Ch.19: Gene mutation, DNA repair, and recombination Flashcards
(36 cards)
What are gene mutations?
molecular changes in the DNA sequence of a gene
What is a transition?
a change of a pyrimidine (C, T) to another pyrimidine (T, C) or a purine (A, G) to another purine (G, A)
What is a transversion?
a change of a pyrimidine (C, T) to a purine (A, G) or a purine (A, G) to a pyrimidine (C, T)
Silent Mutations are?
base substitutions that do not alter the amino acid sequence of the polypeptide due to the degeneracy of the genetic code
Missense mutations are?
base substitutions in which an amino acid change occurs
Nonsense mutations are?
base substitutions that change a normal codon to a stop codon
Frameshift mutations involve?
the addition or deletion of a number of nucleotides that is not divisible by three
What mutations are characterized by their differential ability to survive?
Deleterious mutations: decrease the chances of survival. The most extreme are lethal mutations.
Beneficial mutations: enhance the survival or reproductive success of an organism
What do suppressor mutations do?
reverse the phenotypic effects of another mutation
What does an intragenic suppressor mutant do?
the second mutant site is within the same gene as the first mutation
What does an intergenic suppressor mutant do?
the second mutant site is in a different gene from the first mutation
What are the two types that animal cells are classified as?
Germ-line cells: Cells that give rise to gametes such as eggs and sperm
Somatic cells: All other cells
(slide 17 has a good picture for this)
What does Tonr stand for?
T one resistance
What did the Lederberg bacteriophage T1 tonr experiment prove?
By placing random mutants on plates that contained T1 and one that didn’t, it showed that most cells were killed by T1; this showed that spontaneous mutants could occur that provided selective advantages
What are the 3 types of spontaneous mutations?
- Depurination
- Deamination
- Tautomeric shift
What is Depurination? What mutations does it cause?
the removal of a purine (guanine or adenine) from the DNA forming an apurinic site; depurination of A or G can cause both transition and transversion mutants
What is deamination? What mutations does it cause?
deamination of cytosine is the removal of an amino group from the cytosine base
- Base pairing causes the cytosine to be converted to a thymine which results in a C:G to T:A transition mutation
- deamination of 5-methylcytosine causes a C:G to T:A transition mutation
What is a Tautomeric shift and the common stable forms? What mutations does it cause?
A tautomeric shift is a temporary change in base structure
-Tautomeric shifts cause both T:A to C:G and C:G to T:A transition mutations
- The common, stable form of thymine and guanine is the keto form. Rarely, T and G convert to an enol form
-The common, stable form of adenine and cytosine is the amino form/ Rarely, A and C can convert to an imino form
What does oxidative stress do?
Causes a G:C to T:A transversion mutation to counter transition mutation
What are deamination agents?
replace amino groups
with keto groups (–NH2 to =O) ex. nitrous acid
-can change cytosine to uracil and adenine to hypoxanthine
- modified bases do not pair with the appropriate nucleotides in the daughter strand during DNA replication and mutations occur
-Uracil base pairs with adenine and hypoxanthine base pairs with cytosine
What are alkylating agents? What mutations does it cause?
disrupt the appropriate pairing between nucleotides by alkylating bases within the DNA, ex. nitrogen mustards and ethyl methanesulfonate (EMS); cause both cause both G:C to A:T and T:A to C:G transition mutations
What do deamination agents cause?
both C:G to T:A and A:T to G:C transition mutations
What do intercalating agents cause?
frameshift mutations
What do base analogues cause?
transition mutations
