What happens when it goes wrong? Flashcards
What are mutations?
Mutations are randomly derived changes in the nucleotide sequences of the DNA of an organism
What are the two types of mutations?
Somatic mutations and germ line mutations
What are somatic mutations?
Occur in somatic cells and are passed on by mitosis but not to sexually produced offspring
What are germ line mutations?
Occur in germ line cells, the cells that give rise to gametes and passes on mutation on fertilisation
What are the different phenotypic effects of mutations?
Silent mutation; gain or loss of function mutations; conditional mutations
What are silent mutations?
Neutral mutations that have no effect on amino acids
What does the gain or loss of function mutations lead to?
Lead to a protein with new altered function or to a non-functional protein
What are conditional mutations?
They cause phenotypes under restrictive conditions but are not detectable under permissive conditions
What is a benefit of mutations?
Drive evolution in the form of genetic diversity
What are large scale mutations?
Chromosomal mutations
What do chromosomal mutations do?
May change the position or cause a DNA segment to be duplicated or lost
What are small scale mutations?
Point mutations (as a result of the gain, loss or substitution of a single nucleotide)
What can small scale mutations also lead to?
Insertion or deletions of one or a few bases
What are the two types of point mutations?
Transition and transversion
What are transition mutations?
Substitution of a purine by the other purine or of a pyrimidine by the other pyrimidine
What are transversion mutations?
Substitution of a purine by a pyrimidine or vice versa
In regulatory sequences for gene expression, what sort of mutation occurs?
Intron-exon borders (splicing)
Describe silent mutations
They involve a base substitution at the 3rd position of the triplet codon and therefore causes no damage
Describe missense mutations
They involve a base substitution that causes a change in the amino acid codon, which may or may not result in an altered function of the protein encoded by the gene
Describe nonsense mutations
They involve a base substitution that causes a stop codon to form and this results in a shortened protein, which is usually not functional
Describe readthrough mutations
They involve a base substitution that causes a stop codon to be converted into an amino acid codon and this results in a lengthened protein which might or might not be functional
What amino acids are polar but with uncharged R groups due to missense mutations?
Serine, Threonine, Glutamine, Asparagine
What amino acids have positively charged R groups due to missense mutations?
Lysine, Arginine, Histidine
What amino acids have negatively charged R groups due to missense mutations?
Glutamic acid, Aspartic Acid
What amino acids have hydrophobic R groups due to missense mutations?
Isoleucine, Leucine, Methionine, Phenylalaline, Tryptophan, Valine, Alanine, Tyrosine
What are frameshift mutations?
These mutations interfere with the opening reading frame of a protein-coding gene
What are the two ways a mutation can arise?
Spontaneous mutations and induced mutations
How do spontaneous mutations occur?
Occur with no outside influence
How do induced mutations occur?
Occur due to an outside agent
What are the several mechanisms of spontaneous mutations that alter DNA?
Errors in replication by DNA polymerase that causes the wrong base to be inserted; bases can have different structures; chemical reactions may have change bases
Describe the different ways an induced mutation can alter DNA
Base analogs (chemicals can alter base); some chemicals add other groups to bases and are DNA modifiers that cause structural changes to DNA; agents that act indirectly on DNA
What are the deaminating agent of induced mutations?
Nitrous acid
What do alkylating agents of induced mutations do?
They act directly on DNA causing mutations through mispairing or error-prone repair
What are intercalating agents of induced mutations and what do they do?
Flat molecules that can slip between base pairs in the double helix, increasing the distance between adjacent bases, leading to structural distortions in the DNA
What is the physical mutations of induced mutations?
Uv radiation is absorbed by thymine, causing it to form covalent bonds with adjcent thymine which disrupts DNA replication
