Gene Mutations Flashcards
What are the two main classes of DNA mutation?
Point mutation and Insertion/deletion otherwise known as indel mutations.
What is point mutation?
It is when one base pair replaces (is substituted for) another base.
What are indel mutations?
One or more nucleotides are inserted or deleted from a length of DNA.
What are the three types of point mutation?
Silent
Missense
Nonsense
Define silent mutations.
A point mutation involving a change to the base triplet, where that triplet still codes for the same amino acid.
Describe the ‘redundancy’ or ‘degeneracy’ of the genetic code.
There are some triplet bases that code for the same protein. This reduces the affect of point mutations, as they do not always cause a change to the sequence of amino acids in a protein.
Define a missense mutation.
A change to the base triplet sequence that leads to a change in the amino acid sequence in a protein.
Describe what happens as a result of missense mutations.
Within a gene, such a point mutation may have a significant effect on the protein produced. The alteration to the primary structure leads to a change to the tertiary structure of the protein, altering its shape and preventing it from carrying out its usual function.
Give an example of a condition which is a result of missense mutations.
Sickle cell anaemia
What is a nonsense mutation?
When a point mutation alters a base triplet, so that it becomes a termination (stop) triplet.
What does a nonsense mutation result in?
A truncated protein that will not function.
What happens to the truncated protein?
It will be broken down in the cell.
Give an example of a condition which is a result of a nonsense mutation.
The genetic disease Duchenne muscular dystrophy.
What is a frame shift? And what causes them?
A frameshift happens when base pairs ( not in multiples of three) are added or deleted from an amino acid chain. Due to the chain being read in triplet bases it means that all amino acids after that point are then different as the amino acid chain has shifted.
What is affected by a frameshift?
The primary and tertiary structure of the protein. Therefore the protein cannot carry out its normal function.
Give an example of a disorder caused by a frameshift.
Thalasseamia, a haemoglobin disorder.
What are expanding triplet nucleotide repeats?
When a gene which already has repeating amino acids, adds more of the repeated amino acids each time it replicates.
Give an example caused by expanding triplet nucleotide repeats?
Huntington disease.
Give an example of neutral mutations in humans.
Inability to smell certain flowers (honeysuckle and freesias).
Differently shaped ear lobes
What is a neutral mutation?
They are neither harmful nor beneficial.
