The genetic code, transcription and translation

The genetic code

As we know, DNA is our very own instruction booklet for cells. It provides the outlines for all the proteins we could possibly need. Proteins are made from strings of amino acids. We have 20 amino acids at hand and yet we can produce thousands of different proteins. How? Through the magic of transcription and translation.

For now, you need to know the following things:

  • Base triplets of DNA (codons) are 3 paired up bases (eg. CCG, AGC) that encode for 1 amino acid
    • Side note: The reason for a triplet is to allow all 20 amino acids to be encoded for separately. If it were a pair of 2 you could only have 16 combinations. Having 3 means you get a whopping 64 combinations, meaning some base triplets encode for the same protein or have no function. BUT this still means each base triplet encodes for 1 amino acid.

 

  • The genetic code is:
    • Universal – same bases among species, different orders (aliens though… Who knows!)
    • Non-overlapping – ATGCTA would encode as ATG + CTA
      • Overlap -> ATG, TGC, GCT etc.
    • Degenerate – amino acids can be encoded by multiple base triplets (due to having too many like I said before)

 

  • tRNA and mRNA structure and comparisons with DNA

 

Transcription

transcription.pngDNA is normally tightly wound up in the nucleus of cells. During transcription, RNA polymerase (an enzyme) unzips, allowing for complementary base pairing and zips up the DNA again when finished. Free bases are found floating in the nucleus that match up to the genetic code of DNA when needed, like in transcription. Here, a pre-mRNA molecule is formed that detaches and undergoes splicing to remove useless introns (they’re just regulatory bits of code that the DNA uses, they don’t encode for proteins). It then moves out of the nucleus and into the cytoplasm for translation.

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