Ch 13 Altering the genetic material mutation, DNA repair and Cancer Flashcards
A mutation is best defined as:
a heritable change in the genetic material
Mutations are essential for the long-term continuity of life because the supply the __________ that is the foundation for evolutionary change.
genetic variation
Which of the following are ways that point mutations may alter a gene?
A base pair is removed from a gene.
A nucleotide is added to a gene.
The base sequence within the gene is changed.
Where must a mutation occur if it is to directly affect an amino acid sequence?
The coding region of a structural gene
A heritable change in genetic material is known as a(n)
mutation
True or false: New mutations are much more likely to be harmful than beneficial to the individual.
True
Place the following types of mutations in order from the least effect on polypeptide sequence at the top to the most dramatic effect on polypeptide sequence at the bottom.
silent
missense
nonsense
How do point mutations affect DNA sequences?
by adding or subtracting a single base pair
by substituting one base for another
Consider the following wild-type DNA sequence: 5’-CCAAGGTT-3’. Which of the following mutations is a base substitution?
5’-CCCAGGTT-3’
Mutations in noncoding sequences:
may affect gene expression
A mutation may affect the amino acid sequence of a polypeptide only if it occurs within the
coding sequence of a structural gene.
Mutations outside a gene’s coding sequence can affect gene expression. Which of the following sites, when mutated, would affect transcription?
Promoter
Operator site
consider a germ-line mutation that occurs in a sperm which fertilizes a normal egg to produce a zygote. in the individual that results from this zygote, _________% of the cells will contain the mutation, and _______% of the gametes produced by that individual will carry the mutation
100% and 50%
True or false: Nonsense and frameshift mutations generally result in less dramatic changes to a polypeptide sequence than missense mutations.
False
Somatic mutations are not transmitted to an individual’s offspring because:
they do not occur in the gametes
Mutations that occur in noncoding sequences may affect ___
gene expression
Bacterial colonies can be transferred from a master plate to secondary plates in the same configuration using a transferring agent such as a sterile velvet cloth. This technique is known a
replica plating
A spontaneous point mutation may be caused during DNA replication when the enzyme ___ ____
puts the wrong base in a newly-synthesized strand.
DNA polymerase
How do the effects of germ-line mutations in a parent progress over the lifetime of an offspring receiving that mutation?
All of the cells of the individual’s body, but only half of the gametes produced by that individual will carry the mutation
Induced mutations are caused by:
environmental agents
How do somatic mutations affect an individual’s offspring?
The mutation does not occur in germ line cells and therefore does not affect the offspring
The effects of ___________ mutagens on DNA structure is varied. Some can alkylate bases, others act as base analogues, and a few can insert between bases in the double helix and cause additions or deletions.
chemical
Which of the following are ways that ionizing radiation can alter DNA structure?
- base deletion
- breaks in one or both DNA strands
What is the process in which bacterial colonies are transferred from a master plate to secondary plates in the same configuration using a transferring agent such as a sterile velvet cloth?
Replica plating
What is a thymine dimer?
A site where two adjacent thymine bases become covalently cross-linked to each other
____ are small segments of DNA that can insert at various sites in the genome. If they insert into a gene, they may cause a spontaneous mutation.
Transposons
Mutations can be divided into two main types. Spontaneous mutations result from abnormalities in biological processes while _____ mutations are caused by environmental agents that enter the cell and alter the structure of the DNA
induced
Nitrous acid, nitrogen mustard, 5-bromouracil, and benzo(a)pyrene are examples of ______________ mutagens.
chemical
Which of the following are ways that chemical mutagens covalently modify the structure of nucleotides?
Alkylation of bases
Deamination of bases
X-rays and ultraviolet light are examples of ______ mutagens.
physical
Nonionizing radiation, such as ultraviolet light, can lead to:
the formation of a thymine dimer
The ____________ test, which was developed in the 1970s, is used to evaluate the ability of a substance to cause mutations.
Ames
A ______________ ______________ is a site where two adjacent thymine bases become covalently cross-linked to one another.
thymine and dimer
Which of the following are chemical mutagens?
Nitrous acid
Benzopyrene
Ethyl methanesulfonate
Nitrogen mustard
A compound is subjected to the Ames test to evaluate its ability to cause mutation. If the substance is a mutagen, what results are expected?
There will be more bacterial colonies on the plate exposed to the mutagen than on the control plate.
Which of the following are physical mutagens?
X-rays
UV light
Which of the following organisms have the ability to repair DNA and thus minimize mutations?
all living things
What is the purpose of the Ames test?
Evaluation of the ability of a substance to cause mutation
Organisms possess different types of DNA repair systems. In a type called ____ repair, an enzyme recognizes and removes an alkyl group, thus restoring the base to its original structure.
direct
In nucleotide excision repair, what serves as the template for synthesis of new DNA to replace the damaged strand?
The complementary strand of DNA
Which of the following exhibit nucleotide excision repair (NER)?
Plants
Humans
Mice
Bacteria
In the Ames test, you expose S. typhimurium cells that cannot synthesize histidine to compound X, then plate them on a medium lacking histidine. The next day you observe a higher number of colonies on this plate versus the control plate, which has bacteria with no exposure. What reasonable conclusion can you draw?
Compound X is a mutagen
Arrange the events that occur in nucleotide excision repair in E. coli in the correct order. Start with the earliest step on top.
- the UvrA-UvrB complex identifies a damaged site
- UvrC makes cuts on both sides of the damaged site
- UvrD binds and removed the damaged region
- DNA polymerase synthesizes new DNA to fill the gap
- DNA ligase seals the newly synthesized DNA to the original strand
True or false: All living things possess mechanisms allowing them to minimize mutation.
True
An alkylated base is recognized by an enzyme. The enzyme removes the alkyl group and restores the normal base structure. What type of DNA repair is this?
- A region of several nucleotides in the damaged strand is removed from the sequence
- The undamaged strand is used as a template to synthesize a normal strand
Nucleotide excision repair (NER) is found in:
prokaryotes and eukaryotes
Match each protein involved in nucleotide excision repair in E. coli with its function.
- cuts DNA on both sides of the damaged site
- removed the damaged region
- synthesizes new DNA to fill in the gap
- seals newly synthesized DNA to the original strand
- identifies a damaged site
