DNA mutations

• Mutation


  A change in the DNA base sequence
• Mutations happen spontaneously in our cells all the time, particularly when DNA is being duplicated before cell division like in mitosis
• Things that increase the risk of mutations

  • Carcinogens (harmful chemicals like in cigarette smoke)
  • Certain types of radiation (like x-rays or gamma rays)
• These things don't always cause mutations, they just increase the risk of a mutation occurring
• Gene


  A section of DNA that codes for protein
• Triplet/Codon


  A group of 3 bases that codes for one of the 20 different amino acids
• How DNA works to create proteins

  1. Triplets/codons code for amino acids

  2. Amino acids combine in the correct order to form a protein chain

  3. Protein chain folds to form a protein
• A mutation that changes a single base can change the amino acid that the codon codes for, which can have knock-on effects on the protein structure and function
• Most mutations don't have a significant effect, either because they only slightly affect the protein or because they occur in non-coding DNA that doesn't code for proteins
• Non-coding DNA


  DNA that isn't part of any gene and doesn't code for protein, but can play a role in gene expression
• Types of mutations


  • Substitutions
  • Insertions
  • Deletions
• Substitution mutation


  One base is changed for another
• Insertion mutation


  An extra base is inserted into the sequence
• Deletion mutation


  One base is deleted from the sequence
• Insertion and deletion mutations are worse than substitution mutations because they shift the subsequent codons, completely changing the amino acid sequence