Ch. 22 Part 2: DNA Mutations and Repair Flashcards
How is genetic stability accomplished?
- Accurate DNA replication system 1/10^6
- DNA repair system when damaged 1/10^8
Define mutation
Any change in genetic material or base sequence of DNA
2 consequences of mutations
Somatic mutations: cell changes (disease/cell death) that mostly affect individual
Germ line mutations: heritable diseases (or stable changes leading to evolution)
Rate of mutation
1 mutation/ 10^9
7x10^9 bp/human genome
7 mutations/cell
100 trillion cells
= A LOT of mutations
Explain the 2 types of mutations
- Small scale: single/few bases change
- i.e. Base substitution (transition vs. transversion), base deletion (frameshift), base insertion
- Large scale: chromosomal mutations
- Translocation, inversion, deletion, nondisjunction
Explain difference between transition and transversion
Both examples of base substitution
Transition: Purine to purine
Transversion: Purine to pyrimidine (vice versa)
How else can you classify base substitutions?
Based on consequence:
- Silent: Don’t induce change in amino acid
- Missense: change amino acid
- Nonsense: Introduce stop codon (UAA, UAG, UGA)
What is a frameshift mutation?
Can be caused by deletion or insertion. Causing misreading of sequence, so entirely new amino acid is given. Not called a frameshift if 3 codons, but can still cause disease (Fragile X, Huntington’s)
What is a translocation mutation?
Large scale; Interchange large segments of DNA
Inversion mutation
Large scale; Flip DNA orientation with respect to chromosome (upside down)
Deletion mutation (large scale)
Loss of important genes, can also be caused by chromosomal rearrangment during meiosis (not always bad)
Nondisjunction mutation
Large scale; pairs of chromosomes fail to separate properly
What are insertion, non-frameshift disease?
Fragile X: CGG repeat (5-54 unaffected, 60-230 carriers, 230-4000 retarded)
Huntington’s disease: CAG repeat (11-30 unaffected, 36-121 chorea, death)
What do intercalating agents do?
Insertion and cause frameshift (introduce new base pair)
Exon skipping
base substitution mutation that causes it to no longer think it’s the end of the exon, so includes exon 1, intron, and exon 2 as ONE WHOLE EXON. Essentially, exon 2 skipped.
What is a mutagen?
Physical agent/chemical reagent that causes mutation