Download DNA and mutations

DNA and mutations
SC.912.L.16.4
Mutations
• Alterations in DNA sequence
• Some are part of normal DNA variation
• Caused by chemical and physiological agents
and errors in DNA replication
• Cells can repair some mistakes
• If not repaired, changes in DNA sequence
are made permanent by DNA replication
Point mutations:
Single base mutations:
1. Missense mutation: leads to
an amino acid change
2. Silent mutation: does not
change the amino acid (NO
PHENOTYPIC CHANGE!)
3. Nonsense mutation: causes
premature stop-codon
• Frameshift mutations:
insertion/deletion
duplication
translocation
Altered reading frame
 Severe impacts on protein structure-will see
a phentotypic change, or potentially lethal
Effects of mutations
• Insignificant (no phenotypic change)
1) Some nucleotide substitution mutations
2) Degeneracy of codons
a) More than one codon for most
amino acids
b) Third nucleotide position is often
not important e.g., G-U-n =
valine; U-C-n = serine; C-G-n =
arginine
3) Functional equivalency of amino acids
Effects of mutations
• Harmful
1) Some nucleotide substitutions
2) Nucleotide insertions or deletions
result in frameshifts, null mutations
3) Altered or lost protein function