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    (Original post by iwantopas19)
    ok can someone explain what is post transcriptional changes?

    and do we need to know southern blotting? I dont see that in specification, but my teacher suggested me to learn it.?
    I dont think we need to know much about southern blotting but basically you once you have made a profile using gel electrophresis you get a pivce of parchemnt (i think) and then tranfer it onto that so you can see it more cleraly..correct me if i am wrong

    for transcriptional change
    basically once you have made the MRNA strand via transcrption you have parts of the DNA that dont code for amino acids. These are called intorns and the ones that do code are called exons. The Introns are removed via splicing and the exons are joined together in the nucleus. The exons can be joined together in different ways which means that there is more than one amino acid sequence thus it can code for more than one protien
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    (Original post by iwantopas19)
    glucose is fuel? can uplease explain?
    GLUCOSE is a fuel in respiration!!!

    It's brokken down into various other things and gives ATP!!! so it gives energy (i.e. it's a fuel)!
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    anyone have tips for answering all questions in time? i am struggling with past papers, the best I managed was finishing 7 questions in time :facepalm: guys share your speed tips please!
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    (Original post by iwantopas19)
    ok can someone explain what is post transcriptional changes?

    and do we need to know southern blotting? I dont see that in specification, but my teacher suggested me to learn it.?
    • Genes have exons (coding regions) and introns (non-coding regions)
    • the whole gene is trancribed into mRNA
    • Introns are then cut out, leaving just the exons sections
    • Exons are spliced together to make functional mRNA.
    • The exons can be arranged in different ways so that several types of mRNA are produced, which will then be translated into several diff. proteins
    • This is called post-transcriptional processing where one gene forms several different types of proteins


    Hope this helps
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    Does anyone have any advice for last minute revising..have done all the past papers twice should i just go through the syllabus?
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    (Original post by Sravya)
    okay in terms of the graph questions:
    I always say what happens generally? Like does one factor increase because of another..thus what sort of correlation it is. I look for any anomolies.. i look for any patterns. I always try and briefly suggest what the graph is trying to say, So like if one factor is increasing because of temperature I always say that is because of an increase in kinetic energy and therefore an increase number of collisions. I always do a manipulation. This could be the overall change in the graph. So the change/ original * 100. It also depends what the question is saying like you may be describing an irrelevant part of the graph

    For photosynthesis ill try and write down what i always try and include in these questions:
    for the light dependant reaction, takes place in the thylakoid membranes of the chloroplasts.and needs light Basically what happens is light is absorbed by phtosystem 2(PSII) and then this splits water into hydrogen and oxygen via photolosis. Oxygen is a waste product. The electrons are excited and their energy level is increased. They are released from PSII and go onto the electron transport chain via the electron carries (this next bit ive never seen come up in a mark scheme but id put it in anyway- There is a higehr concentration of protons in the thylakoid so you get a proton concentration gradient. The protons move down the concentration gradiet via the enzyme ATP synthase which allowes the combination of ADP plus P to get ATP. You also will get NADPH. This is when light is absorbed by PSI and the electrons are transfered with a H proton from the stroma to the NADP to get NADPH.

    So essentially when you write an answer on the light dependant reaction make sure you include
    -light absorbed by PSII
    - light splits water into H+ and o2
    -Electrobs ebergy raised because of excitment
    - Electrons are released to ETC
    -redox reactions occour to synthesize ATP from ADP and P. Whilst this is happening energy of electrons fall
    -called phosphorylation
    -NADPh is formed when one H+ is added to NADP from the stroma

    for light independant reaction
    a classic markscheme would want you to contain the folowing

