Genetic code

• What are the 3 features of genetic code?

  1 degenerate

  2 universal

  3 non- overlapping
• What is a start codon?

  At the start of every gene there is a start codon TAC in DNA or AUG in mRNA. This code for the amino acid methionine. This is later removed from the protein if it is not actually needed for the structure (initiates translation).
• What is a stop codon?


  At the end of every gene there are 3 bases that don’t code for an amino acid. These mark the end of a polypeptide chain and cause ribosomes to detach and stop translation. These codons are ATT, ATC and ACT on DNA. ( when this happens, translation can no longer occur and synthasis is complete)
• what is a proteome?


  Full range of proteins in one cell, constantly changing depending on what proteins are needed.
• What’s a genome?


  Organisms complete set of DNA in one cell
• What are exons?


  Sections of DNA that don’t code for amino acids
• what are introns?


  Sections of DNA that do not code for amino acids or polypeptide chains. Found in eukaryotic DNA but not prokaryotic DNA. These get removed, spliced out of mRNA molecules
• what does non overlapping mean?

  Each base in a gene is only part of one triplet of bases that codes for one amino acid. So each codon or triplet of bases is read as a discrete unit. It’s an advantage because if a mutation occurs it will only effect one codon so only one amino acid.
• What does universal mean?

  same triplet of bases codes for the same amino acids in all organisms. This makes genetic engineering possible.
• What does degenerate mean?

  there’s 20 amino acids that the genetic code has to be able to code for. There’s 4bases and 3 bases are needed to make enough combinations to code for at least 20 amino acids (4^n). If three bases coded for 1 amino acid this would allow 64 amino acids to be coded for (4x4x4). 64 is more than 20 so as a result each amino acid is coded for by more than one triplet of bases. Genetic code wheel enables you to work out all combinations of bases that code for each of the 20 amino acids. Therefore if mutation occurred it could still code for the same amino acid.