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I haven’t been able to confirm this anywhere. If this were not the case, when transcription occurred, if the transcription were based upon the incorrect side of the DNA molecule, a completely incorrect output would result. Complementary sides should be aliases of each other, but I have not been able to find anywhere whether this is the case.

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    $\begingroup$ Isn't this trivial to answer using a chart of the genetic code? How do you think transcription would start on the "wrong" side? $\endgroup$
    – Bryan Krause
    Jun 8 at 22:33
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    $\begingroup$ Welcome to the site. Please take a tour and visit the help center to find information on what we do here. In particular pay attention to the homework policy, which would cover your question. You could self-answer your question by thinking about strandedness and direction of transcription! $\endgroup$
    – bob1
    Jun 8 at 22:34
  • $\begingroup$ @BryanKrause In the very least, in this image, the sequence UUU does not produce the same results as AAA: ars.els-cdn.com/content/image/… $\endgroup$ Jun 8 at 22:46
  • $\begingroup$ “Complementary sides should be aliases of each other” — are you assuming that complementary strands should produce the same proteins when transcribed and translated? Why do you believe this to be true? $\endgroup$
    – acvill
    Jun 8 at 22:51
  • $\begingroup$ If DNA intends to code for one set of amino acids, would it not be wrong for a ribosome to build a polypeptide from different amino acids than one side of the DNA molecule intended for? Essentially, if one side of the DNA molecule depends on the other side of the DNA molecule, why would it ever be the case that complementary sequences don’t produce the same amino acid outputs? Since DNA is symmetric, I don’t see how the ribosome would be able to determine which side is intended to hold the information, in the case that complementary bases within codons don’t code for the same bases. $\endgroup$ Jun 8 at 22:53

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Transcription is a highly regulated process, cells aren't just producing random RNAs from random stretches of DNA.

The transcription machinery needs to bind to DNA to get started, which requires a promotor sequence. It's not necessary for DNA to "read" the same way forwards and back, because it'll only be transcribed in the correct direction.

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    $\begingroup$ My question is not about the direction of transcription and translation, but rather, which side of the molecule the process begins copying from (i.e. not along the molecule, but across to the mirror side). If one side’s sequence deterministically depends on the other’s, is it the case that either side (i.e. codons containing exactly complementary bases) would produce the same output? If not, then why? Is there some way of ensuring that only one side of the mirrored DNA structure is read? $\endgroup$ Jun 8 at 23:03
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    $\begingroup$ Yes, only that side "fits". DNA is directional (the ends are referred to as 5' and 3' ends). If you read the whole Wikipedia page on transcription or an equivalent chapter in a biology textbook I think it'll become clear. If you wanted to transcribe the other side, you'd have to start at the "end" and work backwards. $\endgroup$
    – Bryan Krause
    Jun 8 at 23:12
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    $\begingroup$ Thank you. I think this directionality shows me where the cracks of my question lies. $\endgroup$ Jun 8 at 23:18

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