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    Thought I'd add this on as thread about last exam seemed very popular. I'm guessing everyone has started with meiosis, lac operon etc. Link below has some good animations that have helped me. Will get some more helpful links up soon.

    http://www.sumanasinc.com/webcontent...s/biology.html
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    First vultures, then came the seals.... I think I've got it... I'm pretty sure that it's going to be a cow.

    On a side note - I randomly flicked past pg 111 from the Heinemann text book and something caught my eye.

    Spoiler:
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    Perhaps OCR was paying their respects to the seal. :dontknow:
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    [QUOTE=_lynx_]First vultures, then came the seals.... I think I've got it... I'm pretty sure that it's going to be a cow.


    hahahaaa
    seriously though genetics is hardcore stuff ,need to have many doses of caffine before i open the book
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    I've started my revision, even though we haven't even finished learning all the modules in class. Around 3 months to go, need to ace this exam!
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    Right, here is what I've learnt so far:

    Cellular control

    Gene - length of DNA which codes for a polypeptide, including enzymes. e.g. Hb, Keratin.

    Genetic code - A sequence of nucleotide bases in a gene which provide the code with the instructions for the construction of a polypeptide / protein.
    Characteristics: Triple code, degenerate code, widespread but not universal and some codes do not code for the AA, so this indicates 'Stop' (end of a polypeptide chain).


    Transcription:

    A sequence of nucleotides within a gene which are used in the construction of polypeptide.
    The creation of a single-stranded mRNA copy is needed as proteins are made in the cytoplasm (ribosomes) and NOT in the nucleus.
    Free RNA and DNA nucleotides
    4 activated RNA nucleotides : ATP, CTP, GTP, UTP.

    Process:

    1) Gene to be transcribed is unwinded and unzipped - H-bonds between the complementary nucleotide bases breaks.
    2) Free RNA nucleotides binds to the H-bonds with the exposed complementary nucleotide bases:

    T-A, A-U, G-C <<< catalysed by the enzymes - RNA polymerase.

    3) 2 extra phosphoryl groups are released, which releases energy to bond the adjacent nucleotides.
    4) mRNA is produced - it is complementary to the nucleotide base sequence on the DNA template strand (so similar to the DNA coding strand).
    5) mRNA is released - passes out of the nucleus >> nuclear pore >> nuclear envelope >> ribosomes.
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    Translation

    Polypeptides are assembled into AA in ribosomes.
    mRNA moves along ribosome and AA are assembled in the correct order.

    tRNA: - length of RNA
    - has 3 exposed bases at one end (binded to the AA)
    - has 3 unpaired bases at the other end (anti-codon)

    How the polypeptides are assembled:

    1) mRNA binds to the ribosome, so 2 codons are attached to the ribosome.
    First codon - tRNA forms H-bonds with the AA.

    2) Second tRNA binds with the second exposed codon (complementary).

    3) Peptide bonds form between the 2 adjacent AA (enzymes catalyses it).

    4) Ribosome moves along mRNA and reads another AA. Third tRNA brings another AA and so peptide bonds form between this and the dipeptide.
    First tRNA leaves, and brings another AA.

    5) This continues and so the polypeptide chain grows until the stop codon is reached.
    There is NO complementary tRNA for the following codes: UAA, UAG, UCA. The process is now complete.
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    cAMP - activates proteins by altering their three dimensional structure.

    Mutations
    - Change in the sequence of nucleotides in DNA.

    - Point mutation - One base pair is replaced by another - 'Substitution'.
    e.g. GAG >> GTG
    - Insertion/Deletion mutation - One or more nucleotide pairs is deleted or inserted into a DNA molecule >>> causing a Frameshift.

    - Genetic diseases:
    Cystic Fibrosis - Deletion mutation
    Sickle cell anaemia - Point mutation.

    - Missence - When the base triplet is changed so therefore the AA is changed, changing the protein structure.

    - Nonsense - When the base triplet is changed to a stop codon or if the first base triplet is changed compared to the original, which would stop the polypeptide from being formed.
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    Silent mutation - When the base triplet is changed but still codes for the same AA because of the degenerate code.

