WEEK 12 (Gene mutation, DNA repair and transposition) Flashcards
Single nucleotide substitutions are repaired by which DNA enzymes?
DNA polymerase & DNA Ligase
What are the two types of single nucleotide (point) mutations?
Transition & Transversion mutations
What is the difference between Transition and Transversion mutations?
Transition mutations involve PURINE TO PURINE substitutions or PYRIMIDINE TO PYRIMIDINE
Transversion mutations involve PURINE TO PYRIMIDINE or PYRIMIDINE TO PURINE
List three types of single nucleotide substitutions
- Silent mutation
- Missense mutation
- Nonsense mutation
What is a silent mutation?
A silent mutation codes for the same amino acid & often involves the 3rd position of the codon
What is a missense mutation?
A missense mutation results in a changed amino acid (called CONSERVATIVE if new amino acid has similar chemical structure)
What is a nonsense mutation?
A nonsense mutation results in an early STOP codon (UGA, UAA, UAG) & usually generates a nonfunctional protein
What are the three stop codons?
UGA, UAA & UAG
What is the start codon?
Methionine
What is a Frameshift mutation?
Deletion or insertion of any number of nucleotides not divisible by 3 resulting in the misreading of all nucleotides downstream. Protein may be shorter or longer and its function may be disrupted or altered.
What is a Splice site mutation?
Retained intron remains in mRNA resulting in proteins with impaired or altered function
What is a loss-of-function mutation?
A mutation that reduces or eliminates the function of the gene product
Define Null mutations
Mutations that result in complete loss of function
What is a recessive mutation?
Results in a wild-type phenotype when present in a diploid organism and the other allele is wild type
What is a dominant mutation?
Results in a mutant phenotype in a diploid organism, even when the wild-type allele is also present
What happens in a Dominant negative mutation?
One allele may encode a gene product that is inactive and directly interferes with the function of the product of the wild-type allele
What is a Gain-of-function mutation?
Codes for a gene product with enhanced, negative or new functions
What is a suppressor mutation?
A second mutation that either reverts or relieves the effects of a previous mutation. A suppressor mutation can occur within the same gene that suffered the first mutation (INTRAGENIC MUTATION) or elsewhere in the genome (INTERGENIC MUTATION).
What is a nucleosome?
A repeating unit of chromatin
Histone proteins usually have a high proportion of ____________ amino acids
positively charged
The probability of a particular type of mutation per unit time is known as ____________________
Mutation rate
