Transcript Mutations

Mutations
•
changes in the DNA sequence that can be inherited
•
can have negative effects (a faulty gene for a trans-membrane protein leads to
cystic fibrosis), but most mutations go unnoticed (we have two copies of each
gene).
Type 1: Point Mutations
a)
b)
c)
d)
Silent Mutations - have no effect on cell function (two types)
•
Errors that are located in intron regions - get cut out before translation.
•
Genetic code redundancy - a change in the sequence may not alter the
amino acid (eg. UUU and UUC both result in phenylalanine)
Missense Mutation
•
When a change in the sequence of DNA alters a codon, resulting in a
different amino acid being put in the peptide sequence.
•
Sickle cell anemia occurs because of a missense mutation.
Nonsense Mutation
•
A change in the DNA sequence causes a STOP codon to be inserted in
place of an amino acid codon.
•
The protein produced is truncated (too short).
Frameshift Mutations - causes the reading frame for codons to change.
•
Can result from deletions of nucleotides from the DNA sequence or from
insertions of nucleotides into the sequence.
•
Either way, it shifts the reading frame in translation and results in a
completely different sequence of amino acids being constructed.
•
Note that inserting or deleting 3 bases in the DNA wouldn’t shift the
reading frame, it just adds or removes an amino acid.
Type 2: Chromosomal Mutations
a)
b)
Translocation
•
A segment of DNA moves from one part of the genome to another, usually
non-homologous chromosome.
•
If it ends up in the middle of a gene, it can be transcribed, translated and
form a “fusion protein” as seen in some types of leukemia.
Inversion
•
A segment of DNA reverses its orientation in the chromosome which can
disrupt the gene or affect control of transcription.