Chapter 13: Altering the Genetic Material
About ___________-% of human cancers are associated with mutations of the p53 gene.
50
Mutations of the p53 gene are involved in what percentage of human cancers?
50%
Approximately ___________% of cancers may be attributed to carcinogens.
80
What percentage of cancers are related to exposure to carcinogens?
80%
What is an oncogene?
A mutant gene that promotes uncontrolled cell growth
What is a proto-oncogene?
A normal gene that can become an oncogene if it is mutated.
Which of the following statements regarding nucleotide excision repair (NER) are true?
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
The function of a tumor-suppressor gene can be lost in three common ways. Which of the following is NOT one of them?
Abnormal DNA acetylation near the promoter of the gene -- Abnormal DNA methylation near the promoter can inactivate the gene
What are somatic cells?
All cells of the body that are not germ line cells
What is gene amplification?
An increase in the number of copies of a gene
What is a tumor?
An overgrowth of cells
Which of the following exhibit nucleotide excision repair (NER)?
Bacteria Humans Plants Mice
Why does the inherited type of retinoblastoma typically occur early in life?
Because only one new mutation is required
How can a missense mutation in a proto-oncogene cause cancer?
By altering the function of the encoded protein
How can a chromosomal translocation cause cancer?
By creating an abnormal gene that encodes a fusion protein
How can gene amplification of a proto-oncogene cause cancer?
By generating too much of the encoded protein
Why does cancer affect people more as they age?
Cancer involves a series of mutations that take time to accumulate in a cell lineage.
What type of genetic change promotes cancer by causing the production of an abnormal fusion protein?
Chromosomal translocation
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
The p53 protein is encoded by a tumor-suppressor gene which is expressed when ___________ is damaged.
DNA
The p53 protein is encoded by a tumor-suppressor gene which is expressed when ____________ is damaged.
DNA
The expression of the p53 gene is induced in response to:
DNA damage
Xeroderma pigmentosum is a genetic disease that affects:
DNA repair
Which of the following are ways that chemical mutagens covalently modify the structure of nucleotides?
Deamination of bases Alkylation of bases
Which of the following DNA repair systems can detect and correct damaged or altered DNA bases?
Direct repair Nucleotide excision repair Base excision repair
What protein is inhibited by the Rb protein?
E2F
True or false: Retinoblastoma is an adult cancer which is only caused by exposure to environmental agents later in life.
False
True or false: Cancer usually requires only one or two genetic changes to the same cell lineage.
False -- cancer usually requires around 10 or more genetic changes to the same cell lineage.
In which phases of the cell cycle are the three checkpoints located?
G1 G2 Metaphase
In response to DNA damage, p53 will arrest the cell cycle at:
G1 checkpoint
The three checkpoints that will stop the cell cycle if genetic abnormalities are detected are found in the following phases: ____________, ____________, and ____________.
G1, G2, metaphase
The Ras protein is active when it is bound to:
GTP
How does the Ras protein return to an inactive state?
It hydrolyzes GTP to GDP.
What is the function of the Rb protein?
It inhibits cell division.
What is the function of the p53 protein?
It is a transcription factor.
Which of the following best describes the retinoblastoma (Rb) gene?
It is a tumor-suppressor gene involved in the negative regulation of cell division.
Why is liver extract used in the Ames test?
Liver enzymes may be needed to convert a chemical into a mutagen
Which of the following steps occurs last during cancer progression?
Metastasis
Which of the following types of DNA damage can be fixed using nucleotide excision repair (NER)?
Missing bases Thymine dimers Chemically-modified bases
What statement about carcinogens is true?
Most of them are also mutagenic.
What are the three most common ways that the function of a tumor-suppressor gene is lost?
Mutation within the gene Abnormal DNA methylation near the gene's promoter Loss of the chromosome that carries the gene
Which DNA repair system can correct a variety of types of DNA damage, including thymine dimers, missing bases, and chemically modified bases?
Nucleotide excision repair
Which of the following statements about retinoblastoma is correct?
Retinoblastoma may be caused by inherited mutations or by environmental agents.
What organism is used in the Ames test?
Salmonella typhimurium
What missense mutation is least likely to affect protein function?
Substitution of a positively charged amino acid for another positively charged amino acid
In nucleotide excision repair, what serves as the template for synthesis of new DNA to replace the damaged strand?
