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    (Original post by tofaeal)
    Can someone explain resting potential and action potential
    resting potential is when the axon is stable and has no action potential being sent down it. in most cases the resting potential is around -70. this means that the inside of the axon is more negative than the outside due to the sodium potassium pump.
    This pump works by removing 3 Na+ ions out for every 2K+ into the axon. therefore you can see that the inside in relation to the outside of the axon is negative as there are less ions inside.
    an action potential happens when a threshold value has been triggered. so for instance if you put pressure on your finger the gel-mediates sodium stretch channels will move. as a result the Na+ channels open causing an influx of sodium ions and thus removing K+ ions out of the axon. now the opposite has happened to when first explaining the resting potential. the inside has depolarised and thus become more positive therefore creating an action potential. this potential moves across the whole length of the axon is unmyelinated axons, or will jump by saltatory conduction in a myelinated axon.
    i hope this makes sense, im not the best at explaining.
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    (Original post by Ameera226)
    Does anybody know if we need to know the differences in protein synthesis between prokaryotes and eukaryotes?
    nope, just remember from AS that prokaryotes DNA is not involved with proteins due to them not having chromosomes.
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    (Original post by tofaeal)
    Can someone explain resting potential and action potential
    Resting potential is the potential at which the neurone is at rest, -70mV (no action potential)
    Carrier proteins actively transport 3Na+ ions out of the axon and 2K+ ions in; channel proteins also cause unequal diffusion of K+ ions out than Na+ in. These contribute to a negative charge inside the axon (-70mV) relative to the outside.

    Action potential is the rapid reversal of charge inside the axon. Happens by:
    1) Depolarisation generator potential from a receptor (caused by stimuli) opens voltage gated sodium ion channels causing rapid diffusion of Na+ (increasing charge).
    2) Repolarisation - Na+ ion channels close and K+ channels open so K+ diffuse out (reducing charge)
    3) Hyperpolarisation - K+ stay open while Na+ is actively transported out, causes an 'undershoot'. K+ eventually closes and resting potential is restored.

    Something like that. Someone correct me if I'm wrons because that was out of my memory.
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    Can someone explain the refractory period please? Whats its purpose and why does the K+ overshoot?
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    What's the difference between in vitro and in vivo? So confused :s Is In-vitro specifically for making DNA fragments (reverse transcriptase, Restriction endonucleases and PCR) while Vivo is for genetic recombination and cloning of bacteria (vectors)?
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    (Original post by Ozy96)
    Can someone explain the refractory period please? Whats its purpose and why does the K+ overshoot?
    There are 2 "definitions" for ref. period
    -Absolute ref. period : short period of time when an Action pot. CANNOT be initiated
    -Relative ref. period : when the generator potential must reach a higher threshold limit to initiate an action pot.

    Undershoot is because of hyperpolarisation when K+ ion channels remain open while Na+ is actively being transported out so ?higher rate of positive ion transport out?
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    Can someone explain the generator potential, how it's formed and how it leads to an action potential?
    Thanks
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    (Original post by shiney101)
    Can someone explain the generator potential, how it's formed and how it leads to an action potential?
    Thanks

    A generator potential is a change in the potential difference of a receptor cell due to a stimulus, which has caused the cell membrane to become more permeable to ions. When a generator potential reaches the threshold level it will result in an action potential within a neurone. The stimulus which causes the action potential causes the neurone membrane to change shape, so sodium channels will open. Some of the sodium ions that have entered the neurone diffuse to the side and cause sodium voltage-gated channels in the next region of the neurone to open and cause a further influx of ions - the movement of depolarisation is the action potential. .
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    The energy from a stimulus creates a generator potential by Na+ ions diffusing into the membrane of the axon. Na+ ions causes the membrane to become depolarised (less negative). If the generator potential exceeds a certain threshold, an action potential is created. This is continued along the axon as adjacent voltage gated sodium ion channels open and depolarise the membrane further and further along the axon.
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    (Original post by Shiroe)
    What's the difference between in vitro and in vivo? So confused :s Is In-vitro specifically for making DNA fragments (reverse transcriptase, Restriction endonucleases and PCR) while Vivo is for genetic recombination and cloning of bacteria (vectors)?
    Both types of cloning involve the formation of a required gene - so making DNA fragments.

    In vitro takes place outside a living organism - so PCR to form the gene. PCR can also be used to create probes or replicate DNA strands for processes such as genetic fingerprinting when the sample is small (such as during forensic investigations).

    In vivo takes place within a living organism, so when the organism grows and replicates its DNA it creates copies of the gene - the insertion of a gene into a plasmid.

    The use of restriction endonuclease and reverse transcriptase are methods to isolate the required gene from the DNA strand. Reverse transcriptase translates mRNA for a gene back into DNA (complementary DNA or cDNA), where as restriction endonuclease cuts the gene from DNA at a recognition site - following a 6 base pair palindromic sequence - which allows the formation of 'sticky ends'. If the plasmid is cut with the same restriction endonuclease, the ends of the cut gene and plasmid will be complementary and so they can join together through DNA ligase. So these enzymes can be used for in vivo cloning.
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    Does anyone have any 25 mark predictions from a reliable source ? I'm desperate
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    just commenting so i know where i have got up to
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    (Original post by Malicious)
    Does anyone have any 25 mark predictions from a reliable source ? I'm desperate
    My teacher said they can literally ask ANYTHING. So my best suggestion is that you try to learn all the basics from the other units wihtout too much detail and just go for breadth (quantity) marks instead of depth (quality). Because thats what I'm doing.
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    Hi does anyone have any notes for Biol5 havent made a single one or been able to learn anything due to being in and out of the hospital throughout the year it'd be very much appreciated if someone could PM the synoptic essays aswell x
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    (Original post by member1234)
    Hi does anyone have any notes for Biol5 havent made a single one or been able to learn anything due to being in and out of the hospital throughout the year it'd be very much appreciated if someone could PM the synoptic essays aswell x
    Hope you're feeling well now.

    Try these notes that I've attached to this post, you may find them helpful.

    As for the synoptic essay I've also attached key points from each unit.
    Attached Images
  1. File Type: pdf AQA A2 Biology Unit 5 Revision Notes.pdf (154.3 KB, 338 views)
  2. Attached Files
  3. File Type: docx Essay List.docx (32.9 KB, 462 views)
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    Does anyone else feel very unprepared? I havent done any past papers yet so i am very worried still need to go through all the content aswell, managed to do half today
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    Any predictions on what the essay options are going to be?
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    How can you revise the assay ? I have done a few but not all the topics from AS.
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    Can someone please help me with genetic fingerprinting?!

    thank you
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    (Original post by michsitiy)
    How can you revise the assay ? I have done a few but not all the topics from AS.
    I've been writing out plans for possible essay questions and what I would include from each unit so I know what to revise. I've also been revising the topics that come up often. I don't know if this helps?
 
 
 
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