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

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    (Original post by percy93)
    need help, can someone explain the refractory period for me? i'll rep your ass?
    The refractory period is the period after the transmission of the action potential in which no action potentials due to sodium voltage-gated channels being closed. This means that action potentials are kept separate from another, are discrete and the number of them is limited.
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    What do we need to know about chemical messengers such as histamines?
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    (Original post by flowerscat)
    - because larger fragments are harder to sequence, and lead to more errors

    what restriction endonucleases
    - trial and error - you want it cut to reasonably-sized chunks, but not into really small fragments or they will be hard to put back together. Think of it like a jigsaw, the smaller the pieces the harder it is to figure out how they go back together.
    thanks! So basically, restriction endonucleases are specific when you're trying to extract a gene to use in vectors.
    Otherwise, restriction endonucleases are random to make the DNA into fragments which is easier to process and reduces chance of mistake.

    Is that correct? x
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    (Original post by percy93)
    need help, can someone explain the refractory period for me? i'll rep your ass?
    Refractory period is to produce discrete impulses which are unidirectional. Occurs because potassium ions channels are slow to close to there is a slight 'overshoot' when too many potassium ions diffuse out the neurone, and sodium channels cannot open.
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    (Original post by angel1992)
    why does fsh need to be lowered by negative feedback in the first section of the oestrous cycle?
    I think its so more than one follicle doesn't grow
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    Hey dudes does anyone know any good websites with biology essays so i can compare?
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    (Original post by KingMessi)
    No, they don't-are they ever hormones? Dopamine, and serotonin aren't? :confused:

    Restriction mapping is meant to give you the sequence of the DNA fragments; basically the genome is usually too big to sequence in one go, so you use restriction endonucleases to to cut the genome; but, after sequencing these separate fragments, you need to put the genome back together; by using pairs of restriction endonucleases and looking at where they cut, one can determine the sequence of genes....
    I was thinking of histamine which is a hormone isn't it? and can be a neurotransmitter.
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    (Original post by Abby :))
    Can someone explain the whole antibitiotic resistance thing in identifying if Vectors have been taken up. o.O

    I really really dont understand how the textbook explains it.
    All i know is there is something involving tetracycling and acetyl or something
    And if the vector is still apparent then it has taken the vector up?

    -.- Hehe
    Okay... the plasmid starts out with two different genes that have resistance to two different antibiotics. lets call these antibiotic resistance genes A and B just because I don't know any names of antibiotics off hand.

    One of the genes has to be cut into using the restriction endonuclease and the new dna is inserted. In that plasmid, it now only has B not A. Some plasmids close before taking the dna so they have A and B. When they get put into the bacteria, some get one with just B, some get one with A and B and some don't take one up at all.

    If you expose the bacteria all to the antibiotic B, all the bacteria that didn't take up any plasmid will die and you will be left with the ones you want and those that took up unchanged plasmids. Then a process called replica plating takes place where bacteria of both kinds are spread out onto two plates in the same plate and one plate is given antibiotic A. Those that die did take up the wanted plasmid with your DNA so then these on the second plate can be replicated.

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    For in vivo cloning, when can the marker gene be inserted into the vector?
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    (Original post by percy93)
    need help, can someone explain the refractory period for me? i'll rep your ass?
    basically the refractory period occurs after an action potential has been created and the sodium ion channels are closed (therefore further action potential cant be created as an influx of sodium ions cant occur)
    during the refractory period the membrane is hyperpolarised as potassium ions diffuse out of the membrane, causing is to be 'more negative' than it normally would (-65mv)
    the refractory period therefore ensures only discrete impulses are produced as an action potnetial cannot form immediately after the other. it also ensure that the nerve impulse is unidirectional as the action potential will not be able to travel backwards

    BAM
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    (Original post by Munster)
    Hey dudes does anyone know any good websites with biology essays so i can compare?
    ANYONE?
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    (Original post by stressedatschool)
    I was thinking of histamine which is a hormone isn't it? and can be a neurotransmitter.
    No, histamine is a chemical mediator, NOT a hormone-I'm sure of it.
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    (Original post by xelaman)
    Has anybody thought about what extra content they will include-outside of the syllabus for the essay?
    Random stuff I have seen on TV most likely in very what seemed pointless at the time but are now life saving documentories
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    (Original post by Aiboz)
    For in vivo cloning, when can the marker gene be inserted into the vector?
    When the genome of the organism and the plasmid have been cut with the same restriction endonuclease.
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    OMG this thread has just reiterated how little i know...

    What are you all revising for the 25 mark? Any predictions for what it could be ?
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    Can someone summarise restriction mapping for me in a simple way? I understand all the other tech stuff but I'm struggling with that one.
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    i reckon control of body temperature and homeostasis will be a major question this year seeing as it didnt come up last year. and the whole endothermy and ecothermy stuff ksjdhfkehfek
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    the genetic stuff really confuses me
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    (Original post by diskohuelga)
    Can someone summarise restriction mapping for me in a simple way? I understand all the other tech stuff but I'm struggling with that one.
    http://www.thestudentroom.co.uk/show...369&highlight=

    Er, hopefully simply enough?
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    Anyone fancies to do a recap of chapter 16? For me is the hardest one :/
 
 
 
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