The complementary strand of DNA
How does the protein encoded by the ras oncogene differ from the protein encoded by the normal ras gene?
The protein encoded by the oncogene is unable to hydrolyze GTP.
What does a gene mutation affect?
The sequence of bases in a particular gene
What is metastasis?
The spread of cancerous cells through the bloodstream or body fluids
How do growth factors promote cell division?
They activate pathways that trigger gene transcription.
How does xeroderma pigmentosum (XP) affect individuals that have inherited this disorder?
They are highly sensitive to the sun.
What are the typical functions of proteins encoded by genes that may become oncogenes?
Transcription factor Growth factor receptor Intracellular signaling protein
Which of the following terms describes the movement of a DNA segment from one chromosome to another?
Translocation
True or false: All living things possess mechanisms allowing them to minimize mutation.
True
Which of the following genes encode proteins that help prevent cancer?
Tumor-suppressor genes
Which of the following are physical mutagens?
UV light X-rays
The four proteins involved in nucleotide excision repair in E. coli are called
UvrA, UvrB, UvrC, UvrD
In E. coli, the four key proteins comprising the nucleotide excision repair (NER) system are called:
UvrA, UvrB, UvrC, and UvrD
Which of the following genetic diseases affect DNA repair systems in humans?
Xeroderma pigmentosum
Chronic myelogenous leukemia results from
a chromosomal translocation which creates a fused gene that acts as an oncogene.
The p53 protein can arrest the cell cycle at the G1 stage by:
activating genes that encode proteins that stop the cell cycle
Which of the following organisms have the ability to repair DNA and thus minimize mutations?
all living things
Gene ______________ is a genetic event in which the number of copies of a gene is increased.
amplification
If DNA damage is too severe, the p53 protein will activate genes that promote ______.
apoptosis
In response to severe DNA damage that is too extensive to be repaired, the p53 protein will activate other genes that promote ___________________.
apoptosis
The scientific term for programmed cell death is ________________
apoptosis
In most cases, how many genetic changes in a cell lineage typically occur before cancer develops?
at least 10
In order for cancer cells from a lung carcinoma to metastasize, they must penetrate the ______ membrane, which is a sheetlike layer of extracellular matrix that provides a barrier between the lung cells and the bloodstream.
basement
A(n) _____________ tumor is precancerous and has not spread throughout the body.
benign
A(n) ______________ tumor is precancerous and has not spread throughout the body.
benign
The noninherited form of retinoblastoma usually occurs later in life because:
both copies of the gene must be mutated
A carcinogen is a chemical or physical agent that promotes:
cancer
The disease of multicellular organisms that is characterized by uncontrolled cell division is known as ____________________
cancer
Agents that increase the likelihood of developing cancer are known as ______________
carcinogens
Ultraviolet light and some chemicals in cigarette smoke are examples of mutagens called ___________ because they are known to cause cancer.
carcinogens
A ______ is a cancer of epithelial cells.
carcinoma
A cancer derived from epithelial cells is called a(n)
carcinoma
During apoptosis, what proteins degrade selected cellular proteins such as microfilaments?
caspases
______________ are enzymes that are activated during programmed cell death to digest certain cellular proteins such as actin filaments.
caspases
Some tumor-suppressor genes encode proteins that test the integrity of the genome and prevent a cell from progressing past a certain stage in the cell cycle. These proteins are termed ____________ proteins.
checkpoint
What proteins monitor the integrity of the genome and prevent a cell from progressing through a certain point in the cell cycle?
checkpoint proteins
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
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?
direct repair
Tumor-suppressor genes lead to cancer by mutations that:
eliminate their function
True or false: The function of a normal tumor-suppressor gene is to promote cell division.
false
Which of the following genetic changes can convert a proto-oncogene into an oncogene?
gene amplifications missense mutations chromosomal translocations
Relatively small changes in DNA sequence are known as:
gene mutations
The activity of an oncogene is:
higher than that of the normal gene
The Ames test uses a strain of Salmonella typhimurium that cannot synthesize:
histidine
The gene that encodes the Ras protein becomes an oncogene when a mutation reduces the ability of the protein to:
hydrolyze GTP
The Rb protein blocks cell division by:
inhibiting the E2F transcription factor
Tumors that are cancerous, spreading throughout the body and invading healthy tissues are ______.
