Lab 2 Flashcards
1
Q
Lecture
Chemical mutagenesis
types of mutations: point mutations
Base changes
A
Base changes
- transitions
- purine to purine or pyr to pyr changes
- Appear most often
- usually 2/3 point mutations are transitions
- less likely to result in an amino acid substitution cuz of 3rd position (wobble)
- transversions
- purine to pyr; or, pyr to purine
- greater chances of changing the encoded amino acid
- change reflects double ring to single ring, or vice versa
- twice as more possible ways it can occur compared to transitions, however, does not occur as often as transitions
2
Q
Lecture
Chemical mutagenesis
types of mutations: point mutations
frame shift
A
- addition or subtraction of a base
- type of mutation involving the insertion or deletion of a nucleotide in which the number of deleted base pairs is not divisible by three
- for any given dna sequence, there are 3 different reading frames, in the 5’ → 3’ per single strand. For a double strand, there’s a total of 6 reading frames.
- any shift, changes the reading frame, and thus the amino acid sequence
3
Q
Lecture
Phenotypic Categories of single base mutations
silent mutation
A
- a change in the sequence of nucleotide bases, without a subsequent change in the amino acid or the function of the overall protein
- doesn’t change codon – neutral substitution
- Sometimes a single amino acid will change, but if it has the same properties as the amino acid it replaced, little to no change will happen
4
Q
Lecture
Phenotypic Categories of single base mutations
missense mutation
A
- point mutation
- changes codon
- a single nucleotide change results in a codon that codes for a different amino acid
- a type of nonsynonymous substitution
- may lead to an appreciable functional change at the protein level
- the amino acid substitution may lead to a neutral change as well
- the first position of the codon is highly relavent in below example
5
Q
Lecture
Phenotypic Categories of single base mutations
nonsense mutation
A
- changes codon to stop codon
- a change in DNA that causes a protein to terminate or end its translation earlier than expected
- a common form of mutation in humans and in other animals that causes a shortened or nonfunctional protein to be expressed
- severity of mutation depends on placement of mutation, i.e., in the beginning, middle, or very end.
6
Q
Lecture
operon
A
- a group of key nucleotide sequences including an operator, a common promoter, and one or more structural genes that are controlled as a unit to produce messenger RNA
7
Q
Lecture
Site of mutations
A
- coding region of structural or regulatory gene
- have substantial effects on phenotypes
- non-coding regions
- less likely to have an effect on phenotypic changes
- Cis-acting effects / polar effects
- mechanisms that affect gene expression only on the same chromosomal allele
- non-coding regions that have a defined function in operon function such as promoters, operators, regulatory binding sites, polar effects, etc
- can have an effect, or eliminate gene expression all together
- polar effects/mutations
- affects expression of downstream genes or operons
- can affect expression of the gene in which it occurs, if it occurs in a transcribed region
- tend to occur early within the sequence of genes and can be nonsense, frameshift, or insertion mutations
- found only in organisms containing polycistronic mRNA
- Regulators (activators, repressors, sigma factors, etc.)
8
Q
Lecture
Results of mutations:
phenotypic consequences
A
- conditional: displayed under one condition (restrictive), but not another (permissive)
- e.g. heat sensitivity, different temps give different phenotypes
- lethal: renders non viable
- leaky mutation: residual activity (partial function)
- eg:
- AA change that affects activity, but doesn’t nullify it
- truncated protein (e.g., change to stop that doesn’t render protein nonfunctional)
- eg:
