What does a change in the amino acid primary sequence of a polypeptide result in?
- Change is shape and function of the protein
What can a change in the genetic base sequence result in?
- Different amino acids being coded for
What types of mutational changes are there?
- Point mutations
- Insertions/deletions
What are point mutations?
- Base substitutions
- Also called Single Nucleotide Polymorphisms (SNPs)
What types of point mutations are there?
- Transition: Purine to purine, Pyrimidine to pyrimidine (more common)
- Transversion: purine to Pyrimidine, pyrimidine to purine
What types of point mutations are there that occur in coding regions of a protein?
- Silent mutation
- Missense mutation
- Nonsense mutation
Can point mutations in non-coding regions or outside genes have a detrimental effect?
- Yes
- Can alter binding sites, promoter sequence, splice sites
What type of mutations can insertions/deletions cause?
- Frameshift mutations
What is an insertion or deletion mutation?
- A sequence is added or removed from the nucleic acid
- It can be a single nucleotide (single base mutation), a few nucleotides (eg triplet repeats) or millions of nucleotides (eg tandem duplications)
What is a silent mutation?
- A point mutation that occurs in a coding region
- Does not alter the amino acid specified
- Most usually a single-base change at the third codon position
What is a missense mutation?
- Occurs in a point mutation in a coding region
- A mutation that replaces one amino acid with another
What is a nonsense mutation?
- A type of point mutation in a coding region
- Mutation changes an amino acid to a stop codon
What is a frameshift mutation?
- Caused by an insertion/deletion
- Addition or subtraction if nucleotides not in multiple of three
- Causes all subsequent triplet codes to shift causing the amino acids to change
- Stop codons are commonly found in alternative reading frames and cause termination of translation prematurely (premature termination codon (PTC)
How do mutations occur? What are the the 2 main types?
- Spontaneous mutations
- Induced mutations
How do spontaneous mutations occur?
- Not caused by exposure to a known mutagen
- Caused by errors in DNA replication as DNA bases have a slight chemical instability
- Each individual has multiple new mutations and by chance most are not in the coding regions
What does the differing rate of spontaneous mutations for different genes depend on?
- Size
- Sequence
What are induced mutations?
- Chemicals and radiation can cause mutations
- Chemicals that cause a mutation are called mutagens (are mutagenic)
- Chemicals that cause cancer are called carcinogens (are carcinogenic)
What are some examples of mutagens?
- Alkylating agents: remove a base
- Acridine agents: add of remove a base
- X Rays: break chromosomes/delete a few nucleotides
- UV radiation: creates thymidine diners
Define mutation
- A change in a nucleic acid sequence, which can be the addition of one or more (or many) nucleotides [insertion], the removal of one or more (or many) nucleotides [deletions], or the rearrangement of several (or many) nucleotides
Define wild-type
- An individual within a population displaying a wild-type trait, which is the trait that is the most common in that population
What phenotype can a mutation cause?
- Mutant phenotype
- A phenotype that differs from the common or wild type phenotype in the population
What type of allele can a mutation in a gene cause?
- Mutant allele
- Allele that differs from the common or wild type allele in the population
What are mutations that occur in the germline?
- Germline mutations
- Can be passed on to offspring
How often do mutations occur and what is done about them?
- Very frequently
- Are recognised and repaired very frequently too
