mutations Flashcards
(19 cards)
not all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide.
Why?
1) DNA is degenerate
- more than one codon can code for the same amino acid
2) mutation may occur in introns
- introns are non coding/dont code for proteins
how can a substitution mutation have a positive effect?
- changes amino acid sequence of protein
- this alters the tertiary structure
- changes active site of enzyme
- may allow active site to catalyse reaction more effectively
what is a point mutation?
mutation involving a single nucleotide
what is a substitution mutation?
- one nucleotide is substituted by a different nucleotide
- it has 3 possible effects on a protein
what are the three ways a substitution mutation can affect a protein?
1) no effect
- because genetic code is degenerate
Or
- because substitution occured in non coding region/occured in introns
2) a different amino acid is coded for
- this alters the order of the amino acid sequence
- this alters the tertiary structue of the protein
- this changes the functioning of the protein
-( in enzymes) this changes the shape of the active site so it is no longer complimentary to the substrate
- active site can no longer bind, no more enzyme substrate complexes can form
3) mutated codon does not code for an amino acid
- instead stop codon created
- this triggers translation to stop, this produces shortened protein
- shortened protein cannot function correctly
give an example of a disease caused by a substiution mutation?
sickle cell anaemia
- caused by substitution in gene for one of the polypeptides forming haemoglobin
- haemoglobin molecules form strands with the red blood cells
- makes the red blood cells less effective at transporting oxygen around the body
what is a deletion mutation
a nucleotide is deleted
what is an insertion mutation?
a nucleotide is inserted
what is the effect of a deletion mutation?
- deletion mutation shifts reading frame by one
- this changes the codon, and every codon that follows
- this changes the amino acids coded for
(this is called a frameshift mutation)
what is the effect of an insertion mutation?
- addition of a nucleotide causes frameshift
- this changes the codon, and every codon that follows
- this changes the amino acids coded for
(this is called a frameshift mutation
can result in non functional protein)
mutations at start of gene vs mutations at end of gene
- frameshift mutation near the end of a gene will affect fewer amino acids than a frameshift mutation near the start
- any frameshift mutation could produce a non functional protein
- this may affect phenotype of organism
what happens when a deletion mutation deletes a whole codon?
this is the same for addition mutations
- one amino acid is deleted from protein
- triplet of nucleotides deleted, so reading frame is not affected
- so effect on protein may be relatively small
what is a duplication mutation?
- one or several nucleotides are duplicated
what is the effect of a SINGLE duplication mutation?
- duplication of nucleotide causes frameshift
- this affects the codon and all following codon
- different codon, so diferent amino acids are coded for
what happens if an entire codon is duplicated?
- whole codon duplicated so does not cause frameshift mutation
- BUT additional amino acid now coded for
- could cause dysfunctional protein
what is an inversion mutation?
- group of nucleotides separate
- reattach in same position, but in reverse order
what is the affect of an inversion mutation?
- any inverted codons are affected
- now codes for different amino acid
- does NOT cause frameshift, because number of nucleotides has not changed
can these mutations also affect chromosomes?
yes these are called chromosomal mutations?
