Biology: mutations, cancer

• what is a gene mutation and where does is happen?

  happen in the nucleotide base sequence of DNA and can occur spontaneously during DNA replication (during S-phase)
• Substitution: one base is exchanged for another
• Deletion: a base is lost (reduces the number of bases)
• Insertion: a base is added (increases the number of bases in a gene)
• if these mutations result in a change in the amino acid coded for by the DNA, there will be a change in the mRNA codon which results in a different tRNA being bought to the ribosome which alters the primary structure of a protein
• Hereditary Gene Mutation


  only happen if the gene mutates in the DNA of cells of the gamete

  inherited by the next generation

  can be known as gremlin mutations

  may not affect the person but possibly their offspring
• Acquired Gene Mutation


  not present at birth

  only present in certain cells

  could be due to environmental factors

  sometimes known as somatic mutations

  cannot be inherited by offspring
• Benign


  not cancerous

  encapsulated by connective tissue

  slower growing

  do not metastasise
• Malignant


  cancerous

  fast growing

  non-capsulated

  metastasise
• what does 'metastasise' mean

  when parts of the tumour spread to other parts of the body
• a proto-oncogene stimulates cell division
• a tumour suppressor gene codes for proteins which inhibit cell division
• if a DNA mutation occurs in a proto-oncogene it becomes an oncogene and results in an over-stimulation of cell division and produces a protein which causes cancer
• if a DNA mutation occurs in a tumour-suppressor gene, the gene becomes inactivated and stops inhibiting cell division so the cell division increases and there is no control over the cell cycle
• damage to DNA in a cell can cause mutation in the DNA code.

  if the mutation is in a tumour suppressor gene or a proto-oncogene, this would disrupt the regulation of the cell cycle

  the cell may then divide uncontrollably and not undergo programmed cell death (apoptosis) when it should

  this would lead to the formation of a tumour
• chemotherapy 


  drugs are used to destroy cancer cells

  can also harm healthy cells

  used to cure, control and ease symptoms
• radiotherapy 


  high energy radiation is used to shrink tumours and kill cancer cells by damaging their DNA
• cryosurgery 


  used on external tumours, retina, cervix and early stage prostate cancer

  liquid nitrogen

  dissolves and forms a scab

  can affect fertility and cause scarring
• genetic testing and screening is used to detect the presence of a particular genetic disorder
• taking a sample of DNA can be either:

  1. cheek swab
  2. blood sample
• limitations of genetic testing and screening

  1. chemicals used to prevent blood clotting when taking a DNA sample can affect the quality of DNA
  2. if a genetic disease requires testing of several genes, a larger sample of DNA may be needed than is available
  3. interpreting results may require other blood samples from family members for comparison
• advantages of genetic screening and testing

  1. a sense of relief
  2. increased knowledge about risk
  3. help make informed medical and lifestyle changes
• genetic screening


  used to identify a persons risk

  DNA is taken from the patient (cheek swab or blood sample)

  DNA is then sequenced and read in a lab

  the DNA sequence is then checked against known alleles for a particular condition
• DNA


  Deoxyribonucleic acid, contains genetic instructions
• Tumour suppressor gene


  A type of gene that helps to regulate the cell cycle and prevent uncontrolled cell growth
• Proto-oncogene


  A type of gene that, when mutated, can become an oncogene, promoting cell growth and division
• Cell cycle


  The sequence of events that occur in a cell as it grows, replicates its DNA, and divides
• Apoptosis


  Programmed cell death, a process in which a cell self-destructs