mutations and gene expression

• Mutations


  Changes to the Base Sequence of DNA
• Mutations


  • Any change to the base code of DNA
  • Can be caused by errors during DNA replication
  • The rate of mutation can be increased by mutagenic agents
• Types of mutations

  • Substitution
  • Deletion
  • Addition
  • Duplication
  • Inversion
  • Translocation
• Substitution


  One or more bases are replaced by others (e.g. ATCCCT becomes ATCCT)
• Deletion


  One or more bases are removed (e.g. ATCCCT becomes ATCCT)
• Addition


  An extra base is added (e.g. ATGCCT becomes ATGACCT)
• Duplication


  Some bases are repeated (e.g. ATGCCT becomes ATGCCCT)
• Inversion


  A sequence of bases is reversed (e.g. ATCCCT becomes ACCGTT)
• Translocation


  A sequence of bases is moved from one location to another
• DNA sequence


  Determines the sequence of amino acids in a polypeptide
• If a mutation occurs in a gene, the sequence of amino acids in the polypeptide that it codes for could be different</b>
• Changes to the amino acid sequence of a polypeptide may change the 3D shape of the protein, which could mean that it doesn't work properly
• Some mutations can cause genetic disorders or increase the likelihood of developing certain cancers
• Hereditary mutations are passed on to offspring
• Not all mutations affect the order of amino acids
• The degenerate nature of the genetic code means that some amino acids are coded for by more than one DNA triplet
• Some substitutions will code for the same amino acid
• Inversion mutations don't cause a change in the amino acid sequence
• Mutagenic agents


  • Can increase the rate of mutation
  • Can act as base analogs, altering bases during DNA replication
  • Can delete or alter bases
  • Can change the structure of DNA
• Common mutagenic agents


  • Base analogs (e.g. 5-bromouracil)
  • Alkylating agents
  • UV radiation
• Cancer


  A disease that affects weak and people of all ages. There are lots of types of cancer with potentially devastating effects on how the body functions.
• Mutations in Genes Can Cause Uncontrolled Cell Growth


  1. Means that occur in individual cells after birth in adulthood are called acquired mutations

  2. Mutations occur in the genes that control the rate of cell division and can cause uncontrolled cell division

  3. Rapid cell division results in a mass of abnormal cells
• Tumour suppressor genes


  Genes that control cell division
• Proto-oncogenes


  Genes that can become cancer-causing if mutated
• Inactivation of tumour suppressor genes


  1. Mutations in the DNA sequence

  2. Effect of a proto-oncogene can be increased

  3. A mutated proto-oncogene is called an oncogene
• Abnormal Methylation


  Methylation is a process that controls gene expression
• Hypermethylation of tumour suppressor genes


  They are not transcribed, allowing cells to divide uncontrollably
• Hypomethylation of proto-oncogenes


  Increases production of proteins that encourage cell division, causing uncontrolled growth
• Increased oestrogen may contribute to some breast cancers
• Oestrogen can stimulate breast cells to divide and replicate, increasing chance of mutations
• Oestrogen may be able to directly introduce mutations into breast cell DNA
• Tumour


  A mass of abnormal cells
• Malignant tumours


  • Cancerous, usually grow rapidly and invade/destroy surrounding tissue
  • Cells can spread to other parts of the body
• Benign tumours


  • Not cancerous, usually grow slower and are often encased in connective tissue
  • Can cause blockages and put pressure on organs
  • Some can become malignant
• Tumour cells


  • Irregular shape
  • Larger and darker nucleus, sometimes multiple nuclei
  • Don't produce all needed proteins
  • Different surface antigens
  • Don't respond to growth regulation
  • Divide more frequently than normal cells
• Genetic and Environmental Factors Affect the Risk of Cancer
• There are many risk factors that can increase the chance of getting cancer. These can be either genetic or environmental.
• Genetic factors


  Some cancers are linked to specific inherited alleles. Having these alleles increases the likelihood of getting that type of cancer, but does not mean you will definitely get it.
• Environmental factors


  Exposure to radiation, lifestyle choices like smoking, and diet have all been linked to an increased chance of developing cancer.
• It is difficult to interpret the relative contributions of genes and environment to cancer risk.