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DNA Structure and Function

Biology (Year 12)

Proteins

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Ben Whitten


Image: Heat shock protein 70 image, Image by CAChamblee, Sourced Under a Creative Commons 4.0 License from Wiki Commons Proteins are one of the four main biological molecules which are built from a selection of 20 different amino acids. These amino acids are linked together by peptide bonds to form polypeptide chains, which fold and/or are modified in order to form the protein. The sequence of amino acids in a polypeptide is determined by the sequence of mRNA codons in a strand of mRNA. If the sequence of codons is known, the sequence of amino acids can be determined from an amino acid table.

Image: Amino Acid Codon Table image, Image by Scott Henry Maxwell, Sourced Under a Creative Commons 4.0 License from Wiki Commons The amino acid table tells us which amino acid a specific codon actually codes for. There are 64 possible base triplets, where 1 of them is the start codon (AUG), and 3 of them are stop codons (UAG, UAA, UGA). The three nitrogenous bases in a codon code for an amino acid, for example. CUA codes for leucine, or Leu. Amino acids are abbreviated by three letters. You won't be required to memorise all of these amino acids, but may need to interpret an amino acid table. The order it is read in is the left axis is first, then the top, and the right axis. For example, let's say we are provided with a sequence; AUG UCA GUC ACU UAC UAG

This sequence translates to;

Met-Ser-Val-Thr-Tyr-STOP (or in their longer forms, methionine, serine, valine, threonine, tyrosine, STOP)

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