Point Mutations

DNA Mutations
• Mutations are changes to
the genetic information of
the cell. There are 2
different types of
– large scale – Chromosome
• deletions, inversions,
translocations, & polyploidy
– point mutations – single
• Each mutation carries with
it the ability to alter the
phenotype of the individual
and, if in the cells that
create the gametes, all the
offspring of the individual.
Point Mutations
• base-pair substitutions
– silent mutation - substitution that leads to the same AA
• has no phenotypic effect on the individual
• ex: DNA 3'-CCG-5' changes to 3'-CCA-5'
• ex: RNA 5'-GGC-3' changes to 5'-GGU-3', both code for Glycine
Point Mutations
– missense mutation - change in a base pair that leads
to a new AA
• can improve protein function or render it useless (most
often deleterious - sickle-cell anemia)
• ex: DNA 3'-CCG-5' changes to 3'-TCG-5'
• ex: RNA 5'-GGC-3' Gly changes to 5'-AGC-3' Ser
Point Mutations
– nonsense mutation - changes an AA to a stop
• most often deleterious leading to a truncated (shortened)
protein segment
• ex: DNA 3'-TTC-5' changes to 3'-ATC-5'
• ex: RNA 5'-AAG-3' Lys changes to 5'-UAG-3' Stop
Point Mutations
• Insertions & Deletions
– lead to frame shifts if the insertion or deletion if it is in
an exon
• these mutations are almost always disastrous to the protein
being formed as it changes all codons down stream
• physical and chemical agents that cause a change in DNA
– physical - radiation
– chemical - classified as carcinogens
• Teratogen – leading to birth defects of the fetus