Mutation and variation

• What is meant by a mutation?

  change in sequence bases of DNA
• why is mutation a negative thing?

  protein synthesis can be disrupted if mutation occurs within a gene
• what three ways can a change in sequence occur?

  • substitution (substituting nucleotide(s)/base(s) with other nucleotide(s)/base(s)
  • deletion (eliminating nucleotide(s)/base(s) from a base sequence)
  • insertion (inserting extra nucleotide(s)/base(s) into a base sequence)
• what type of mutation occurs when only one nucleotide is affected?

  point mutation
• What are the effects of substitution mutation?

  • changes the codon in which the mutation occurs
  • if the new codon codes for a different AA this will lead to a change in primary structure of a protein
• why might substitution not affect the primary structure of a protein?

  • genetic code is degenerate
  • which means that multiple codons can code for the same amino acids
  • so the new/mutated codon may still code for the same amino acid
• what are the effects of insertion/deletion mutations?

  • leads to frameshift mutation
  • triplet code means base sequences are transcribed consecutively in non-overlapping groups of three
  • therefore addition/deletion shifts the reading frame of the consecutive bases
  • which will therefore change every successive codon from the point of mutation
• what is the only instance in which insertion or deletion doesn't affect the reading frame?

  • if nucleotides are inserted or deleted in multiples of three
  • the READING FRAME won't be changed, but the PROTEIN FORMED will be affected as a new/multiple AA(s) is/are added or an AA/AAs is/are removed
• state 3 possible results of mutations

  • may have no effect on phenotype because normally functioning proteins are still synthesised
  • damaging- phenotype of organism affected in a negative way as proteins are no longer synthesised/proteins synthesised are non-functional, interferes with essential processes
  • beneficial- new or useful characteristics can be developed in the phenotype
• Describe things which can cause mutations

  • can occur spontaneously during DNA replication
  • rate of mutation is increased by mutagens (mutagen = chemical/physical/biological agent which causes mutation)
  • free radicals (oxidising agents) can affect nucleotide structures and disrupt base pairing during DNA replication
• what are the correct scientific terms to describe the loss of wither a purine or pyrimidine base?

  depurination and depyrimidination
• state three subdivisions of mutations that can occur as a result of mutations

  • SILENT/neutral - protein not changed, no effect on the phenotype. causes changes in primary structure but not overall structure or function of synthesised protein
  • NONSENSE- codon becoming a stop codon instead of coding for an AA. Shortened protein is synthesised which is non-functional. can have negative effects on a phenotype
  • MISSENSE- incorporation of incorrect AA into primary structure of a protein. result depends on the function of the AA being replaced in the structure, can be silent, beneficial or harmful
• what is meant by a conservative mutation?

  when AA change leads to AA being coded for which has the same properties as the original, so the effect of mutation is less severe
• what is meant by a non-conservative mutation?

  new AA coded for has different properties to the original, so more likely to have an effect on protein structure and function, may cause disease
• What are conservative and non conservative mutations examples of?

  Missesne mutations
• what are the three other types of mutation apart from substitution insertion and deletion?

  silent- don’t change any proteins or the activity of the proteins being synthesised

  missense- incorporation of an incorrect AA into the primary structure when the protein is synthesised

  nonsense- a codon becoming a stop codon instead of coding for an AA

  
• describe one example of a beneficial mutation

  ability to digest lactose- majority of mammals become lactose intolerant after they cease to suckle- ability to process lactose helps us prevent diseases (osteoporosis) and starvation during famines
• What’s the difference between gene mutations and chromosome mutations?

  Gene mutations occur in single genes or sections of DNA whereas chromosomal mutation affects the whole chromosome or number of chromosomes within that cell
• State the four types of chromosomal mutations

  • Deletion- a section of chromosome breaks off and is lost within the cell
  • Duplication- sections get duplicated on a chromosome
  • Translocation- a section of one chromosome breaks off and joins another non homologous chromosome
  • Inversion- a section of chromosome breaks off, is reversed and then joins back onto the chromosome