mutations natural and artificial mutations. mutations there are 2 classes of mutations nucleotide...
TRANSCRIPT
Mutations
Natural and Artificial Mutations
Mutations
There are 2 classes of mutations Nucleotide mutations occur when 1-4
nucleotides are altered, added or removed as a result of damage or errors in replication
Transpositions occur when entire sections of DNA “jump” to a different location in the DNA, disrupting genes
Examples of nucleotide mutations Point Mutations – one nucleotide is altered Silent Mutation: CTC to CTT – no change since both
codons code for glutamic acid Missense Mutation: CTC to CTA replaces glutamic
acid with aspartic acid in hemoglobin since they are functionally similar amino acids, the
protein is not greatly affected and the mutation introduces a variation in the species
CTC to CAC replaces glutamic acid with valine Valine is hydrophobic and results in clumping of
hemoglobin, resulting in sickle cell anemia
Sickle Cell Anemia
Nucleotide Mutations
A point mutation could also result in the production of a stop codon in the middle of a gene
If this occurs in an essential protein, such as hemoglobin, the mutation is lethal and is called a nonsense mutation
Frameshift mutations are also normally lethal – the insertion or deletion of a nucleotide shifts the entire reading frame and every codon is altered
Transposons
Transposons
Transposons
Approximately 50 % of the human genome is made up of transposons
They can “jump” from one location to another, or they can copy themselves first, and the copy jumps
Transposons can cause mutations by inserting themselves into exons, or by taking exons with them; “shuffling” the genetic deck
Transposons can jump to a promoter region and either turn off or turn up transcription
Transposons
Artificial Mutation
UV Radiation
UV radiation produces covalent bonds between adjacent thymine base pairs
These dimers block replication by DNA polymerase Cells can repair the damage by removing the
damaged section on one side of the helix DNA polymerase and DNA ligase complete the
repair If the repair is done incorrectly, a mutation results
http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter11/animation_quiz_5.html
Chemical Mutagens
Base analogs Chemicals that have a
very similar structure to thymine, uracil, adenine, cytosine or guanine
Example: 5’bromouracil Base analogs generally
result in point mutations
Chemical Mutagens
Acridine dyes These chemicals have
a positive charge so they bind to the negatively charged DNA
They insert between base pairs and cause frameshift mutations
Examples; nitrous acid and hydrazine
Chemical Mutagens
Alkylating agents Can transfer methyl groups,
ethyl groups, bond with phosphate groups
This can result in any type of mutation, including the lethal breakage of the DNA sugar-phosphate backbone
They are actually used as chemotherapy in the treatment of cancer, destroying the cancerous cells’ DNA
Image from Science Daily