Mutations Changes in the nucleotide sequence of DNA

Mutations Changes in the nucleotide sequence of DNA or m. RNA

Mutations • Changes in the nucleotide sequence of DNA or RNA that code for a protein • Mutations are caused by mutagens (means “to generate a mutation”) – Examples: • • UV Radiation Cigarette Smoke Viruses Chemicals: Laboratory, pesticides, insecticides

Point Mutations • One nucleotide base is replaced with another (A single nucleotide mutates thus affecting one codon. ) It’s like changing one “word” in a DNA sentence.

• Silent Point Mutation – This is a harmless mutation. Since many amino acids have multiple codons, it is possible that a mutated codon will still translate into a correct amino acid. • For Example – Original Sequence: G A A G A G m. RNA: C U U C U C Amino Acids: Leu

• Missense Point Mutation – This mutation changes the amino acid coded for (MIStake). This is seen in the mutation that causes Sickle Cell Anemia • For Example – Original Sequence: C T T C A T m. RNA: G A A G U A Amino Acids: Glu Val

Sickle Cell Anemia

Frameshift Mutations • These mutations alter the codon sequence and shift the ‘reading frame’ (A reading frame is a set of 3 consecutive nucleotides (codon) read in the 5’ 3’ direction). • It’s like changing the DNA “sentence. ” Frameshift mutations are normally very serious. If the codons aren’t read correctly, they will be translated into incorrect amino acids and make nonfunctional proteins.

• Insertion: adding nucleotides to the sequence – Original sequence: THE BIG TAN DOG RAN – Original with Insertion: THE BOI GTA NDO GRA N • For Example – Original Sequence: CAT TGA CAT ATG A m. RNA codons: GUA ACU GUA UAC U Amino Acids: Val Thr Val Tyr --

• Deletion: taking nucleotides out of the sequence – Original sequence: THE BIG TAN DOG RAN – Original with Deletion: THE BGT AND OGR AN • For Example: – Original Sequence: CAT TGA CTT GA m. RNA codons: GUA ACU GAA CU Amino Acids: Val Thr Glu --

Chromosomal Mutations • Mutations in chromosome structure – Deletion: sections of the chromosome are missing – Duplication: sections of a chromosome are repeated

Mutations in Chromosome Number • Monosomy: only one copy of a chromosome – Turner Syndrome: when a female has only one X chromosome. Females with this condition have short stature, are sterile and have other physical abnormalities.

• Trisomy: one extra copy of a particular chromosome (three copies total) – Down Syndrome (trisomy 21): mental retardation, short stature, wide set eyes

Who is Affected? • Somatic Cells – If a mutation happens in a body cell, only the person that the mutation occurred to will be affected – Mutations in body cells can lead to cancer • Gametes – If a mutation happens in a sex cell, only the organism created from that sex cell will be affected. – Mutations in sex cells affect future generations and this is a cause of evolution, i. e. change in DNA over time