Turn on thread page Beta

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

  • View Poll Results: Are you resitting this unit?
    YES!
    12.91%
    NO!
    87.09%

    • Thread Starter
    Offline

    13
    ReputationRep:
    Animation on diabetes and more.

    http://highered.mcgraw-hill.com/site...diabetics.html
    Offline

    0
    ReputationRep:
    On chapter 15 question 4 it is concerned with cancer and so the cell cycle which involves the replication of DNA. Yet on the mark scheme it talks about protein synthesis... Is that just the mark scheme being wrong or me being incredibly blind and not realising the right answer?
    Offline

    0
    ReputationRep:
    Gene sequencing!
    Offline

    0
    ReputationRep:
    (Original post by sleungs)
    So if you were asked to define a "stem cell" or a "totipotent cell" what would you say?

    Just read the Wiki article and it seems to me that a zygote is a totipotent cell. There are no other cells which are totipotent. When it divides and develops into an embryo, the cells are then called stem cells? Basically I have no idea what I'm talking about!
    well a stem cell is still able to differentiate. A totipotent cell can specialise into ANY cell. Multipotent- can only specialise into a few cells.
    Offline

    0
    ReputationRep:
    Why are mark schemes so infuriating?
    Last year for the 3 mark question: "During an action potential the membrane potential rises to +40mV and then falls. Use information from the graph to explain the fall in membrane potential".

    The mark scheme said:
    Potassium channels open;
    Potassium out;
    Sodium channels close

    It just seems so simple
    Offline

    0
    ReputationRep:
    (Original post by Ineluctable)
    Why are mark schemes so infuriating?
    Last year for the 3 mark question: "During an action potential the membrane potential rises to +40mV and then falls. Use information from the graph to explain the fall in membrane potential".

    The mark scheme said:
    Potassium channels open;
    Potassium out;
    Sodium channels close

    It just seems so simple

    That's an exception normally they want you to write every word they want to gain full marks in those 3 markers.
    Offline

    0
    ReputationRep:
    (Original post by Destroyviruses)
    I do indeed I made a table.

    All gene and genetic engineering papers (more so of the older ones)
    All energy ,control ... papers ( more so of the older)

    Jun 07 of Behaviour

    And June 06 and 07 of Microbes.

    Thankyouu
    Offline

    2
    ReputationRep:
    (Original post by JB13)
    Can anyone in really, really simple turns please explain gene sequencing? I've tried most textbooks and things and just cannot understand it! Thanks
    OK, I will try :-)

    You need four tubes. In each tube add equal amounts of DNA to the sequenced, polymerase, radioactively-labelled primers, free nucleotides (A,T,G,C) and water.

    You have four terminator bases - I will represent them as ddA, ddT, ddG and ddC. Terminator bases can only form a bond on one side and not the other. So if a terminator base gets incorporated into DNA, it will no longer grow, as polymerase cannot link it to the next base.

    Add one of the terminators to each of the four tubes. Run the reaction. Primers will attach to DNA and polymerase will start synthesising the complementary strand.

    The chance of incorporating a "normal" base or a "terminator" base is equal. Thus each time a new base gets incorporated, either of these bases will H-bond to the original DNA strand. If a "normal" base is incorporated, then polymerase continues to attach the bases together. If a terminator base is incorporated, then synthesis of the complementary strand stops at that point.

    Thus in each tube you end up with a mixture of fragments, terminated at different lengths. (you need to draw this out for yourself to understand it better).

    Each of these four tubes is run next to each other on the gel, where they separate according to size. You then detect the bands using an X-ray film (since the primers are radiolabelled).

    As only the primers are radio-labelled, you only detect the fragments of the complementary strand, never the original DNA.

    You read the sequence of the complementary strand, starting from the lowest band in the gel (which corresponds to length of one primer + one base). You read the bases from the bottom to the top of the gel, in order of size.

