Mutations
Every now and then cells make mistakes
Inserting incorrect bases
Deleting bases
Adding extra bases
Rearranging genes
Mistakes that cause a change in genetic information are called mutations.
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Mutations
Mutation = a change in the nucleotide sequence (order) of DNA
Possible causes:
Mistakes during DNA replication
Mistakes during cell division
Mutagens = environmental factors that can damage DNA (ex. radiation, chemicals, etc.)
Levels of Mutations
We can study mutations at different levels
DNA
Base pairing rules are not followed
Genes
Point mutation = changes to the base order that affect just one gene
Chromosomal
Chromosomal mutations = changes the overall structure of a chromosome
Affects multiple genes
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Types of Point Mutations
Substitution = one nucleotide is substituted for another nucleotide
Silent mutation = no change in the amino acid sequence
Missense mutation = one amino acid changes to a different amino acid
Can cause a change in the protein’s final 3-D shape & function
Nonsense mutation = causes a STOP codon to form early
Results in a shorter & usually nonfunctional protein
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Occurs when the wrong base is added to a growing nucleotide chain
Original DNA: TAC GCA TGG AAT
Original mRNA: AUG CGU ACC UUA
Original Protein: Met – Arg – Thr - Leu
Substitution
Original DNA: TAC GTA TGG AAT
Original mRNA: AUG CAU ACC UUA
Original Protein: Met – His – Thr - Leu
Substitution - (Missense)
Silent Mutations
DNA changes that do not cause a change in the amino acid chain
Original DNA: TAC GCA TGG AAT
Mutated DNA: TAC GCC TGG AAT
mRNA: AUG CGG ACC UUA
Protein: Met – Arg – Thr - Leu
Types of Frameshift Mutations
Frameshift mutation = the entire reading frame of the nucleotides shifts
Most amino acids after the mutation will be different
2 types:
Insertion = the addition of nucleotides
Deletion = the deletion of nucleotides
Occurs when an extra base is added to a growing nucleotide chain
Original DNA: TAC GCA TGG AAT
Original mRNA: AUG CGU ACC UUA
Original Protein: Met – Arg – Thr - Leu
Insertion
Original DNA: TAT CGT ATG GAA T
Original mRNA: AUA GCG UAC CUU A
Original Protein: Ile – Ala – Tyr – Leu
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Mutations provide variation among individuals in a population
Evolutionary forces act on these variations
Mutations are useful in research
Allows researchers to modify genes to study their inheritance & molecular functions
Not All Mutations Are Bad