Mutations

DNA mutation

Changes in the DNA nucleotide sequence

DNA mutation = BAD

Causes it to misfunction

Example: a redundant codon makes the same amino acid causing not change in the protein

DNA mutation = good

Cause it to be more efficient

Example: changing the shape of the protein causes the antibiotic to no longer bind to the bacteria causing antibiotic resistance

DNA mutation = neutral

No change in function

Base substitutions

Single base replace w/ a different base in DNA

Effects: vary depending on what change does to the resulting protein

Silent mutations

Mutation still codes for the same amino acid

Effect: no effect due to genetic code redundancy

Missense mutation

Mutation changes codon to code for a different amino acid

Effect: whether it is consequential depends on the protein. If the chemical properties change, it’s not conserved and will have an effect

Nonsense mutation

Mutation changes amino acid to a stop codon

Effect: can drastically shorten proteins. The earlier on in the protein, the greater the problem

Frameshift mutation

Mutation shifts readily frame

Effect: alters the whole protein sequence

Mutation effects on proteins

Enzymatic failure

• changing binding affinity = not able to bind

• Catalytic efficiency = no longer able to catalyze

• Antibiotic resistance

• Porin loss leading to nonfunctional proteins and decreased permeability

• Denaturing proteins at temperatures that they would normally function in

• Altered specificity

Spontaneous mutations

Accidental mistakes when DNA replicates that are not corrected

Mutation is then passed on to offspring

Environmental exposures

Ultraviolet radiation

Exposure to chemical mutagens

Ultraviolet radiation

Results in thymine dimer

Thymine dimer

2 thymine bind together

Becomes problem or when they replicate

Dimer acts like a speed bump

When it hits the dimer it causes an insertion or deletion → frame shift

Mutagens

Agents that directly or indirectly bring about mutations

Nitrous acid

HNO2

Alters the shape of adenine nucleotide resulting in it binding to C rather than T

When helicase unzips and DNA polymerase synthesizes it causes a base pair mutation

Results depend on where it occurs in the protein

Intercalating agents

Mutagen that inserts itself into DNA structure

Can slip between stacked base pairs of the DNA double helix and cause bulges or gaps

Can cause insertions or deletions

Causes from shift could lead to: silent, nonsense, or missense mutations

Example: benzopyren → present in smoke and soot

Mismatch repair

Specific enzymes remove and replace incorrectly paired nucleotides

Nuclease

Enzyme that cuts DNA

Cuts out damaged portion of DNA then DNA polymerase repairs it

Ligase then seals the gaps in DNA

DNA resynthesizes the correct nucleotides