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    What time is the AQA AS biology exam?
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    Alright, well I just drowned a woodlouse + I've got crackers + cheese now so I'm feeling a little better.

    Let's do this. No more breaks, Anon.
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    (Original post by Haroon55)
    What time is the AQA AS biology exam?
    Anyone?
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    Structure of DNA - Topic 3.

    The double-helix structure of DNA, enabling it to act as a stable information-carrying molecule, in terms of:
    •the components of DNA nucleotides:deoxyribose,phosphat e and the bases adenine, cytosine, guanine and thymine
    • two sugar-phosphate backbones held together by hydrogen bonds between base pairs
    • specific base pairing.
    DNA (Deoxyribosenucleicacid)

    DNA is a macromolecule made up of repeating units called nucleotides. This is what makes DNA a polymer. The nucleotides are each made up of three molecules linked together.


    Sugar- Base(nitrogen)- Phosphate.

    Okay, so the diagram is a little pentagon thingy and you've got to remember that the complementary base pairs are Adenine + Thymine. And Guanine and Cytosine.

    GC = 3 Hydrogen bonds.
    AT = 2 Hydrogen bonds.

    Nucleotides join together to form polynucleotide strands. The type of reaction joining a base, phosphate and sugar is called condensation. O_O Two water molecules are released.

    The strands are orientated opposite to each other. The 'start'/'top' of one strand is paired with the 'end'/bottom' of the other. The two strands are said to be anti parallel.

    The covalent bonds holding the nucleotides together in each strand are stronger than the hydrogen bonds. The strong covalent bonds ensure that the structure of each strand is stable. The hydrogen bonds are much weaker and allow the two strands to be seperated easily.

    DNA is passed onto:

    - The next generation of cells (daughter cells) when cells in the body divide to bring about growth/repair.

    - The next generation of individuals.

    When passing on DNA to daughter cells, the DNA in the parent cells is replicated so that the daughter cells are genetically identical to each other and the parent cell.
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    (Original post by Haroon55)
    Anyone?
    There's a reason why you're supplied with an exam timetable.

    I'm an A2 Student therefore I've no idea + this isn't a Biology chat thread.
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    Okay, I'm going to read through the power point now and also make my notes.
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    (Original post by Haroon55)
    Anyone?
    Afternoon im pretty sure. Check the website.

    Good Luck Anon, try not to panic :x. I believe in yoooooou

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    (Original post by Anon_98)
    There's a reason why you're supplied with an exam timetable.

    I'm an A2 Student therefore I've no idea + this isn't a Biology chat thread.
    Lol I know, our college is disorganised, what do you expect if it's the first year in which it started doing a levels and from what I can see seems like your doing the same exam.
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    I've just finished making some small flashcard type things and I've read through the PowerPoint and memorised the stuff.

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    (Original post by Thomith)
    Afternoon im pretty sure. Check the website.

    Good Luck Anon, try not to panic :x. I believe in yoooooou

    Posted from TSR Mobile
    Thank you
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    Genes + Polypeptides. - Topic 4.

    geneoccupiesafixedposition,calle dalocus,onaparticularstrandofDNA .GenesaresectionsofDNAthatcontai ncodedinformationasaspecificsequ enceof bases. Genes code for polypeptides that determine the nature and development of organisms. The base sequence of a gene can change as a result of a mutation, producing one or more alleles of the same gene.Asequenceofthreebases,calle datriplet,codesforaspecificamino acid.Thebase sequence of a gene determines the amino acid sequence in a polypeptide. In eukaryotes, much of the nuclear DNA does not code for polypeptides. There are, for example, introns within genes and multiple repeats between genes. Differences in base sequences of alleles of a single gene may result in non-functional proteins, including non-functional enzymes.
    Ew, the layout is all messed up in that ..but whatever.

    Okay,

    Gene locus. - A fixed position on a gene.

    Each protein is made from one or more polypeptide chains. A polypeptide contains many amino acids linked together by peptide bonds. The sequence of the amino acids in a polypeptide chain is determined by the sequence of the bases in the gene that directs the synthesis of that polypeptide. Each triplet of bases codes for one amino acid.

    When a gene is being used to direct the production of it's encoded polypeptide, it's base sequence is copied to a smaller molecule, called mRNA. Unlike DNA, mRNA can leave the nucleus via a pore in the nuclear envelope. It's code is used by ribosomes to make polypeptide chains with the encoded sequence of amino acids.

    Non coding DNA.

    There are sequences of bases called Introns that do not code for any of the amino acids in the final polypeptide chain. The coding regions are called exons.

    When the base sequence of a gene is copied to mRNA, the introns are removed from the mRNA molecule before it leaves the nucleus. There are also base sequences between genes that do not code for amino acids. They often contain repeating trinucleotides containg cytosine and guanine, for example, CAG or CGG. These multiple repeats are called minisatellitles or microsatellites.

