1.6 Mutations Flashcards
what is a mutation and what can it cause
A mutation is a change in the base sequence of the DNA.
Can lead to alteration or absence of proteins.
New characteristics in descendents.
Mutations can only have an effect if they occur in a coding region of DNA – i.e. a section of DNA that codes for a protein or polypeptide
what are the 3 types of mutations
Base substitutions
Base insertions or deletions
Chromosomal mutations
what is base substutition mutation
This is where one nucleotide is substituted for another – a wrong base is placed into position on the DNA.
The altered base will change a single codon, which may change a single amino acid. (but not always – why?)
The single amino acid change may affect the folding (and hence shape) of the protein, resulting in a faulty or non-functioning protein.
Typically the least harmful of the mutations.
what is base insertions and deletions
This is where one nucleotide is inserted or deleted into the DNA.
May result in a ‘frameshift’. As mRNA is read in a sequence of 3 bases, adding or deleting a base will change the reading frame of the sequence.
This will potentially change every codon on mRNA from the point of insertion/deletion leading to many altered amino acids in the resulting polypeptide chain.
This will alter the folding and hence final shape of the protein produced and the protein will likely be non-functioning.
What causes mutation?
DNA replication is an extraordinary process in terms of the high copying fidelity of DNA polymerase.
DNA polymerase can add upwards of 1000 bases per second and despite this, it makes less than 1 error for every 107 nucleotides added.
With additional correction mechanisms, the overall mutation rate is about 1 error per 109 nucleotides added.
The human genome has 3 x 109 bases.
Thus, for every cell division (in humans), approximately 3 changes (mutations) will occur.
what are the chromosomal mutations during cell division
when part of a chromosome is left out, a deletion occurs.
when part of a chromatid breaks off and attaches to its sister chromatid, an insertion occurs. the result is a duplication of genes on the same chromosome.
when part of a chromosome breaks off and reattaches backwards, an inversion occurs.
when part of one chromosome breaks off and is added to a different chromosome, a translocation occurs.
what are carcinogens
Chemical agents that cause or increase the incidence of cancer
what is mutation rate increased by
Ionising radiation– e.g. UV radiation, X-Rays
Mutagenic chemicals
Viruses
what are:
missense mutation
nonsense mutation
frame shift mutation
Missense Mutation: This occurs when a single nucleotide (DNA building block) is changed, resulting in the substitution of one amino acid for another in a protein. This can have a range of effects, from no noticeable change to severe consequences, depending on how crucial the altered amino acid is to the protein’s function.
Nonsense Mutation: This happens when a nucleotide change converts a codon (a set of three nucleotides) that codes for an amino acid into a stop codon. As a result, the production of the protein is prematurely stopped, often leading to a nonfunctional or incomplete protein.
Frameshift Mutation: This occurs when nucleotides are inserted or deleted from the DNA sequence in numbers that are not multiples of three. Since codons are read in groups of three, this shifts the “reading frame” of the sequence, altering every subsequent amino acid in the protein. Frameshift mutations often lead to significant changes in protein structure and function, usually resulting in a dysfunctional protein.
what are the effects of mutations on somatic cells vs germ cells
Mutations that occur in somatic (body) cells) are confined to the organism in which they occur.
They may be confined to a specific tissue or location.
If a mutation occurs in a germ cell (cells that produce gametes), there is potential for them to be passed on as the entire organism carries the mutation.
what is the difference between karyotype and genome
karyotypes focus on the structure and number of chromosomes, while genomes include all the genetic information at the molecular level