malignant
The process by which cancerous cells spread through the body via the bloodstream or surrounding body fluids is termed _____________
mestasis
The process that occurs when cancer cells spread into the blood and other parts of the body is known as
metastasis
The expression of a tumor-suppressor gene may be reduced when CpG islands near its promoter region are
methylated
When the promoter of a tumor-suppressor gene undergoes abnormal ______, the transcription of the gene is usually inhibited.
methylation
Most carcinogens are also:
mutagens
Cancer usually affects older people because they are likely to have more:
mutations
The two main functions of tumor suppressor genes are:
negative regulation of cell division maintenance of genome integrity
A mutant gene that results in uncontrolled cell growth is known as a(n)
oncogene
Consider a normal gene that is needed for growth. If this gene becomes overactive, it may contribute to cancer. It then becomes a(n)
oncogene
The gene that encodes the Ras protein is an example of a(n):
oncogene
Over the past four decades, researchers have identified many types of ______. Examples include growth factor receptors, transcription factors, and intracellular signaling proteins. Multiple choice question.
oncogenes
Which type of genes result from mutations that increase the activity of normal genes?
oncogenes
When oncogenes are ______ compared to proto-oncogenes, they can promote certain types of cancer.
overactive
The protein product of what tumor-suppressor gene acts to sense DNA damage, promote DNA repair, and halt cell division?
p53
What gene is a tumor-suppressor gene?
p53
Apoptosis is a term that refers to:
programed cell death
Nucleotide excision repair (NER) is found in:
prokaryotes and eukaryotes
A missense mutation in a(n) ________________ -oncogene can convert it to a cancer-promoting gene if the mutation alters the function of the encoded protein to allow for increased cell division.
proto
A normal gene that can become an oncogene if it is mutated is called a(n) ______________ - ______________.
proto-ocogene
What gene is an oncogene?
ras
Individuals affected by xeroderma pigmentosum are likely to develop skin cancer because they cannot ______________ UV-induced lesions.
repair
Xeroderma pigmentosum causes a predisposition to skin cancer because it impairs the ability to:
repair UV-induced lesions
Based on the two-hit hypothesis, ______ requires two mutations to occur.
retinoblastoma
Amplification of a proto-oncogene can lead to cancer if it increases:
the amount of protein produced
A normal proto-oncogene may become an oncogene if it is:
translocated to a different chromosome mutated amplified
A genetic alteration called a chromosomal _____________________ occurs when one segment of a chromosome becomes attached to a different chromosome.
translocation
True or false: Carcinogens include UV light and certain chemicals in cigarette smoke.
true
True or false: Defects in DNA repair systems may lead to syndromes associated with photosensitivity and higher predisposition to skin cancer.
true
An overgrowth of cells is known as a(n) ______________ , which can be benign or become cancerous.
tumor
Elimination of the function of a(n) ______ gene promotes cancer.
tumor-suppressor
The protein p53 is encoded by a(n):
tumor-suppressor gene
Genes that normally function to prevent cancerous growth are called:
tumor-suppressor genes
Maintenance of genome integrity and negative regulation of cell division are the two main functions of:
tumor-suppressor genes
Genes encoding proteins involved in the regulation of normal cell growth and thus the prevention of cancer are called _____________ - _____________ genes.
tumor; suppressor
According to Alfred Knudson's hypothesis, the number of mutations that must occur in the Rb gene before an individual develops retinoblastoma is ____________
two
Cancer is characterized by:
uncontrolled cell division
The rate of spontaneous mutation is approximately:
10-6 per gene per cell division
Consider the following wild-type DNA sequence: 5'-CCAAGGTT-3'. Which of the following mutations is a base substitution?
5'-CCCAGGTT-3'
What is a point mutation?
A mutation that affects only a single base pair
What is a base substitution?
A mutation that occurs when one base is replaced by another
What is a mutagen?
A physical or chemical agent that causes mutations
How do point mutations affect DNA sequences?
By substituting one base for another By adding or subtracting a single base pair
What are the two main types of mutagens?
Chemical or physical
A spontaneous point mutation may be caused during DNA replication when the enzyme _____________ _____________ puts the wrong base in a newly-synthesized strand.
DNA polymerase
Which of the following are chemical mutagens?
Ethyl methanesulfonate Benzopyrene Nitrous acid Nitrogen mustard
What is the purpose of the Ames test?
