• Question: One base makes 4 amino acids? How? This was not explained in the first lecture, or did I miss something. What determines that 1 base can make 4 amino acids? especially as in DNA works using amino acid pairs.

    Asked by richyhem to Sara, John Robert, Gemma, Connie, Becky, Alison on 20 Jan 2014.
    • Photo: Gemma Swiers

      Gemma Swiers answered on 20 Jan 2014:

      It isn’t possible for one base to make one amino acid. There are 4 bases, Adenine (A), Guanine (G), Cytosine (C) and Thymine (T). A always pairs with T and G always pairs with C. There are 20 amino acids. Alison explained in the lecture that if one base made one amino acid we would only be able to make 4 amino acids. If 2 bases made up an amino acid then we would only get 16 amino acids, so there needs to be 3 bases (we call this a triplicate codon) to make one amino acid.

      In fact some amino acids are made up from more than one combination of 3 bases. The amino acid Methionine is made of the bases ATG but the amino acid Lysine can be made from two triplicate codons, AAG and AAA. Other amino acids like Proline can be made from 4 triplicate codons CCT, CCC, CCA and CCG all make the amino acid proline.
      I hope this answers your question!

    • Photo: John Robert Davis

      John Robert Davis answered on 20 Jan 2014:

      Hey richyhem,

      I hope this answers your question. DNA is a code made of four nucleotides (also known as base pairs) which code for 20 amino acids. Amino acids join together to form proteins which perform the tasks cells need to survive, metabolise and grow. It is therefore important that proteins are made of the correct amino acid sequence.

      In order for the correct amino acid sequence to form there needs to be a specific series of base pairs for each amino acid. It is a bit like a bar code in a supermarket. In order for the till to known that you are buying a Boost chocolate bar and not a Kit-Kat you need a specific bar code unique for both.

      If amino acids were coded by a single base, then for each base you could have 5 amino acids. It would be very unlikely you would ever make the correct protein. If two base pairs coded for amino acids then each possible sequence of base pairs (8 possible sequences in total) could code for 2.5 amino acids. This would make it more likely to get the protein you want but would still involve a bit of pot-luck.

      But if three base pairs coded for an amino acid then there would be 64 possible sequences. Therefore each amino acid could have a specific code, its very own bar-code. And this is what happens, you need three base pairs to code for one amino acid. Allowing you to make the correct protein every-time.