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    I'm going through the spec for this topic but am struggling to understand a couple of the points... can anyone help?

    1) The occurrence of random spontaneous mutations.
    2) How a gene determines the sequence of amino acids in a polypeptide.

    Thanks!



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    (Original post by Sophie.cerys)
    I'm going through the spec for this topic but am struggling to understand a couple of the points... can anyone help?

    1) The occurrence of random spontaneous mutations.
    2) How a gene determines the sequence of amino acids in a polypeptide.

    Thanks!



    Posted from TSR Mobile
    1. You just need to be aware that mutations are random and what they can result in, ie, a neutral change due to degenerate code, a negative change where the protein is non-functional or a beneficial one where the mutation results in something that helps the organism to survive. At A2 you go into a lot more detail, but judging by the vagueness of the statement, I'm assuming you're AS.
    2. This is to do with transcription and translation, basically how you go from a gene to a protein/polypeptide.
    Hope this helped
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    (Original post by Sophie.cerys)
    I'm going through the spec for this topic but am struggling to understand a couple of the points... can anyone help?

    1) The occurrence of random spontaneous mutations.
    2) How a gene determines the sequence of amino acids in a polypeptide.

    Thanks!



    Posted from TSR Mobile
    1.) spontaneous mutation in terms of nucleic acids means that a purine base in DNA strand (adenine or guanine) got lost and thus the transcription ('reading of the DNA message') is errorneous. It is like some words or even sentences in a book got lost and thus you are not able to understand and so to deal with the message anylonger.

    2.) Do you mean the whole process of transcription and translation I guess? first, the DNA is read to 'decode' the message. After that the message is translated into RNAs (mRNA, tRNA and rRNA) with matching nucleotides. The RNAs are leaving the nucleus then. tRNA has the function to carry an amino acids on to the ribosomes. When the tRNA is transported the amino acid to the ribosomes, the nucleotides of the tRNA (anticodon) and the ones of mRNA (codon) are matching complementarily. The rRNA on ribosomes 'assembles' the mRNA with tRNA. Thus amino acids are forming to polypeptides, so to a protein step by step in this synthesis.

    Hope my ansers wer ehelpful for you. To understand my answer in 2.), here is a picture to my explanation.
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    (Original post by typicalvirgo)
    1. You just need to be aware that mutations are random and what they can result in, ie, a neutral change due to degenerate code, a negative change where the protein is non-functional or a beneficial one where the mutation results in something that helps the organism to survive. At A2 you go into a lot more detail, but judging by the vagueness of the statement, I'm assuming you're AS.
    2. This is to do with transcription and translation, basically how you go from a gene to a protein/polypeptide.
    Hope this helped
    Neutral change may also arise if the amino acids that are changed aren't key to the tertiary structure of the protein, i.e they don't form key bonds and/or aren't present in the active site of the enzyme
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    Remember too that the genetic code is 'redundant', i.e more than one codon codes for each amino acid. There is thus a chance that a mutation in one base would still code for the same amino acid and result in no change in the protein. For instance, a point mutation in the third position of the codon AAU resulting in AAC would have no effect on the resulting protein, since both AAU and AAC code for the same amino acid, asparagine. These are called synonymous substitutions.
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    1 - spontaneous mutations are mutations which occur. These include:

    substitution - a base is replaced with another [mis-sense, nonsense, silent]
    addition - a base is added
    deletion - a base is deleted

    These can arise through various mechanisms in the body - but there's an error rate of roughly 1 in 10^7 base pairs in the human body. Mutations happen randomly, or can occur through lack of proofreading mechanisms in the body - think DNA and RNA Polymerases, if you know what they are. Reactive Oxygen Species and radiation can also play a part - carcinogens/mutagenic agents are prevalent throughout everyone, but mutations also increase with age.

    Genes determine amino acid sequences as the sequence of bases (each codon) 'codes' for one amino acid. Genes code for polypeptides - the gene sequence determines the amino acid sequence. The one thing which needs to be considered is that the processes of transcription, splicing and translation are yet to be fully elucidated, so everything we have is a best fit theory. The idea is that each codon codes for an amino acid, but several codons can code for the same amino acid.

    Also - this is a heavy 'dumbing down' of what I would otherwise say, but you're coming across as a high school/sixth form student.
 
 
 
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