    Translate this into its complementary base. This will be the sequence of the DNA that you were trying to find out.
    Offline

    0
    ReputationRep:
    Please can someone explain restriction mapping to me?
    Offline

    1
    ReputationRep:
    (Original post by Sparkly-Star)
    What last minute revision are you guys doing? I'm revising chapters and gonna do the tons of past papers we have... might do synoptic revision if I have time...
    I just read through my book and highlight key phrases. I did questions yestrday which i may read over if i have time.
    Offline

    0
    ReputationRep:
    (Original post by flowerscat)
    OK, I will try :-)

    You need four tubes. In each tube add equal amounts of DNA to the sequenced, polymerase, radioactively-labelled primers, free nucleotides (A,T,G,C) and water.

    You have four terminator bases - I will represent them as ddA, ddT, ddG and ddC. Terminator bases can only form a bond on one side and not the other. So if a terminator base gets incorporated into DNA, it will no longer grow, as polymerase cannot link it to the next base.

    Add one of the terminators to each of the four tubes. Run the reaction. Primers will attach to DNA and polymerase will start synthesising the complementary strand.

    The chance of incorporating a "normal" base or a "terminator" base is equal. Thus each time a new base gets incorporated, either of these bases will H-bond to the original DNA strand. If a "normal" base is incorporated, then polymerase continues to attach the bases together. If a terminator base is incorporated, then synthesis of the complementary strand stops at that point.

    Thus in each tube you end up with a mixture of fragments, terminated at different lengths. (you need to draw this out for yourself to understand it better).

    Each of these four tubes is run next to each other on the gel, where they separate according to size. You then detect the bands using an X-ray film (since the primers are radiolabelled).

    As only the primers are radio-labelled, you only detect the fragments of the complementary strand, never the original DNA.

    You read the sequence of the complementary strand, starting from the lowest band in the gel (which corresponds to length of one primer + one base). You read the bases from the bottom to the top of the gel, in order of size.

    Translate this into its complementary base. This will be the sequence of the DNA that you were trying to find out.
    Thank you! That seems to make a bit more sense. I'll try and draw it out now. Thanks for spending the time to explain it though
    Offline

    11
    ReputationRep:
    (Original post by JB13)
    Can anyone in really, really simple turns please explain gene sequencing? I've tried most textbooks and things and just cannot understand it! Thanks
    You get a mixture of the following:
    1) A single stranded piece of DNA
    2) DNA polymerase
    3) DNA primer
    4) Free nucleotides
    5) Florescently labeled modified nucleotides.

    OK, so you do what you do with PCR. Heat it to 95C to break H-bonds, cool to 50-65C to allow primers to bond, heat to 72C to allow DNA polymerase to work.

    The difference is that the modified nucleotides are chain-terminating nucleotides (that's why it's called the chain termination method). They lack a third OH group which prevents the phosphodiester bond between two nucleotides. This means that once one of these modified nucleoides binds, no more can bind. Therefore, you're going to get different lengths of DNA fragments. The later the modified nucleotide binds, the longer the fragment.

    So when you use electrophoresis to separate out the strands based on mass, the smaller ones will travel the furthest. The smallest fragment will only have one normal base and one modified. So the modified shows up in UV light (because florescently labeled) and you can determine what base is complementary to the modified one.

    From here you read the bands from the bottom of the gel up. Building up the whole sequence of the DNA one at a time E.G. the first band has modified 'T*' so the first base pair must be 'A-T', the second band is modified 'C*' so the second base pair must be 'C-G'. Go along the whole DNA using this method.

    Sorry for the long post!

    EDIT: BEAT ME TO IT!
    Offline

    0
    ReputationRep:
    (Original post by IFondledAGibbon)

    Sorry for the long post!

    EDIT: BEAT ME TO IT!
    So in the NT book page 268 (last paragraph) the DNA strand would be AT, GC, CG and so on?
    Offline

    0
    ReputationRep:
    (Original post by IFondledAGibbon)
    You get a mixture of the following:
    1) A single stranded piece of DNA
    2) DNA polymerase
    3) DNA primer
    4) Free nucleotides
    5) Florescently labeled modified nucleotides.

    OK, so you do what you do with PCR. Heat it to 95C to break H-bonds, cool to 50-65C to allow primers to bond, heat to 72C to allow DNA polymerase to work.

    The difference is that the modified nucleotides are chain-terminating nucleotides (that's why it's called the chain termination method). They lack a third OH group which prevents the phosphodiester bond between two nucleotides. This means that once one of these modified nucleoides binds, no more can bind. Therefore, you're going to get different lengths of DNA fragments. The later the modified nucleotide binds, the longer the fragment.

