A1. Mutations Flashcards
What are mutations?
(Definition)
Mutations can be caused by errors during ____ ____________. The rate of mutation can be increased by ____________ _______
Any change to the base (nucleotide) sequence of DNA is called a mutation. Mutations can be caused by errors during DNA replication. The rate of mutation can be increased by mutagenic agents
The types of mutations that can occur include:
- Substitution one or more bases are swapped for another, e.g. ATGCCT becomes ATTCCT (G is swapped for T).
- Deletion - one or more bases are removed, e.g. ATGCCT becomes ATCCT (G is removed).
- Addition -one or more bases are added, e.g. ATGCCT becomes ATGACCT (A is added).
- Duplication one or more bases are repeated, e.g. ATGCCT becomes ATGCCCCT (CC is repeated).
- Inversion - a sequence of bases is reversed, e.g. ATGCCT becomes ATCCGT (GCC is reversed to CCG).
- Translocation - 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.
The order of ______ in a ______ determines the ____________ __ _______ ______in a particular ____________. If a ___________occurs in a _____, the sequence of amino acids in the polypeptide that it codes for could be changed.
Polypeptides make up _______. A change in the _______ _____ ______________of a _______________may change the ___________ __________of the protein, which could mean that it _________ ______ ____________.
The order of DNA bases in a gene determines the sequence of amino acids in a particular polypeptide. If a mutation occurs in a gene, the sequence of amino acids in the polypeptide that it codes for could be changed.
Polypeptides make up proteins. A change in the amino acid sequence of a polypeptide may change the tertiary structure (final 3D shape) of the protein, which could mean that it doesn’t work properly.
Example - A mutation in a polypeptide effect on a enzyme
A mutation in a polypeptide that makes up an enzyme may change the shape of the enzyme’s active site. This may stop substrates from being able to bind to the active site, leaving the enzyme unable to catalyse the reaction.
Some mutations can increase the likelihood of developing certain _________, e.g. mutations of the gene BRCA1 can increase the chances of developing breast cancer.
Some mutations can cause genetic disorders - inherited disorders caused by __________ ________ or _______________, e.g. _______ __________.
If a _________(sex cell) containing a mutation for a type of ________or a genetic disorder is ______________, the mutation will be present in the new fetus formed - these are called _____________ ____________because they are passed on to the offspring.
Some mutations can increase the likelihood of developing certain cancers, e.g. mutations of the gene BRCA1 can increase the chances of developing breast cancer.
Some mutations can cause genetic disorders - inherited disorders caused by abnormal genes or chromosomes, e.g. cystic fibrosis.
If a gamete (sex cell) containing a mutation for a type of cancer or a genetic disorder is fertilised, the mutation will be present in the new fetus formed - these are called hereditary mutations because they are passed on to the offspring.
Mutations and proteins
Not all mutations affect the order of amino acids in a protein.
What does the degenerate nature of the genetic code mean?
What is the effect then?
Mutations and proteins
Not all mutations affect the order of amino acids in a protein. The degenerate nature of the genetic code means that some amino acids are coded for by more than one DNA triplet (e.g. tyrosine can be coded for by TAT or TAC in DNA). This means that not all types of mutation will always result in a change to the amino acid sequence of the polypeptide.
Frameshift mutations
Some mutations have a huge effect on the ____ _____________of a gene. Additions, duplications and deletions within a gene will almost always change the _______ _____ _____________of a polypeptide. That’s because these mutations all change the number of _______in the _____ ____. This causes a shift (called a frameshift) in the base triplets that follow, so that?
Frameshift mutations
Some mutations have a huge effect on the base sequence of a gene. Additions, duplications and deletions within a gene will almost always change the amino acid sequence of a polypeptide. That’s because these mutations all change the number of bases in the DNA code. This causes a shift (called a frameshift) in the base triplets that follow, so that the triplet code is read in a different way.
Tip: The base triplets that follow on from the mutation are said
to be ‘____________’ of the mutation.
Tip: The base triplets that follow on from the mutation are said
to be ‘downstream’ of the mutation.
Exam Tip
If you’re asked how a mutation affects protein structure in the exam, don’t fall into the trap of only writing about how the mutation will change the base sequence. Make sure you make it clear how the __________ _____ _____________will affect both the _______ _____ __________ and the __________ ___________.
If you’re asked how a mutation affects protein structure in the exam, don’t fall into the trap of only writing about how the mutation will change the base sequence. Make sure you make it clear how the altered base sequence will affect both the amino acid sequence and the protein’s structure.
