Reading Assignment 16
How does ionizing radiation cause mutations?
It forms free radicals that can introduce breaks into the DNA molecule.
5-bromouracil is a base ______ that changes a(n) ______.
analog; AT base pair to a GC base pair
The two main mechanisms used to repair DNA double-strand breaks are ______ recombination repair and _______ end joining.
homologous, nonhomologous
An agent that can change DNA structure and cause mutations is known as a(n)
mutagen
A chemical agent is being assayed for mutagenicity using the Ames test. This agent would be judged to be a mutagen if the number of bacterial colonies on the test plate is ______.
significantly higher than that of the control plate
The strand that is repaired in the mismatch repair system is ______.
the nonmethylated strand
Some errors affect individual nucleotides and do not distort the DNA double helix. These errors are removed primarily by a DNA repair system called BER, which stands for _______________ ______________ repair.
Base excision
Which of the following terms is associated with ionizing energy? Near Ultraviolet light Gamma rays Short wavelength Long wavelength Low energy High energy
Gamma rays Short wavelength High energy
In which of the following ways does 5-bromouracil cause a mutation?
It replaces the base thymine, and can base pair with guanine rather than adenine.
Which of the following statements about DNA N-glycosylase is true?
Living organisms produce many types, each of which deals with specific types of abnormal bases.
If the proofreading ability of a DNA polymerase fails, which of the following DNA repair systems is most likely to detect the resulting mutations and fix them?
Mismatch repair system
Some errors create bulky distortions of the double helix. These errors are removed primarily by a DNA repair system called NER, which stands for ______________ ____________ repair.
Nucleotide excision
The enzyme that can recognize thymine dimers and split them is called _______________
Photolyase
In the Ames test for mutagenicity, the control sample contains what?
Rat liver extract + Salmonella bacteria that cannot synthesize histidine
In the nucleotide excision repair (NER) system, select the complex that recognizes damaged DNA, followed by the proteins that act to remove the damaged DNA.
UvrA/UvrB complex; UvrC (endonuclease) and UvrD (helicase)
Base analogs induce mutations
being incorporated instead of normal bases during DNA replication
Alkylating agents attach ___ or ____ groups to DNA bases and thus disrupt their normal base pairing properties.
methyl or ethyl
During DNA replication, a base that does not obey the normal AT/GC base pairing rule is added. This type of mutation is most likely corrected by ____ the repair system
mismatch
In the mismatch repair system, how is the newly-made daughter strand distinguished from the parental strand?
The parental strand is methylated, while the daughter strand is not.
Thymine dimers are typically caused by ______.
UV light
This child has the disease________which makes her more susceptible to skin cancer.
Xeroderma pigmentosum
Which of the following human diseases is associated with a high predisposition to skin cancer because of an inability to repair UV-induced lesions?
Xeroderma pigmentosum
Ionizing radiation produces chemically reactive molecules known as ____________ _______. These are mutagenic because they alter the structure of DNA.
free radicals
Acridine dyes cause ______ mutations.
frameshift
Acridine dyes induce mutations by ______.
inserting themselves between adjacent bases and thus distorting DNA structure
Ultraviolet light causes the formation of crosslinked _______in DNA.
pyrimidine dimers
Ionizing radiation is characterized by ______.
short wavelength and high energy
Certain compounds have a structure similar to normal DNA bases and so can be incorporated into daughter strands during DNA replication. These compounds are called base _____.
Analogs
True or false: During homologous recombination repair, the two broken ends of DNA are pieced back together.
False
Base excision repair (BER) is the main system used in the repair of ______.
abnormal bases
A mutagen is a(n) ______
agent that causes mutations
Nucleotide excision repair (NER) is the main system used in the repair of ______.
bulky, helix distorting lesions
Alkylating agents cause mutations by ______.
disrupting the normal pairing between nucleotides within the DNA
