mutation Flashcards
(44 cards)
Mutation
The alteration of a sequence of nucleotides in DNA, that may change the RNA product.
Carcinogenic mutagens
Mutagens that change the cell cycle, causing increased cell division with no differentiation and creating masses of cells known as tumours.
What mutations cause cancer?
Mutations in proto-oncogenes and tumour suppressor genes.
Electromagnetic radiation sources
Enter cells from external sources and interfere with DNA molecules in the nucleus due to its highly-penetrative high-energy waves.
Ex. gamma rays, x-rays and UV light
Pyrimidine dimers
UV creates a dimer structure by causing two adjacent base pairs to form covalent bonds with each other.
Why are pyrimidine dimers bad?
They distort DNA’s double helix structure and prevent T bases form bonding with the opposite A bases.
The dimer structure isn’t replicated by DNA polymerase so no nucleotides are paired with the covalent pair, altering the mRNA sequence and negatively affecting protein structure/protein function.
How else may radiation indirectly damage DNA?
By ionising other molecules to produce highly-reactive free radicals.
These unpaired electrons want to strip electrons from any molecules they encounter, reacting with DNA to damage it.
Examples of chemical mutagens
Ingested chemicals like alcohol, charred and fatty foods. Environmental irritants and poisons like asbestos and pesticides.
Base analogues
Chemicals structured similar to normal bases in DNA and may mistakenly become incorporated into DNA during replication. Results in mispairing of nucleotides, creating a non-functional protein product.
Intercalating agents
Chemicals that insert themselves into the bonds between DNA pairs, altering the shape of DNA. Causes errors in replication.
Reactive oxygen species
Chemicals that react directly with DNA and can cause breakages and cross-links in DNA strands.
Naturally occurring mutagens
Spontaneous mutations like DNA replication errors that are retained because normal DNA repair doesn’t correct them
Non biological naturally occurring mutagens
Metals like mercury and cadmium that occur naturally in the environment
Biological naturally occurring mutagens
Viruses, bacteria, fungi and their products.
Mutagenic microbes can insert their own base sequence into DNA, changing the functioning of genes and triggering cancer.
Transposons
Sections of DNA that spontaneously fragment and relocate or multiply within the genome.
When inserted into chromosomal DNA, they disrupt DNA functioning.
Microbes
Mutagens such as viruses (HIV, hep B) and bacteria (Helicobacter) that may alter the genetic material in cells.
Point mutation
A single nucleotide variation. Different from SNPs because they exist in less than 1% of the species’ population.
Effects of point mutation
Affects phenotype if they occur within the exon of a gene, or affects gene expression when occurring within an intron.
Base substitution
When one nucleotide base is replaces by a different base, possibly leading to a different amino acid inserted in the polypeptide.
Nonsense mutation
Amino acid is changed into a premature stop codon, resulting in a non-functional resulting protein that has major phenotypic effect.
Missense mutation
Results in an amino acid change. Functionality of the resulting protein is determined by whether the replacement amino acid is the same as the original.
Silent mutation
When a substitution results in a new codon that still codes for the same amino acid, and thus have no effect on proteins and phenotype. Doesn’t alter amino acid sequence.
Neutral mutation
Changes in DNA that result in an amino acid of the same type as the original so the change doesn’t significantly affect the structure of the protein.
Sickle cell anaemia
A missense mutation; the amino acid glutamate is swapped for valine, altering the shape of the haemoglobin molecule and resulting in the sickle cell shape of the red blood cells.
