Mutations. MUTATIONS. Cells have evolved mechanisms to avoid errors during DNA replication. Strands are “proofread” to ensure accuracy and correct any mistakes.
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Cells have evolved mechanisms to avoid errors during DNA replication. Strands are “proofread” to ensure accuracy and correct any mistakes.
Still, changes in the genetic message (nucleotide sequence of DNA) can occur. Mutations can arise spontaneously or as a result of exposure to mutagens.
2 Categories : point mutations and chromosomal
POINT MUTATIONS – mutations at a specific base pair. Include:
i) Silent Mutation
- has no effect due to occurring in introns of DNA or
redundant nature of genetic code (e.g.
GAA and GAG both code for glutamic acid)
DNA: CCCATTCTT if CCCATTCTC
mRNA: GGGUAAGAA GGGUAAGAG
- alters codon causing it to code for a different
amino acid (e.g. cause of sickle cell anemia)
- alters codon changing it to a STOP codon and
only part of the protein is translated
- lead to non-functional proteins
- when one or more nucleotide pairs are either
inserted or deleted from a gene
- have a greater effect on proteins than substitutions
- can cause frameshift mutations: occurs when
number of nucleotides inserted/deleted is not 3 or a
multiple of 3
- causes nucleotides to be improperly grouped into
codons producing non-functional proteins (unless at
end of gene)
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