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Order of molecules during transcription

  1. Mar 22, 2017 #1
    I wonder if this is a viable question:

    During transcription processes, which molecule in genes is "first in line", the phosphate group or the ribose sugar? I know they line up interchangeably, but does one of them "start" the process first?

    I guess I could ask the same thing about proteins when they are made, whether carboxyl or amino group comes first in line?
     
  2. jcsd
  3. Mar 22, 2017 #2

    Ygggdrasil

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    Phosphate and ribose are part of the same nucleotide molecule, so they get added simultaneously to RNA during transcription. There is a polarity to RNA synthesis, however. Nucleotides get linked together by a phosphodiester bond bridging carbon 5 from the ribose of one nucleotide to carbon 3 from the ribose of another nucleotide. These carbons are referred to as the 5' (five prime) and 3' (three prime) carbons to differentiate them from carbon 5 or 3 on the nitrogenous bases. When new nucleotides are added to a growing mRNA strand, RNA polymerase links the 3' end of the existing mRNA molecule to the 5' end of the new nucleotide.

    Similarly, the amino- and carboxy- ends of amino acids are part of the same amino acid molecule, so they get added to proteins simultaneously. However, proteins are synthesized from the amino-terminus to carboxy-terminus (i.e. the amine group of a new amino acid gets linked to the carboxyl group of the growing polypeptide chain).
     
  4. Mar 22, 2017 #3
    Perfect, exactly what I asked, many thanks Ygggdrasil!
     
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