Topic 8—A:Mutations and Gene Expression-1. Mutations Flashcards
What are mutations?
- Any change to the base (nucleotide) sequence of DNA
How can mutations be caused?
- By errors during DNA replication
How can the rate of mutations be increased?
- by mutagenic agents
What are the different types of mutations?
- substitution
- deletion
- addition
- duplication
- inversion
- translocation
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
What determines the sequence of amino acids in a particular polypeptide?
- order of DNA bases in a gene
What happens to the sequence of amino acids in the polypeptide if a mutation occurs in a gene?
- they could be changed
What do polypeptides make up?
- proteins
What may change as a result of a change in the amino acid sequence of a polypeptide?
- It may change the tertiary structure (final 3D shape) of the protein which could mean that it doesn’t work properly
E.g.
a mutation in a polypeptide that makes up an enzyme may change the shape of the enzymes active site
This may stop substrates from being able to bind to the active site leaving the enzyme unable to catalyse the reaction
What can some mutations increase the likelihood of?
- developing certain cancers
E.g. mutations of the gene BRCA1 can increase the chances of developing breast cancer
What can some mutations cause?
- genetic disorders
What are genetic disorders?
- inherited disorders caused by abnormal genes or chromosomes
E.g. cystic fibrosis
What will happen to the mutation Of 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 offspring
What does the degenerate nature of the genetic code mean?
- some amino acids are coded for by more than one DNA triplet
- this means that not all types of mutation will always result in a change to the amino acid sequence of the polypeptide
Definition of frame shift mutation
- a mutation that changes the number of bases in the DNA code, causing a shift in the base triplets that follow, so that the triplet code is read in a different way