    A great number of these micro/mini satellites occur in the human genome and each is extremely variable between individuals. The variability of minisatelillteilslsleee DNA and microsatellite DNA is the basis of genetic fingerprinting.
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    Not sure where to put this under so I'll just write it out here as extra info.

    Gene mutations.

    A gene mutation is a change in the base sequence of a DNA molecule. Different base sequences of the same gene are called alleles of that gene.

    Even the smallest mutation can have a significant effect as it may result in a change in the primary structure of the protein produced, as it changes the triplet that codes for one of the amino acids. Point mutations affect just one base in the DNA molecule.
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    Hm.. I don't think I need to make notes on this bc it's in my head after I wrote it out. I'm now going to read through the PowerPoint then move onto the next topic.
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    (Original post by Anon_98)
    Hm.. I don't think I need to make notes on this bc it's in my head after I wrote it out. I'm now going to read through the PowerPoint then move onto the next topic.

    There is thread from ORDO for this exam tomorrow. Can you post the notes there so everyone who resitting can benefit from ur notes thanks

    http://www.thestudentroom.co.uk/show....php?t=4122319
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    DNA and Chromosomes.- Topic 5.

    In eukaryotes, DNA is linear and associated with proteins. In prokaryotes, DNA molecules are smaller, circular and are not associated with proteins.
    Not sure what else I can do with that piece of information..

    Eukaryotes. = associated = LINEAR. = ----------------------------------------

    Prokaryotes= dissociated = CIRCULAR. = 0 0 0 0 0 0 0 0 0 0 0 0 00 0 0

    ~

    lol.

    Alright, Topic 6.
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    (Original post by Anon_98)
    DNA and Chromosomes.- Topic 5.



    Not sure what else I can do with that piece of information..

    Eukaryotes. = associated = LINEAR. = ----------------------------------------

    Prokaryotes= dissociated = CIRCULAR. = 0 0 0 0 0 0 0 0 0 0 0 0 00 0 0

    ~

    lol.

    Alright, Topic 6.
    You are doing really well. Also try looking for this doc on tsr with all the mark scheme answers in it. You can just learn it or evwn have a look at it after going through your notes. I'll see if i can find it for you
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    (Original post by Sooliga)
    There is thread from ORDO for this exam tomorrow. Can you post the notes there so everyone who resitting can benefit from ur notes thanks

    http://www.thestudentroom.co.uk/show....php?t=4122319
    Hm, alright what notes do you mean? The ones in this thread? Sure, I'll post a link.

    If you mean the ones that I have at home, I've barely made any + I doubt they'd be legible anyway bc they're handwritten + my handwriting is awful. Plus, I don't want to waste time and that'd waste time and I don't have enough time to waste. They're not v good anyway so I honestly don't think anyone would benefit from them, as such.
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    (Original post by TheTeresaLover)
    You are doing really well. Also try looking for this doc on tsr with all the mark scheme answers in it. You can just learn it or evwn have a look at it after going through your notes. I'll see if i can find it for you
    Thank you so much for the encouragement. <3 + thanks, I didn't know there was one. - I don't want to distract you from your revision though, if you're busy then I'll try and look for it after I've finished everything.
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    Meiosis - Topic 6.

    A meiotic cell division involves two divisions of the nucleus and two division of the cell.

    - Meiosis I separates the chromosomes from each homologous pair into different cells, halving the chromosome number.

    - Meiosis II separates the chromatids in each chromosomes, like mitosis.

    The main stages of Meiosis I

    Early prophase I
    Late prophase I
    Metaphase I
    Anaphase I
    Telophase I
    Cytokinesisssss.

    ~

    Early prophase. - The DNA has already replicated and each chromosome consists of two chromatids. The cell contains two sets of chromosomes.

    Late prophase - The spindle starts to form. Homologous chromosomes pair up forming bivalents and exchange DNA between non sister chromatids.

    Metaphase I - The spindle is complete and the nuclear envelope has disintegrated. The bivalents are arranged around the middle of the spindle.

    Anaphase I - Homologous chromosomes start to seperate from each other.

    Telophase I - There is one complete set of chromosomes at each end of the cell.

    Cytokinesis.- The cytoplasm divides and two identical daughter cells are formed. The two cells resulting from meiosis I are therefore haploid.


    Ummm, okay- I'm going to try and memorise this then write about crossing over + random segregation + Meiosis II.
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    (Original post by Anon_98)
    Thank you so much for the encouragement. <3 + thanks, I didn't know there was one. - I don't want to distract you from your revision though, if you're busy then I'll try and look for it after I've finished everything.
    That is really thoughtful of you! I think i have found it. Hopefully its been attached (i still dont know how to use tsr properly)
 
 
 
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