Protein coding

Posted on 2011-10-25
Last Modified: 2012-05-12
The protein-coding strand of the average human gene consists of 1350 nucleotides. Assuming that each nucleotide can take any of four values (A, T, C, or G), how many different genes with exactly 1350 nucelotides are possible ?

Question by:mustish1
    LVL 37

    Expert Comment

    This looks like an academic question so...

    For this type of problem, take the number of possible values and raise it to the power of the number of positions.
    LVL 37

    Expert Comment

    Think about it like this, if there are X possibilities for Y nucleotides, then adding one gives you four times as many options since you can take all of the X possibilities and add either an A, T, C or G.
    LVL 26

    Accepted Solution

    how many different genes with exactly 1350 nucelotides are possible ?

    Are asking about simple numbers of combinations? Or do you want to know how many of those would result in a gene that actually worked to give a useful result? There might be some debate possible about whether or not a combination that destroyed the chromosome could actually be called a "gene".

    LVL 17
    from here:

    Adenine:  One of the four bases in DNA that make up the letters ATGC, adenine is the "A".  The others are “G” for guanine, “C” for cytosine, and “T” for thymine.  Adenine always pairs with thymine.  Cytosine always pairs with guanine.  These letters are used as shorthand for the sequences of fragments of DNA e.g. CCAAGTAC.  These sequences are the code for genetic information.

    If A is always paired with T and C is always paired with G this will reduce the theoretical  number of permutations. Unfortunately the example they show (CCAAGTAC) doesn't seem to conform to the rules they set out in the same paragraph, but I can imagine that a string consisting of 1350 A probably won't be useful.
    LVL 37

    Assisted Solution

    Robin, in DNA when you see a string like "CCAAGTAC," it is referring to one side of the DNA's double helix structure. The other side would then have "GGTTCATG." Any time you see a DNA series, it's only referring to one side.

    Based on mutish1's question history, I'm assuming this is an academic question and it just wants all the possible sequences.
    LVL 17
    Ah yes thanks Tommy. I did read a bit more and saw that. They had only just invented DNA when I was at school, but we did have permutations.

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