section 1: cellular control - topic 3: gene mutations Flashcards
what is a mutation?
any change to the base (nucleotide) sequence of DNA.
what are the 3 types of mutations?
substitution.
deletion.
insertion.
what is substitution?
one or more bases are swapped for another base.
ATGCCT becomes ATTCCT (G for T)
what is deletion?
one or more bases are removed.
ATGCCT becomes ATCT (GC removed)
what is insertion?
one or more bases are added.
ATGCCT becomes ATGACCT (A added)
what happens if a mutation occurs in a gene?
the order of DNA bases in a gene determines the order of amino acids in a particular protein.
if a mutation occurs in a gene, the primary structure (amino acid chain) of the protein it codes for could be altered.
what may a change in the primary structure cause?
it may change the final 3D shape of the protein so it doesn’t work properly i.e. active sites in enzymes may not form properly, meaning that substrates can’t bind to them.
mutations might also result in a protein not being produced at all.
what is a frameshift mutation?
when an insertion or deletion changes the way the rest of the base sequence is read.
the earlier a frameshift mutation appears in the base sequence…
the more amino acids are affected and the greater the mutations effect on the protein.
why may some mutations have a neutral effect on a proteins function?
the mutation changes a base in a triplet, but the amino acid that the triplet codes for doesn’t change.
^ this happens because some amino acids are coded for by more than one triplet.
the mutation produces a triplet that codes for a different amino acid, but the amino acid is chemically similar to the original so it functions like the original.
the mutated triplet codes for an amino acid not involved with the proteins function.
- if the affected amino acid is located far away from an enzyme’s active site, the protein will work as it normally does.
example of mutations with beneficial effects.
some bacterial enzymes break down certain antibiotics.
mutations in the genes that code for these enzymes could make them work on a wider range of antibiotics.
this is beneficial to the bacteria because antibiotic resistance can help them to survive.
examples of mutations with harmful effects.
cystic fibrosis can be caused by a deletion of 3 bases in the gene that codes for the CFTR protein.
the mutated CFTR protein folds incorrectly, so it’s broken down.
^ this leads to excess mucus production - affects the lungs of CF sufferers.
certain mutations in the BRCA1 gene can increase the risk of developing breast cancer.
BRCA1 produces a protein that helps to repair breaks in DNA.
but mutations in the BRCA1 gene itself can result in a very short protein that can’t do its job.
^ may lead to uncontrolled cell division and the development of cancer.
what can mutations also affect?
whether or not a protein is produced.
i.e. if a mutation occurs at the start of a gene, so the RNA polymerase can’t bind to it and begin transcription, the protein coded for by the gene won’t be made.
example of genetic disorder caused by a mutation.
the HBB gene codes for the beta-globing protein (a component of haemoglobin).
the genetic disorder beta thalassaemia can be caused by a mutation in the region of the HBB gene where transcription is initiated.
a mutation in this region leads to little or no production of beta-globin - leads to low levels of haemoglobin.
^ result - red blood cell development is disrupted and less oxygen can be transported to the body’s cells.
