(Chap 13) Mutations Flashcards
3 types of DNA mutations
Substitution
Deletion
Insertion
2 types of Frame shift
Deletion
Insertion
Describe the mutation called an “in-frame deletion or insertion”
It is the deletion or insertion of a multiple of three nucleotides that doesn’t alter the reading frame.
What is a tranversion?
The replacement of a Purine to a Pyrimidine or the inverse.
Base substitutions can be ___________ or _____________.
Transitions or transversion.
Transitions - A to G or G to A/T to C or C to T
Transversions - A to C, A to T, G to C, G to T/C to A, C to G, T to A, or T to G
What is a transition?
The replacement of a Purine to another Purine or a Pyrimidine to a Pyrimidine
What is a suppressor mutation?
It occurs elsewhere within the same gene, or in another gene altogether, but restores the wild-type phenotype.
DNA mutations are genetic, but not always ___________.
heritable
What is a germ-line mutation?
These are mutations that arise in cells that ultimately produce gametes and can be passed to future generations.
What type of suppressor mutation occurs in the SAME gene as that containing that mutation being suppressed?
Intragenic suppressor mutation
Intragenic suppressor mutation
Type of suppressor mutation occurs in the same gene as that containing that mutation being suppressed but it restores the wild type with different genotype.
Intergenic suppressor
A mutation in a different gene (eg. tRNA) can suppress mutation that are copied into mRNAs.
Epistasis.
Types of substitution mutations
1) Silent (change of a nucleotide without change in amino acid sequence)
2) Neutral (change of one a.a. but it doesn’t affects the function of the final product)
3) Missense (when the change of a single base pair causes the substitution of a different amino acid in the resulting protein affecting the function of the final product)
Silent mutation
Change of a nucleotide in the codon (e.g. 3rd nucleotide wobble) without change in amino acid sequence
Neutral mutation
Change of one amino acid but it doesn’t affects the function of the final product
Missense mutation
When the change of a single base pair causes the substitution of a different amino acid in the resulting protein affecting the function of the final product
Nonsense Mutation
A change in a sense codon (deletion or insertion) leads to a premature termination of translation.
Forward Mutation (1st mutation)
Changes of the wild phenotype to a mutant phenotype
Reverse Mutation (2nd mutation)
Corrects the exact original mutation. Changes of the mutant phenotype back to the wild phenotype.
Suppressor mutation
Occurs elsewhere within the same gene, or in another gene, but restores the wild-type phenotype. The genotype is different from the wild-type.
What are tautomeric shifts and its possible effect of DNA?
It is a proton shift which rearranges the double bond of a base. This normally occurs but only for a fraction of a second. The shift can lead to a spontaneous mismatch of base pairs.
Why is spontaneous mutation rate low?
Fidelity of the replication enzymes and the efficiency of the DNA repair systems.
What is tautomeric shifts?
a bond shift in the ring structure of a nitrogenous base
What type of mutation results from unequal crossing over?
spontaneous mutation
What are base analogs?
chemical mutagens that can be incorporated into DNA, and then proceed to base-pair incorrectly, which introduces mutations into the DNA.
What type of mutation results from chemical mutagens?
induced mutations
Which bases are pyrimidines?
cytosine, thymine, and uracil
UV light creates ___________ ______________ which __________ _____ _______________
Pyrimidine dimers bend the DNA backbone
What is the Ames test?I
t is a method used to determine how mutagenic a substance may be.
Ames test protocol
1) His(-) in minimun media,
2) Compound X (the substance being tested that will mutate His (-) to His (+)
3) Liver enzymes to know if liver when reacts with Compound X produces the reversion to His (+)
4) High levels of His (+) means compound X is mutagenic
What are transposons?
are mobile DNA segments that can disrupt gene function by inserting in or near genes.
What rare genetic disease is characterized by acute sensitivity to sunlight and a predisposition to skin cancer?
Xeroderma pigmentosum
What is the mismatch repair system?
A type of excision repair that specifically repairs mismatches that occur due to Pol error during replication, the newly synthesized strand can be targeted due to under methylation.
1) What enzyme removes methyl groups from bases such as in Guanine?
2) In what type of repair system is used?
1) methyltransferase
2) direct repair
What is a direct repair system?
changes the affected nucleotide back to its original structure
1) What enzyme adds methyl groups from bases such as in Cytosine?
DNMT1 (DNA (cytosine-5)-methyltransferase 1)
What rare genetic disease is characterized by defects in nucleotide-excision repair?
Xeroderma Pigmentosa
What is the problem in Xerodema pigmentosa
defects in nucleotide-excision repair
