19.1 Mutations and Variations Flashcards
What is a mutation?
A change in the sequence of bases in DNA.
Protein synthesis can be disrupted if the mutation occurs within a gene
Three types of mutations
Substitution- one or more bases are swapped for another base
Deletion- one or more bases are removed
Insertion- one or more bases are added
How can substitution affect protein production?
The substitution of a single nucleotide changes the codon. It is a point mutation as it tend to only affect one point/ that one base thereof only affecting one codon
If the new codon codes for a different amino acid, this will lead to a change in the primary structure of the protein.
The degenerate nature of the genetic code may mean however that the new codon still codes for the same amino acid leading to no change in the protein synthesised.
How can substitution affect protein production?
The substitution of a single nucleotide changes the codon.
If the new codon codes for a different amino acid, this will lead to a change in the primary structure of the protein.
The degenerate nature of the genetic code may mean however that the new codon still codes for the same amino acid leading to now change in the protein synthesised.
How can substitution affect protein production?
The substitution of a single nucleotide changes the codon.
If the new codon codes for a different amino acid, this will lead to a change in the primary structure of the protein.
The degenerate nature of the genetic code may mean however that the new codon still codes for the same amino acid leading to now change in the protein synthesised.
How can substitution affect protein production?
The substitution of a single nucleotide changes the codon.
If the new codon codes for a different amino acid, this will lead to a change in the primary structure of the protein.
The degenerate nature of the genetic code may mean however that the new codon still codes for the same amino acid leading to now change in the protein synthesised.
Describe and explain frameshift mutations
The insertion or deletion of a nucleotide, or nucleotides, leads to a frameshift mutation (changes the way the rest of the base sequence is read).
This changes every successive codon from the point of mutation.
The earlier a frameshift mutation occurs in the age sequence, the more amino acids are affected and the greater the mutation’s effect on the protein.
Frameshift of bases -> different amino acids transcribed -> different protein synthesised
However if multiples of three bases are removed or added the reading frame will not be changed but affects number of amino acids transcribe - this is because multiples of three correspond to full codons
3 effects of mutations
- no effect (neutral/ silent mutations) : no effect on the phenotype of an organism as the normal proteins are still synthesised. (E.g. substitution could have no effect if new codon still codes for same amino acid, due to degenerate nature of the genetic code, or the new codon could code for a different amino acid but the amino acid is chemically similar to the original so it functions like the original amino acid) or the mutates triplet codes for an amino acid not involved with protein’s function (e.g. an amino acid located far away from an enzyme’s active site, the protein will work as it normally does)
- damaging/ harmful effects: the phenotype of an organism is affected in a negative way because the proteins are no longer synthesised or proteins synthesised are non-functional. This can affect essential bodily processes. (E.g. cystic fibrosis is caused by the deletion of three bases in the gene that codes for CFTR, so the mutated CFTR protein fold incorrectly and is broken down, this leads to excess mucus production, which affects the lungs overall)
- Beneficial: advantageous/ useful characteristic
E.g. antibiotic resistance
Mutations that are beneficial to the organism are passed on to future generation by the process of natural selection
Causes of mutations
Mutation can occur spontaneously, often during DNA replication, but the rate of mutation is increased by mutagens.
A mutagen is a chemical, physical, or biological agent which causes mutations
- X-rays and other ionising radiations
- viruses
What are nonsense mutations?
- result in a codon becoming a stop codon instead of coding for an amino acid
- the result is a shortened protein being synthesised which is normally non-functional
What are missense mutations ?
Result in the incorporation of an incorrect amino acid into the primary structure when the protein is synthesised
Conservation mutations (when new amino acid coded for has similar chemical properties to the original amino acid) have less severe effects than non-conservative mutations (when new amino acid coded for has different properties to the original ad is more likely to have an effect on the protein structure)