    - Corresponding DNA template strand - complementary to the original DNA strand according to the base-pairing rules: A-T, C-G

    - mRNA - Similar to the original DNA strand, but T's replaced with U's.

    - tRNA anticodon for each mRNA codon - Complementary to the original DNA strand, according to the base pairing rules: A-U, C-G, G-C, T-A

    - AA - to find AA use the table (would be given).

    Neutral effects

    When a gene is altered it becomes an allele.
    No change in the organism if:
    - Mutation is in the non-coding strand of the DNA.
    - Silent Mutation (AA still the same).
    - Change in protein structure, which causes a different characteristic. If that specific characteristic has no advantages or disadvantages then it is considered as neutral. e.g. - rolling your tongue.
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    (Original post by student92)
    I've started my revision, even though we haven't even finished learning all the modules in class. Around 3 months to go, need to ace this exam!
    oh **** i do **** i do... Thats the spirit! yep see you in 3 months OCR! XD
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    (Original post by ibysaiyan)
    oh **** i do **** i do... Thats the spirit! yep see you in 3 months OCR! XD
    Haha
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    Beneficial and Harmful effects

    E.g: Darker skin - Melanin protected them from harmful effects of UV.
    - Could synthesise Vit. D
    Paler skin - Burned, suffered from skin cancer.

    In more temperate climates:
    Darker skin - Synthesised less Vit. D due to less sunlight.
    Paler skin - Synthesised more Vit. D.
    >> All dependent on the environment.


    The Lac Operon

    There are 2 types of enzymes:
    - Constitutive enzymes - used in glycolysis.
    - Inducible enzymes - only made when required.

    Lac operon - section of DNA within a bacterium's DNA.



    Structural Genes - Z is for the enzyme Beta-galactosidase and Y is for the enzyme Lactose Permease. Both are inducer enzymes.

    Operator Region (O) - Switches genes on and off. Where Inhibitor binds.

    Promotor Region (P) - Where RNA polymerase binds, starting the process of transcription.

    regulatory genes (I) - not part of the operon.
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    good stuff
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    sorry, just out of curiosity where do u av dem links to files like dis? tanks
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    (Original post by student92)



    Structural Genes - Z is for the enzyme Beta-galactosidase and Y is for the enzyme Lactose Permease. Both are inducer enzymes.

    Operator Region (O) - Switches genes on and off. Where Inhibitor binds.

    Promotor Region (P) - Where RNA polymerase binds, starting the process of transcription.

    Irregulatory genes (I) - not part of the operon.
    wheres the irregulatory gene (I) meant to be on the diagram?
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    (Original post by ACDC)
    wheres the irregulatory gene (I) meant to be on the diagram?
    Its not part of the operon, but it would be attached to the left hand side when lactose is absent - I gene binds to the lac operator and prevents transcription. You'll find out more about it when I write up my other notes.
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    (Original post by ACDC)
    wheres the irregulatory gene (I) meant to be on the diagram?
    and its called the regulatory gene not irregulatory - my mistake. The 'I' stands for inducible.
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    (Original post by oladimeji)
    sorry, just out of curiosity where do u av dem links to files like dis? tanks
    Thanks... files like these??
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    (Original post by student92)
    and its called the regulatory gene not irregulatory - my mistake. The 'I' stands for inducible.
    oh right. so you're just referring to whats labelled as 'R' on the diagram?

    and what is classed as being part of the operon? POZYa?
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    (Original post by ACDC)
    oh right. so you're just referring to whats labelled as 'R' on the diagram?

    and what is classed as being part of the operon? POZYa?
    Yeah it is 'R'. But its called the I gene. And yeah those are classed as the operon: Structural genes - Z, Y, a and the promotor - P, operator - O regions.
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    (Original post by student92)
    Yeah it is 'R'. But its called the I gene. And yeah those are classed as the operon: Structural genes - Z, Y, a and the promotor - P, operator - O regions.



    where does the 'a' come from , i'm sure its not on the OCR book
 
 
 
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