    - happens in the stroma
    -doesnt need light
    -it is the calvin cycle or known as carbon fixing
    -cCO2 enters via the stomata of leaf
    -combines with the 5 carbon RUBP
    -with the help of the enzyme RUBISCO
    -Creats an unstable 6 carbon compound which splits into 2, 3 carbon compounds called GP
    - Redection reaction occours where by using the energy from ATP it takes the hydrogen from NADPH and adds it to GP to get GALP
    - 5/6 molecules of galp used to regenerate RUBP for the reaction
    - one is used to make amino acids, carboyhydrates, bucleic acids and lipids

    for the suggest why questions:
    These involve you to think...sometimes the answer is really obvious so always put down the obvious thing. There is no way of giving advice for these questions excpet think about what you are going to write and it will always link to the syllabus

    for the immune response questions
    There is lots they could ask you on
    Fristly the different types
    The fitrst defence a body has s the kertin on the skin forms a physical barrier that protect pathogens form entering
    -Skin flora on the skin comepete wiht bacteria to stop them from breeding there
    - lysosomes n teras kill bacteria by weaking their cell walls so when they divide they burst and die.
    - In the stomach you have hydrcholic acid whihc does not allow bacteria to survive you can only have specially adapted bacteris in the stomach
    you have the non specific...
    there are 4 types
    Inflamation

    Theis is when the immune system recognises anitgens and the release histamine
    - this causes vasodilation
    -this increases the blood flow
    -this means lots of immune cells like white blood cells will seep to the site of the infection and then the immune system can start to destroy the pathogen

    Lysozome action
    This si where lysozomes break down bacteria
    - they do this by weakening cell walls
    - they only affect bacteria not viruses as viruses dont have a cell wall

    Interfernons

    these are protiens which are anti viral
    -They prevent replication by inhibiting the production of viral proteins
    - They dont affect bacteria as bacteria dont make proteins in the same way that viruses do

    Phagocytosis

    So the phagocyte recognises the antigen on the pathogen
    -It engulfs the pathogen and contains it in a pphagocytic vaculoe
    A lysosome fuses with the vacuole and enzymes are released to break down the pathogen
    - The phagocyte presents this to the other immune cells like the T cell
    This can allso be known as the antigen cell presenting immune response

    Another type of immunity is the Specific immunity
    Firstly you need to know about antibodies
    - They are glycoprotiens. They have a 3D Y shape with disulphide bridges between the petides. They have a variable region which are specific to the antigens

    So what happens in the specific immune response is that something activates the T cell,. To activate the T cell it has to ve a complementary antigen. And a hagocyte could activate the T cell
    - once activated it differentiates into T helper cells-which go and activate the b cells
    - Or t killer cells whihc kill the pathogen
    - Or T memory cells which speeds up the immune response
    The T helper cell goes to activate the B cell
    The b cell again is specific and it has to be a complementary antigen
    Once the b cell is activated it divides into plasma cells. The plasma cells make antibodies whihc labes the antigen to allow phagocytes to phagocytose them. It can also bind to the toxins produced by the pathogens and prevent the toxins from affecting the humans

    That is the 2 types of immune responses

    If you are talking about types of immunity there are main ones

    Actuve immunity
    This can be natural where you become immune after catching the disease
    Or articificail where you become immune after reciveing a vaccine which contains a harmfull dose of the antigen...this could be an attenuated virus

    Passiv immunty
    this can be natural and this happens when a baby gets anitbodies from the mother through the placenta or breast milk
    It can be articifical if you are injected with a ton of antibodies

    Sorry its really long tried to include a lot..let me know if you need anything else its good revision for me too!
    and sorry about any spelling mistakes!
    thanks so much for taking time out to help! much appreciated, it all makes sense as well, im guessing its just a matter of properly learning everything for me.
    thanks again
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    (Original post by amber109)
    thanks so much for taking time out to help! much appreciated, it all makes sense as well, im guessing its just a matter of properly learning everything for me.
    thanks again
    No problem..do you have any other problem topics..id be more than happy to help...its really helping me
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    Describe how does the sequence of bases in a DNA molecule would be used to form the primary structure of a protein?
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    Hi guys just a last minute Q, hope u can help