    So when you use electrophoresis to separate out the strands based on mass, the smaller ones will travel the furthest. The smallest fragment will only have one normal base and one modified. So the modified shows up in UV light (because florescently labeled) and you can determine what base is complementary to the modified one.

    From here you read the bands from the bottom of the gel up. Building up the whole sequence of the DNA one at a time E.G. the first band has modified 'T*' so the first base pair must be 'A-T', the second band is modified 'C*' so the second base pair must be 'C-G'. Go along the whole DNA using this method.

    Sorry for the long post!

    EDIT: BEAT ME TO IT!
    Ahh I really am starting to get this! Thank you very much as well much appreciated! Good luck tomorrow
    Offline

    0
    ReputationRep:
    Restriction Mapping explanation please?
    Offline

    2
    ReputationRep:
    (Original post by booooom)
    for an essay question on the importance of negative and positive feedback, what can be included from unit 1, 2 and 4?
    Unit 1, - when helper T cells produce cytokines, these cytokines stimulate more production of T cells.
    - lungs, The respiratory centre transmits regular nerve impulses to the diaphragm and intercostal muscles to cause inhalation. Stretch receptors in the alveoli and bronchioles detect inhalation and send inhibitory signals to the respiratory centre to cause exhalation. This negative feedback system in continuous and prevents damage to the lungs.

    unit 2- heamoglobin - low oxygen increase epo hence red blood cells negative feedback

    Unit 4- respiration, too much respiration-less oxygen,less respiration occurs

    just throwing ideas around here.
    Offline

    0
    ReputationRep:
    I am seriously ****ting myself for this exam, there's so much to learn, I didn't realise how big the module was until just now. Waaah!!! :-(
    Offline

    2
    ReputationRep:
    (Original post by Tericon)
    Restriction Mapping explanation please?
    Originally Posted by flowerscat
    OK, I will try :-)

    You need four tubes. In each tube add equal amounts of DNA to the sequenced, polymerase, radioactively-labelled primers, free nucleotides (A,T,G,C) and water.

    You have four terminator bases - I will represent them as ddA, ddT, ddG and ddC. Terminator bases can only form a bond on one side and not the other. So if a terminator base gets incorporated into DNA, it will no longer grow, as polymerase cannot link it to the next base.

    Add one of the terminators to each of the four tubes. Run the reaction. Primers will attach to DNA and polymerase will start synthesising the complementary strand.

    The chance of incorporating a "normal" base or a "terminator" base is equal. Thus each time a new base gets incorporated, either of these bases will H-bond to the original DNA strand. If a "normal" base is incorporated, then polymerase continues to attach the bases together. If a terminator base is incorporated, then synthesis of the complementary strand stops at that point.

    Thus in each tube you end up with a mixture of fragments, terminated at different lengths. (you need to draw this out for yourself to understand it better).

    Each of these four tubes is run next to each other on the gel, where they separate according to size. You then detect the bands using an X-ray film (since the primers are radiolabelled).

    As only the primers are radio-labelled, you only detect the fragments of the complementary strand, never the original DNA.

    You read the sequence of the complementary strand, starting from the lowest band in the gel (which corresponds to length of one primer + one base). You read the bases from the bottom to the top of the gel, in order of size.

    Translate this into its complementary base. This will be the sequence of the DNA that you were trying to find out.
    just scroll up!
    Offline

    0
    ReputationRep:
    (Original post by Destroyviruses)
    just scroll up!
    That's DNA Sequencing
    • Thread Starter
    Offline

    13
    ReputationRep:
    Great I just realized I had to learn the specifics of the adrenaline and glucagon second messenger model. :cry2: I hope I don't forget it!
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: June 22, 2016

University open days

  1. University of Cambridge
    Christ's College Undergraduate
    Wed, 26 Sep '18
  2. Norwich University of the Arts
    Undergraduate Open Days Undergraduate
    Fri, 28 Sep '18
  3. Edge Hill University
    Faculty of Health and Social Care Undergraduate
    Sat, 29 Sep '18
Poll
Which accompaniment is best?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.