Gene expression and mutation

• Gene expression


  When a gene codes for a protein that is synthesised in the cell, the gene is said to be expressed
• Most of the DNA does not actually code for proteins
• There are only 21 000 genes but 3 billion pairs of bases
• Scientists are still discovering what the non-coding part of the DNA does
• Non-coding DNA


  • Involved in switching genes, or parts of genes, on and off
  • Part of the answer to how we can synthesise so many different chemicals with so few genes
  • Each gene can control the synthesis of lots of different proteins
  • Variations in the non-coding areas of our DNA may affect how our genes are expressed
  • This in turn affects the phenotype - the physical appearance or biochemistry of an organism
• Mutation


  Changes in existing genes
• Mutations occur all the time, often as a result of mistakes made in copying the DNA for new cells as they reproduce
• Mutations in coding DNA

  • Most do not alter the protein formed, or alter it so slightly that its appearance and function is not changed
  • A few mutations code for a change in the amino acids that results in an altered protein that folds to give a different shape
  • The changes caused by a mutation may give an advantage eg producing a more efficient enzyme or a stronger structural protein
• Mutations in non-coding DNA

  • Does not directly affect the phenotype
  • Variants in the non-coding DNA can affect which genes are switched on or switched off
  • By changing the genes that are expressed, changes in the non-coding DNA can have a big effect on the phenotype of the organism