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Mutations
MUTATIONS
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.
Types of Mutations
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
mRNA: GGGUAAGAA
if
CCCATTCTC
GGGUAAGAG
ii) Missense Mutation
- alters codon causing it to code for a different
amino acid (e.g. cause of sickle cell anemia)
iii) Nonsense Mutation
- alters codon changing it to a STOP codon and
only part of the protein is translated
- lead to non-functional proteins
iv) Base-pair Insertion/Deletions
- 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)
HEY MAN HOW ARE YOU BRO
Compare to:
HEY MAN HWA REY OUB RO_
HEY MAN HOQ WAR EYO UBR O__
Chromosomal Mutations: - involve large segments of
DNA
Duplication
Translocation
Inversion
ABCDEFG

ABEDCFG
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