Chapter 18: Gene Mutations and DNA Repair Flashcards
What are the two forms of mutations?
Somatic mutations: occur in somatic cells, wont be transmitted to progeny
Germinal mutations: occur in germ-line cells and will be transmitted to progeny
What are the base substitution mutations?
Single nucleotide change
Transition: Pyrimidine with another pyrimidine or purine for another purien
Transversion: Pyrimidine for purine or purine for pyrimidine
What are purines and pyrimidines?
purines: A,G
pyrimidines: T,C,U
What is a frameshift mutation?
insertions or deletions of one or two base pairs alter the reading frame
What is a tautomeric shift mutation?
Movement of H atoms from one position in a purine or pyrimidine base to another, can generate rare A:C and G:T base pairs
What is an expanding nucleotide repeat mutation?
expansion of the triplet repeats, loops are formed between bases that are complementary and then extra nucleotides are added because it cant recognize the loop
What is the pattern of expanding nucleotide repeats and the severity of the mutation?
The greater the number of repeats, the earlier the onset of the disease
What are the 10 effects of mutations?
- forward - wt-> mutant
- reverse - mutant->wt
- missense - amino acid -> different amino acid
- nonsense - sense codon -> nonsense codon (stop)
- silent - codon -> synonymous codon (no change in aa but diff codon)
- neutral - amino acid change with no observable change in protein function
- loss of function mutation - cause complete/partial loss of protein function
- gain of function mutation - causes cell to produce protein whos function is not normally present
- coniditonal mutation - expressed under certain conditions
- lethal - causes death
What is a suppressor mutation?
second site mutation that hides or suppresses the effect of the first mutation (can be within the same gene or on different genes)
Are mutations rare?
YES
What are spontaneous vs induced mutations?
Spontaneous - occur from internal factors
Induced - occur from exposure to external factors
Which mutation is more common, spontaneous or induced?
spontaneous
What are the 5 spontaneous replication errors?
- tautomeric shifts
- mispairing due to other structures - arise through wobble effect or by protonated forms of certain bases
- incorporated errors and replicated errors
- causes of deletions and insertions
- spontaneous chemical changes
What is incorporated error and replicated errors?
can be caused by a tautomeric shift or by the wobble effect or wobble could replicate again to create normal base pairing except opposite (e.g. go from A:T to C:G)
What are the causes of deletions and insertions?
strand slippage - one base loops out and extra is copied creating insertion or deletion
unequal crossing over during meiosis - one crossing over product contains insertion and the other a deletion
What is depurination?
breakage of the covalent bond between the purine base and the 1’ carbon atom of the deoxyribose sugar, so random nt is added, usually an A
What is deamination?
loss of an amino group, typically from cytosine, gives rise to uracil (End results is a C->T)
What are the 7 classes of mutagens?
- Base analogs
- Alkylating Agents
- Deaminating chemicals
- Hydroxylamine
- Oxidative Radicals
- Intercalating Agents
- Radiation
What are Base analogs?
mutagen that are chemicals with structures similar to any of the 4 standard nucleotides and can cause a mispair
What are alkylating agents?
mutagens that react with dna bases and add methyl or ethyl groups
What is hydroxylamine?
mutagen that adds a hydroxyl group to cytosine (C->T)
What are deaminating chemicals?
mutagen that creates addition to spontaneous deamination noted for spontaneous chemical changes
What are oxidative radicals?
mutagens that are reactive forms of oxygen, can create new chemicals which can mispair with the wrong complementary base
What are intercalating agents?
mutagens that sandwich themselves between adjacent base pairs and distorts the helix, they can cause insertions and deletions
