in the thread that posted this, I just copied it to safe
    Attached Files
  1. File Type: docx oestrous cycle.docx (10.6 KB, 166 views)
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    i dont know if this has been posted on pervious threads but have any teachers given hints on what topics might come up for the essay???
    please quote me when replying,
    thank you.
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    Eeek!! Exam in 2 days and I'm really worried about the synoptic essay!! Can anyone help me make a list of topics to revise? So far, I think:
    Biol1:
    Enzymes
    Carbohydrates
    Cell surface membranes
    Diffusion, Osmosis, active transport
    cardiac cycle
    respiratory cycle

    Biol2:
    Meiosis+mitosis
    gas exchange

    Biol4:
    respiration
    photosynthesis
    cycles

    Biol5:
    muscle contraction
    protein synthesis
    homeostasis
    in vivo, in vitro?

    Anything else?
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    (Original post by victordudes)
    Eeek!! Exam in 2 days and I'm really worried about the synoptic essay!! Can anyone help me make a list of topics to revise? So far, I think:
    Biol1:
    Enzymes
    Carbohydrates
    Cell surface membranes
    Diffusion, Osmosis, active transport
    cardiac cycle
    respiratory cycle

    Biol2:
    Meiosis+mitosis
    gas exchange

    Biol4:
    respiration
    photosynthesis
    cycles

    Biol5:
    muscle contraction
    protein synthesis
    homeostasis
    in vivo, in vitro?

    Anything else?
    http://store.aqa.org.uk/qual/gce/pdf/AQA-2410-W-SP.PDF

    Start reading from page 6

    Why do I have neg for this, the spec is very helpful. It makes you feel like youve covered everything. And it isnt long at all.
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    Why do they reject answers referring to oncogenes in that question on the 2010 paper? The examiners report doesn't help either, it says:
    Many candidates found part
    (ii) challenging and, although they were able to gain credit for a general statement
    relating to the uncontrolled division of cancer cells, they attributed this to insertion of the
    gene in the base sequence of either the tumour suppressor gene or into a protooncogene, thereby converting it into an oncogene.
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    (Original post by denisewoosey)
    me too i'm really confused about probes and restriction mapping :-)
    Probes: first of all, the definition for probes that seems to come across most often is short, single strands of DNA that have a base sequence complementary to the base sequence of part of the target gene. The probe can then bind to (or hybridise with) the target gene. Probes are labelled, usually radioactively (so to see where the probes have attached, it's exposed onto x-ray or photographic film) or with a fluorescent label (so the target gene will fluoresce under UV light). In a practical sense, this is used with restriction endonucleases to break the DNA sample into fragments, and then transferred to a nylon membrane (southern blotting) and incubated with the probe. If the gene is present, it will be labelled and can be detected. (To carry on this idea, if a disease causing gene/gene mutation has been identified, the best course of treatment can be decided.)

    On a large scale, probes are used for genetic screening for mutated genes as a part of a DNA microarray, where DNA is washed over an array of different DNA probes (for different mutated genes) and if the DNA binds to a specific probe, the mutation can be identified. [Note: in the specification, you're supposed to understand that scientific methods are constantly updated. This is an example, as DNA microarrays are much faster and cost-effective than using DNA probes on a smaller scale.] This again lets you consider treatments, and you can also bring up genetic counselling (e.g. whether or not to screen embryos if parents are a carrier for a mutated gene).

    Restriction mapping, meanwhile, is kind of horrible. First of all, restriction mapping is used for putting DNA fragments back in the right order, because in order for DNA sequencing to take place, the (labelled, this is important) DNA sample must first be cut into fragments using restriction endonucleases, and then separate the fragments by length using electrophoresis.

    You then get a nice little (haha, no) diagram:



    This is a pretty simplified version; it's possible you can get one with more than one restriction enzyme, but for let's keep it simple for now. Your total digest fragments are ones that have been completely cut by the enzyme (which I'm going to call enzyme A). Your partial digest fragments occur when the enzymes haven't been left long enough, so you can also get fragments of different lengths (in this instance, there isn't a cut after the 3kb fragment, so you have a fragment of 8kb because 3+5=8 - and in the mark schemes, they do apparently like to see you can add 3+5). The radioactive fragment is important, as this gives you your starting point - this is because the radioactive fragment is the one with the probe attached - so in this instance, because we have a partial fragment of 8 and not 7 (and so not 2+5), there are two recognition sequences and so the recognition map is...



    (Concise posts - this is how not to do it. )
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    Is anyone else just not bothering to prepare for the synoptic essay?

    I'm just going to have a blind stab at it when i finish the other questions
 
 
 
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