3.8 - 3.8.1 Alteration of the sequence of bases in DNA can alter the structure of proteins (A-level only) Flashcards
What are mutations?
Mutations are changes to the base (nucleotide) sequence of DNA.
What can mutations be caused by?
Errors during DNA replication.
What can the rate of mutation be increased by?
Mutagenic agents.
What are the 6 types of mutations which can occur?
Substitution, Deletion, Addition, Duplication, Inversion and Translocation.
What is a Substitution mutation? + example
When one or more bases are swapped for another.
E.g. ATGCCT becomes ATTCCT.
What is a Deletion mutation? + example
When one or more bases are removed.
E.g. ATGCCT becomes ATCCT.
What is an Addition mutation? + example
When one or more bases are added.
E.g. ATGCCT becomes ATGACCT.
What is a Duplication mutation? + example
When one or more bases are repeated.
E.g. ATGCCT becomes ATGCCCCT.
What is an Inversion mutation? + example
When a sequence of bases is reversed.
E.g. ATGCCT becomes ACCGTT.
What is a Translocation mutation? + example
When a sequence of bases is moved from one location in the genome to another. This could be movement within the same chromosome or movement to a different chromosome.
What does the order of DNA bases in a gene determine?
The sequence of amino acids in a particular polypeptide.
If a mutation occurs in a gene, what would happen to the sequence of amino acids in the polypeptide that it codes for?
The sequence of amino acids in the polypeptide that it codes for could be changed.
What do polypeptides make up?
Proteins.
What may a change in the amino acid sequence of a polypeptide change? What could this mean?
The tertiary structure of the protein, which could mean that it does not work properly.
What disorders can some mutations cause?
Genetic.
Inherited disorders caused by abnormal genes or chromosomes, e.g. cystic fibrosis.
Some mutations can increase the likelihood of developing certain cancers.
If a gamete (sex cell) containing a mutation for a genetic disorder or type of cancer is fertilised, the mutation will be present in the new foetus formed. What are these mutations called?
Hereditary mutations because they are passed on to the offspring.
Not all hereditary mutations are harmful. Beneficial hereditary mutations drive what?
Evolution.
True or false?
Not all mutations affect the order of amino acids.
True.
Why do not all mutations affect the order of amino acids? + example
The genetic code is degenerate. This means that some amino acids are coded for by more than one DNA triplet. Therefore, not all types of mutation will always result in a change to the amino acid sequence of the polypeptide.
E.g. some substitutions will still code for the same amino acid. Sometimes, inversion mutations don’t cause a change in the amino acid sequence either.
If a mutation does not cause a change in the amino acid order, what is it called?
A silent mutation.
Additions, duplication and deletions within a gene will almost always change the amino acid sequence of a polypeptide. Why?
That’s because these mutations all change the number of bases in the DNA code. This causes a shift (frameshift) in the base triplets that follow, so that the triplet code is read in a different way.
The base triplets that follow on from the mutation are said to be ‘downstream’ of the mutation.
Mutations occur …
(clue - starts with S)
Spontaneously.
What are some examples of mutagenic agents?
Ultraviolet radiation, ionising radiation, some chemicals and some viruses.
How do mutagenic agents such as ultraviolet radiation, ionising radiation, some chemicals and some viruses increase the rate of mutations?
(clue - 3 ways)
1) Acting as a base - Chemicals called base analogs can substitute for a base during DNA replication, changing the base sequence in the new DNA.
2) Altering bases - Some chemicals can delete or alter bases.
3) Changing the structure of DNA - Some types of radiation can change the structure of DNA, which causes problems during DNA replication.
