6.3: DNA Mutations and Mutagens

Mutations

• permanent change in cells genetic material

• single gene mutations = in one gene, nucleotides

• chromosomal = many genes, chromosomes

• copied through DNA replication, passed down to daughter cells

• in reproductive cells, passed down through generations

Spontaneous

• normally in cells, incorrect base pairing by DNA polymerase

• transposons = short segments of DNA capable of moving within genome (jumping gene)

Induced

• exposure to factors (high energy X-rays, UV) increase rate of mutation

• mutagen = substance or event that increases rate of mutation

  • physical = change DNA structure (X-rays, UV)

  • chemical = molecule that can enter the nucleus of a cell and induce mutations by reacting with DNA

    • similar structure to base pairts

    • nitrites, gasoline, cigarette smoke

Single Gene Mutations

• substitution = 1 base replaces another

  • changes 1 codon in 1 gene

  • silent = gene function altered, does not change amino acid

  • missense = altered amino acid, harmful

  • nonsense = early stop codon, shortens protein or not made

• deletion = 1 base removed

• insertion = 1 base inserted

• changes reading sequence (frameshift mutation)

Chromosomal

• cause rearrangement of genetic material, affects several genes

• deletion = part of chromosome missing

• duplication = extra copies formed

• inversion = segment is broken, re inserted in opposite direction (reverse order)

• translocation = section breaking and fusing to another

DNA Repair

• recognize and repair damage

• specific = looks for specific damage

  • photorepair = mechanism repairs thymine dimer caused by UV radiation

  non specific = removes damaged DNA and replaces with correct sequence