Mutations

• Mutation

  A permanent change in the DNA of a cell
• Types of mutation

  Chromosomal mutations and point mutations
• Categories of point mutations

  • Substitution
  • Deletion
  • Insertion
• What is a substitution point mutation

  
  

  One nucleotide is swapped for another
• Example of a Base Pair Substitution with severe consequences

  • Sickle Cell Anaemia
• Sickle Cell Anaemia

  A single nucleotide substitution in haemoglobin has a large negative effect
• Causes of mutation

  • Spontaneous
  • Induced
• Chemical mutagens

  • Base analogues
  • Modifying agents
  • Intercalating agents
• Physical mutagens

  • Ionising radiation (e.g. X-rays)
  • Ultraviolet (UV) radiation
• What is a chromosomal mutation

  A change in the number or structure of a chromosome
• What is a point mutation

  A change in the nucleotide sequence which affects one base.
• What type of mutations are inhertitable

  Mutations in the germ-line
• what type of mutations are non-inhertable

  Mutations in somatic tissue
• What is an insertion mutation

  One nucleotide is added to the base sequence
• What is a deletion point mutation

  One nucleotide is removed from the nucleotide sequencce
• Why do substitution point mutations have little to no effect

  The genetic code is redundant.
• what is a missense substituiton mutaiont

  The substitution produces a codon which changes the amino acid
• what is a nonsense subsitution mutation

  The codon produced codes for a stop protein.
• What are the effects that a point mutation can cause

  Missense. Nonsense. Null mutation.
• What is a null mutation

  when the change in sequence produces a start stop sequence.
• What is a frameshift

  When an insertion or deletion changes the reading frame.
• What causes a frame shift

  Insertion or deletion mutations.
• What are sponatenous mutations

  They are replication errors.
• What is Tautoerism

  A spontaneous mutation which changes a base pair to its imino form.
• What is the imino form of a base

  The form which has a different number of Hydrogen bonds.
• What is the effect of tautomerism

  Results in a mismatched base pair due to the change in the number of hydrogen bonds. Results in an incorrect nucleotide sequence [mutation].
• What are induced mutation cuases

  These are called mutagens. They can be chemical or physical.
• What are the two types of modifying mutagens

  Deaminates and alkylates.
• What is a base analogues

  A substance that resembles a base but pair incorrectly when incorporated into DNA. This results in a point mutation.
• What are deaminiation mutagens.

  The removal of the amino group from Cytosine or Adenine. The form produced resembles another base, resulting in a point mutation.
• What are alkylation mutagens

  The addition of an HC group removes hydrogen bonds, resulting in the incorrect pairing of bases. This results in a point mutation.
• What are intercalating mutagens

  Agents that distort the DNA helix resulting in a frameshift.
• How does Ultraviolet radiation result in mutations

  Produces pyrimidine dimers in which the adjacent bases are covalently bonded. This interrupts DNA synthesis.
• How does ionising radiation result in mutations

  Ionises DNA or water to produce radicals. Radicals damage bases, causing the double strand to break.
• What is the cell's mechanism to deal with double-strand breaks

  The cell cycle arrests or undergoes apoptosis.
• How is DNA repaired

  Nucleotide excision repair recognises distortions in the DNA helix. Nuclease cuts out the damaged DNA. DNA polymerase resynthesizes and fills the gap. DNA ligase seals the strands together.
• What is a pre-disposition to cancer

  Cancers caused by germ-line mutations.
• How are mutagens identified

  Ames test.
• Describe the ames test.

  Rat liver extract is mixed with a salmonella strain, which requires histidine. Possible mutagen is added.

  The solution is incubated on a plate which lacks histidine.

  A high number of revertants after incubation suggests that the substance is a mutagen.
• What is seen on the control plate for an ames test

  Little growth of revertants.