topic 3

• Mutation


  A change in the DNA sequence

  
• DNA replication / S phase / interphase


  The stage of the cell cycle where gene mutations are most likely to occur
• Genetic code is degenerate


  The new triplet code may still code for the same amino acid, even if a gene mutation only affects 1 triplet code
• Frame shift


  When every base shifts position, changing all of the triplet codes downstream of the mutation
• Mutagenic agent


  A factor that increases the mutation rate
• Translocation of bases mutation


  When a section of bases on one chromosome detaches and attaches onto a different chromosome
• Types of gene mutations


  • Addition
  • Deletion
  • Substitution
  • Inversion
  • Duplication
• Stem cell


  Undifferentiated cells that can continually divide and become specialised
• Types of stem cells


  • Totipotent - early mammalian embryo
  • Pluripotent - embryos
  • Multipotent - Mature mammals e.g. bone marrow
  • Unipotent - Mature mammals
• Cardiomyocytes


  Created from unipotent stem cells
• Totipotent stem cells


  During development, they translate only part of their DNA to become specialised cells
• Induced pluripotent stem cells (iPS cells)


  Can be produced from adult somatic cells using appropriate protein transcription factors to overcome some of the ethical issues with using embryonic stem cells
• Transcription factor


  Proteins that can bind to different base sequences on DNA, and therefore initiate transcription of genes

  
• Epigenetics


  Heritable change in gene function, without changing the DNA base sequence

  
• Factors that can cause epigenetic changes


  • Diet
  • Stress
  • Toxins
• DNA methylation


  Increased methylation of DNA inhibits transcription. Methyl groups attach to the cytosine base, preventing transcriptional factors from binding and attracting proteins that condense the DNA-histone complex.

  
• Histone acetylation


  Decreased acetylation of associated histones proteins on DNA inhibits transcription. If acetyl groups are removed, the histones become more positive and are attracted more to the phosphate group on DNA, making the DNA and histones more strongly associated and hard for the transcription factors to bind.

  
• Abnormal methylation and cancer


  Tumour suppressor genes could become hypermethylated, deactivating the gene. Oncogenes could become hypomethylated, permanently switching them on.
• Tumour suppressor gene


  Produces proteins to slow down cell division and cause cell death if DNA copying errors are detected.

  
• Oncogene


  Mutated version of a proto-oncogene, which creates a protein involved in the initiation of DNA replication and mitosis cell division when the body needs new cells. Oncogene mutations can result in this process being permanently activated to make cells divide continually.

  
• Benign tumour


  Can grow very large but at a slow rate, non-cancerous, produce adhesive molecules sticking them together and to a particular tissue, often surrounded by a capsule, can be removed by surgery and rarely return.
• Malignant tumour


  Cancerous, grow large rapidly, cell nucleus becomes large and the cell can become unspecialised again, do not produce adhesive, metastasis occurs, not encapsulated and can grow projections into surrounding tissues and develop its own blood supply.