6.7 Point Mutations

Mutations

Random changes in the DNA sequences

• can have variable effects on an organism - depends on type and severity

• Most mutations have NO EFFECT on organisms

mRNA Reading Frame

the sequences of nucleotides that are actually read and make for protein

• does not begin w/o AUG

• Does not stop w/o Stop

If mutated, protein structure changes, and protein function may be prevented

Point Mutation

• A mutation of just 1-3 nucleotides

• Affects only 1 gene

Occurs during DNA Synthesis and Cell Cycle

Possible results of mutation

• changes to mRNA sequence

• Changes to amino acid sequence

• Stop protein function

  • Because change shape - nucleotides have different sizes - replacing one ruins structure

• Change phenotype

• Disease

Chromosomal Mutations

• Mutations that affect big sections of chromosomes

• Affect many genes

Occur during meiosis (so only affects sex cells/gametes)

DNA Polymerase

Checks amino acid sequence for any mistakes

• does this during S phase

Substitution Mutation

A type of point mutation where the original nucleotide is replaced by a different nucleotide

• silent

• Missense

• Nonsense

Silent Substitution

Change that codes for the same amino acid as before change

Missense Substitution

Change in a single amino acid in the sequence

• variable effect on protein function and phenotype

• If changes amino acid to have opposite water attraction - change folding

Types:

• Stop protein function

• Decrease functionality

• Increase/form new function

Nonsense Mutation

a change in a single nucleotide that results in a premature stop codon in the mRNA sequence

• afterward codons will not be translated

• Protein will not have all of its amino acids — loss of function

• Depending on where it occurs, protein may lose many A. Acids

• Shortened sequence = A TRUNKATED sequence

Deletion Mutation

Deleting a single nucleotide in the DNA sequence

• changes the reading frame

• changes entire afterward amino acid sequence

• Protein will not fold or function properly

Genetic Variation - Mutations

• can increase genetic variation in a population

• Causes change in protein

• Alter phenotype

• Change in allele frequency

• Causes evolution

Insertion

The addition of a nucleotide base to a sequence - doesn’t involve the replacing of a nucleotide.