Evaluation of the ability of a substance to cause mutation
True or false: Nonsense and frameshift mutations generally result in less dramatic changes to a polypeptide sequence than missense mutations.
False -- In general, nonsense and frameshift mutations have a much larger effect on protein structure and function than missense mutations. This is because missense mutations only affect a single amino acids, whereas nonsense and frameshift mutations have the potential to affect many. more.
Which of the following are TRUE regarding ionizing and nonionizing radiation?
Ionizing radiation can penetrate deeply into biological tissue, whereas nonionizing radiation can only penetrate the surface. Ionizing radiation is short wavelength with high energy, and nonionizing radiation has longer wavelengths with lower energy.
Which of the following statements is TRUE?
Larger genes are more likely to incur a mutation than smaller genes.
What type of mutation changes a single amino acid in a polypeptide sequence?
Missense
What is the approximate typical rate of spontaneous mutation per cell division?
One mutation for every 1 million genes
Mutations outside a gene's coding sequence can affect gene expression. Which of the following sites, when mutated, would affect transcription?
Operator site Promoter
How does a frameshift mutation affect protein function?
Protein function is most likely inhibited because an entirely new amino acid sequence occurs downstream of the mutation.
Where must a mutation occur if it is to directly affect an amino acid sequence?
The coding region of a structural gene
How are timing and size of the patch of tissue affected by a somatic mutation related?
The earlier in development the mutation occurs, the larger the patch.
How do somatic mutations affect an individual's offspring?
The mutation does not occur in germ line cells and therefore does not affect offspring.
______ 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
What type of radiation is nonionizing and only penetrates the surface of biological materials?
UV light
Which of the following are examples of ionizing radiation?
X-rays Gamma rays
A mutation is best defined as:
a heritable change in the genetic material
A missense mutation may not affect protein structure and function if the altered amino acid has:
a similar side chain
A chemical that resembles a normal base and therefore can substitute for it during DNA replication is said to be a(n)
base analogue.
Nitrous acid, nitrogen mustard, 5-bromouracil, and benzo(a)pyrene are examples of ______________ mutagens.
chemical
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
In the Ames test, rat liver extract is included because liver ____________ sometimes convert chemicals into mutagens.
enzymes
A(n) ________________ mutation typically inhibits protein function because it changes the amino acid sequence downstream of the mutation site.
frameshift
In what types of cells do germ line mutations occur?
gamete-producing precursors egg sperm
Exposure to chemical mutagens can lead to mutations because chemical mutagens can cause:
inappropriate base pairing during DNA replication insertions and deletions during DNA replication
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 DNA.
induced
Mutations in noncoding sequences:
may affect gene expression
A specific type of point mutation called a(n) _____________ mutation is a base substitution that changes a single amino acid in a polypeptide sequence.
missense
Which of the following are examples of somatic cells?
muscle cells skin cells liver cells
Agents that cause mutation are known as:
mutagens
UV light is an example of:
nonionizing radiation
A(n) _____________ mutation involves a change from a normal codon to a stop codon.
nonsense
In bacteria, the regulation of a gene's transcription can be altered if mutations occur in regulatory elements. For example a mutation in the ______ site of the lac operon may prevent the lac repressor from binding to it, thus causing constitutive expression of the operon.
operator
X-rays and ultraviolet light are examples of ______ mutagens.
physical
A mutation that affects only a single base pair within a DNA sequence is called a(n) ________________ mutation.
point
In the Lederberg experiment, bacterial colonies on replica plates were exposed to T1 bacteriophage. The results of this experiment demonstrated that the mutation conferring resistance to the bacteriophage occurred:
prior to phage exposure randomly
Mutations that occur in noncoding sequences may affect gene
regulation
Biologists categorize the causes of mutation as _____________, which result from errors in normal processes, or induced, which are caused by external agents.
spontaneous
What type of mutation results from abnormalities that naturally occur during biological processes?
spontaneous
Silent mutations have no effect on the amino acid sequence of a polypeptide because:
the base substitution results in a codon that specifies the same amino acid as the original sequence
Nonionizing radiation, such as ultraviolet light, can lead to:
the formation of a thymine dimer
Somatic mutations are not transmitted to an individual's offspring because:
they do not occur in the gametes
True or false: Larger genes are usually more likely to incur a mutation than smaller genes.
true
True or false: New mutations are much more likely to be harmful than beneficial to the individual.
true
True or false: The earlier in development a somatic mutation occurs, the larger the patch of tissue that will be affected by that mutation. True false question.
true
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; 50
A mutation in a germline cell has a(n) ____________ percent chance of being transmitted from parent to child.