    Basically there's a few questions which I get stuck on such as discuss the validity of such statements for graphs and how to interpret the graph to pick a valid statement etc... Does anyone have any advice on how to go about these Qs and how to interpret the graphs ?? Any help is appreciated
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    (Original post by bubblegummer)
    Describe how does the sequence of bases in a DNA molecule would be used to form the primary structure of a protein?
    1. idea of sequence of bases {forming the
    genetic code / determines the amino acid
    sequence} ;
    2. idea that one triplet codes for an amino
    acid;
    3. ref to (DNA) acting as a template ;
    4. reference to transcription OR detail of
    transcription e.g. DNA unzips, mRNA
    synthesis ;
    5. idea that mRNA moves from nucleus to
    cytoplasm / eq ;
    6. reference to translation OR detail of
    translation e.g. role of ribosome, codonanticodon
    interaction ;
    7. idea that tRNA carries an amino acid ;
    8. ref to formation of peptide bonds between
    amino acids ;
    9. idea that primary structure is the
    {sequence /order / eq} of amino acids ;
    10.comment on post-transcriptional
    modification of mRNA (between
    transcription and translation)e.g. removal
    of introns, splicing
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    (Original post by MBSSA)
    Hi guys just a last minute Q, hope u can help

    Basically there's a few questions which I get stuck on such as discuss the validity of such statements for graphs and how to interpret the graph to pick a valid statement etc... Does anyone have any advice on how to go about these Qs and how to interpret the graphs ?? Any help is appreciated

    In terms of validility usually the graph doesnt have enough data..also the graph never tells you about any other vairbales effecting it
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    Thanks!

    Posted from TSR Mobile
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    Difference between validity and reliability ?
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    (c) Suggest reasons for each of the following.
    (i) DNA polymerase from human sources is not suitable for use in a PCR
    machine.
    (ii) Species of plants cannot be identified from woody (xylem) material using PCR
    and DNA profiling.
    • Thread Starter
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    (Original post by amber109)
    (c) Suggest reasons for each of the following.
    (i) DNA polymerase from human sources is not suitable for use in a PCR
    machine.
    (ii) Species of plants cannot be identified from woody (xylem) material using PCR
    and DNA profiling.
    i) human sources can't take the extreme temperatures used in the PCR machine since the enzyme denatures
    ii) because xylem contains dead cells.
    • Thread Starter
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    (Original post by Helena Kennedy)
    Difference between validity and reliability ?
    I'm not too certain but validity is how recent the data is and reliability is what the source is and how many repeats etc were done, and when it was peer reviewed did other scientists find the same results etc.
    • Thread Starter
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    (Original post by Sravya)
    Does anyone have any advice for last minute revising..have done all the past papers twice should i just go through the syllabus?
    I would suggest reading through the textbook, and spec, and making a list of all the definitions you find (these are easy marks), and going through ALL the core practicals in depth. Also might be worth practising calculations involving trophic levels etc.
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    (Original post by amber109)
    (c) Suggest reasons for each of the following.
    (i) DNA polymerase from human sources is not suitable for use in a PCR
    machine.
    (ii) Species of plants cannot be identified from woody (xylem) material using PCR
    and DNA profiling.
    (i) DNA polymerase can only function at human temperature of 37 degrees, the temperature in PCR machine is too high and will denature the enzyme.

    (ii). xylem vessel is a dead cell and it does not have nucleus and thus no DNA is present so it cannot be detected
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    (Original post by Sravya)
    1. idea of sequence of bases {forming the
    genetic code / determines the amino acid
    sequence} ;
    2. idea that one triplet codes for an amino
    acid;
    3. ref to (DNA) acting as a template ;
    4. reference to transcription OR detail of
    transcription e.g. DNA unzips, mRNA
    synthesis ;
    5. idea that mRNA moves from nucleus to
    cytoplasm / eq ;
    6. reference to translation OR detail of
    translation e.g. role of ribosome, codonanticodon
    interaction ;
    7. idea that tRNA carries an amino acid ;
    8. ref to formation of peptide bonds between
    amino acids ;
    9. idea that primary structure is the
    {sequence /order / eq} of amino acids ;
    10.comment on post-transcriptional
    modification of mRNA (between
    transcription and translation)e.g. removal
    of introns, splicing

    thank you!! :3
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    Looking at the past few papers, me and my friend came up with what we think will come in the paper tomorrow as:
    -TB
    -Photosynthesis
    -Non-specific response
    -Possible Gel electrophoresis
    -Succession
    -Speciation
    -Abiotic and Biotic factors
 
 
 
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