50
What is the chance that a mutation in a parent's germ line cells will be passed on to his or her offspring?
50%
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.
What is an example of how mutation in an operator site alters regulation of gene transcription?
A change of a DNA sequence in E. coli so that the lac repressor protein no longer binds to it
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.
How do environmental agents that cause induced mutations affect the mutation rate?
They increase the mutation rate compared to the spontaneous mutation rate.
How do nonsense mutations affect protein function?
Translation is terminated where the mutation occurs, producing a truncated polypeptide which is unlikely to function correctly.
The compound 5-bromouracil has a structure that is similar to that of a particular base in DNA and can substitute for it. When incorporated into DNA, it can also cause errors in DNA replication. Thus, 5-bromouracil is said to be a base ________________
analogue
Mutagens can be categorized into ________ or ________ mutagens.
chemical; physical
A silent mutation results in a polypeptide with an unchanged amino acid sequence because the genetic code is:
degenerate
The results of the replica plating experiment performed by Joshua and Esther Lederberg supported their hypothesis that mutations are random events by demonstrating that the tonr mutation:
developed in the original population before exposure to bacteriophages.
Germ-line mutations may occur in ____________ cells, ____________ cells, or in the precursor cells that produce them.
egg; sperm
Induced mutations are caused by:
environmental agents
What type of mutation is the result of the insertion or removal of nucleotides that does not occur in multiples of three?
frameshift
Mutations are essential for the long-term continuity of life because they supply the ________________ variation that is the foundation for evolutionary change.
gene
Cells that give rise to gametes, such as egg and sperm cells, are known as the ________________ ________________ cells.
germ line
Gametes are produced by:
germ line cells
Exposure to agents that result in induced mutations causes the mutation rate of a cell to be ___________ than the spontaneous mutation rate.
higher
________________ radiation is short-wavelength and high energy, including X-rays and gamma rays, and often leads to base deletions and breaks in one or both DNA strands. On the other hand, ________________ radiation has a longer wavelength and lower energy, such as UV light, which penetrates the skin and often leads to thymine dimers.
ionizing; nonionizing
What type of mutation changes a normal codon to a termination codon?
nonsense
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 as ____________ ____________.
replica plating
The Lederbergs used a procedure called _______________ _______________ to demonstrate that mutations are random events. The procedure involves transferring cells from bacterial colonies on a master to a secondary plate that contains T1 bacteriophages.
replica plating
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
Sperm and egg cells are termed germ line cells. In contrast, cells of the skin, muscle, heart, and liver are examples of ____________ cells.
somatic
A nonsense mutation causes the _____________ of the protein to be terminated prematurely. This reduces the length of the polypeptide and thus alters its function.
translation
What is a thymine dimer?
A site where two adjacent thymine bases become covalently cross-linked to each other
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.
The ____________ test, which was developed in the 1970s, is used to evaluate the ability of a substance to cause mutations.
Ames
Mutations that do not alter the amino acid sequence of a polypeptide are known as ______________ mutations.
silent
What type of mutation has no effect on the amino acid sequence of a polypeptide?
silent
Mutagens can be categorized into ______________ or ______________ mutagens.
chemical; physical
A heritable change in genetic material is known as a(n)
mutation
A point mutation in which one base pair is replaced by another is known as a(n) base
substitution
When the addition or deletion of nucleotides does not occur in a multiple of ________________ nucleotides, the result is a frameshift mutation.
three
Which of the following are ways that ionizing radiation can alter DNA structure?
Base deletion Breaks in one or both DNA strands
A ______________ ______________ is a site where two adjacent thymine bases become covalently cross-linked to one another.
thymine dimer
X-rays and gamma rays are examples of ______________ radiation, which is a type of electromagnetic radiation that can create free radicals.
ionizing
A mutation occurs in a single cell during embryonic development. The cell continues to divide to produce a streak of white hair in the individual. This is an example of a(n) _______________ mutation.
somatic
All cells of the body that are not part of the germ line are called ____________ cells.
somatic
A mutation may affect the amino acid sequence of a polypeptide only if it occurs within the
coding sequence of a structural gene.