Chapter 14: Gene Mutation, Repair, and Transposition Flashcards
True or False. A mutation can be defined as an alteration in DNA sequence. Any base-pair change in any part of a DNA molecule can be considered a mutation.
True
True or False. Mutations that occur in somatic cells are heritable and are the basis for the transmission of genetic diversity and evolution, as well as genetic diseases.
False. Germ cells
The type of mutation that involves a change of one base pair to another in a DNA molecule.
Point mutation or Base substitution
A change of one nucleotide of a triplet within a protein-coding portion of a gene may result in the creation of a new triplet that codes for a different amino acid in the protein product. This type of mutation is called?
Missense mutation
A change of one nucleotide of a triplet within a protein-coding portion of a gene may result in the creation of a stop codon. This mutation is called?
Nonsense mutation
If the point mutation alters a codon but does not result in a change in the amino acid at that position in the protein (due to degeneracy of the genetic code), this mutation is called?
Silent mutation
In a base substitution mutation, a pyrimidine replaces a pyrimidine or a purine replaces a purine. This mutation is referred to as?
Transition mutation
In a base substitution mutation, a purine replaces a pyrimidine or vice versa. This mutation is referred to as?
Transversion mutation
A mutation, either an insertion or deletion of nucleotides, that alters the triplet reading frame is called?
Frameshift mutation
True or False. A frameshift mutation will occur when any number of bases are added or deleted, except multiples of three, which would reestablish the initial frame of reading.
True
A type of mutation that reduces or eliminates the function of the gene product.
Loss-of-function mutation
Mutations that result in complete loss of function are known as?
Null mutations
True or False. Most loss-of-function mutations are dominant.
False. Recessive
Results in a wild-type phenotype when present in a diploid organism and the other allele is wild type.
Recessive mutation
Results in a mutant phenotype in a diploid organism, even when the wild-type allele is also present.
Dominant mutation
Occurs when the single wild-type copy of the gene does not produce enough gene product to bring about a wild-type phenotype.
Haploinssufficiency
This disease in humans is an example of a disorder caused by haploinsufficiency—in this case as a result of a loss-of-function mutation in one copy of the FBN1 gene.
Marfan syndrome
This mutation results in a gene product with enhanced, negative, or new functions.
Dominant gain-of-function mutation
Causes of dominant gain-of-function mutation.
- Change in the amino acid sequence of the protein that confers a new activity
- A mutation in a regulatory region of the gene, leading to expression of the gene at higher levels or at abnormal times or places.
This type of mutation may directly interfere with the function of the product of the wild-type allele. Often this occurs when the mutant nonfunctional gene product binds to the wild-type gene product, inactivating it.
Dominant negative mutation
These mutations are recognized by their ability to alter a normal or wild-type visible phenotype.
Visible mutation
This mutation results in a loss of ability to synthesize an amino acid or vitamin.
Nutritional mutation
Although these kinds of mutations do not always affect morphological characters, they affect the function of proteins that can impinge on the well-being and survival of the affected individual.
Biochemical mutation
This category of mutations consists of mutations that affect the behavior patterns of an organism.
Behavioral mutations
This kind of mutation disrupts a regulatory gene or a gene control region which results in the disruption of the normal regulatory processes and inappropriate activation or inactivation of a gene.
Regulator mutations
This kind of mutation adversely affects a gene product that is essential to the survival of the organism.
Lethal mutation
These mutations are present in the genome of an organism but can be detected only under certain conditions.
Conditional mutations
This is a type of conditional mutation whereby at a “permissive” temperature, the mutant gene product
functions normally, but it loses its function at a different, “restrictive” temperature.
Temperature-senstive mutations
A mutation that can occur either in a protein-coding region or in any part of the genome, and its effect on the genetic fitness of the organism is negligible.
Neutral mutation
Mutations that are occurring in any cell in the body except germ cells.
Somatic mutations
Are mutations within genes located on the autosomes.
Autosomal mutations
Are mutations within genes located on the X chromosome.
X-linked mutation
Are mutations within genes located on the Y chromosome.
Y-linked mutation
True or False. Somatic mutations will have a greater impact if they are dominant or, in males, if they are X-linked since such mutations are most likely to be immediately expressed.
True
Are mutations in the nucleotide sequence of genes that appear to occur naturally.
Spontaneous mutation
Are mutations that result from the influence of extraneous factors.
Induced mutations
Defined as the likelihood that a gene will undergo a mutation in a single generation or in forming a single gamete.
Mutation rate
Some DNA sequences appear to be highly susceptible to mutation and are known as?
Mutation Hotspot
Are alternate chemical forms that differ by only a single proton shift in the molecule.
Tautomers
The biologically important tautomers:
- keto-enol forms of thymine
2. amino-imino forms of cytosine and adenine
This shift changes the bonding structure of the molecule, allowing hydrogen bonding with noncomplementary bases.
Tautomeric shift
The loss of one of the nitrogenous bases in an intact double-helical DNA molecule. Most frequently, the base is a purine—either guanine or adenine.
Depurination
This results if the glycosidic bond linking the 1′-C of the deoxyribose and the number 9 position of the purine ring is broken.
Apurinic site
An amino group in cytosine or adenine is converted to a keto group. The major effect of these changes is an alteration in the base-pairing specificities of these two bases during DNA replication.
Deamination
DNA may also suffer damage from the by-products of normal cellular processes. These damages are often caused by reactive oxygen species (electrophilic oxidants) that are generated during normal aerobic respiration.
Oxidative damage
Are mutations that increase the rate of mutation above the spontaneous background.
Induced mutations
Agents that have the potential to damage DNA and cause induced mutations.
Mutagens
Compounds that can substitute for purines or pyrimidines during nucleic acid biosynthesis.
Base Analogs
A derivative of uracil, behaves as a thymine analog but is halogenated at the number 5 position of the pyrimidine ring.
5-bromouracil (5-BU)
If 5-BU is chemically linked to deoxyribose, what nucleoside analog is formed?
bromodeoxyuridine (BrdU)
This molecule can act as na analog of adenine.
2-amino purine (2-AP)
These substances donate an alkyl group, such as CH3 or CH3CH2 to amino or keto groups in nucleotide.
Alkylating agents
An alkylating agent that alkylates the keto groups in the number 6 position of guanine and in the number 4 position of thymine.
Ethylmethane sulfonate (EMS)
Are chemicals that have dimensions and shapes that allow them to wedge between the base pairs of DNA.
Intercalating agents
A substance that covalently binds to DNA, altering its conformation and interfering with replication and repair.
Adduct-forming agents
Are cancer-causing chemicals that are created during the cooking of meats such as beef, chicken, and fish. They are formed at high temperatures from amino acids and creatine.
Heterocyclic amines (HCAs)
Chemical species resulting from increased amount of UV introduced to the DNA and are consist of two thymine residues.
Pyrimidine dimers
Radiation that causes ionization of the molecules.
Ionizing radiation
These are chemical species containing one or more unpaired electrons.
Free-radicals
These are genetic disease caused by variations in several genes.
Polygenic
These are genetic disease caused by variations in single-gene mutations.
Monogenic
During this repair mechanism, the mismatches are detected, the incorrect nucleotide is removed, and the correct nucleotide is inserted in its place.
Mismatch repair
The process of strand discrimination is based on?
DNA methylation
This enzyme methylates adenine upon its addition to the growing DNA sequence. Prior to methylation, however, it also detects base mismatches.
Adenine methylase
This enzyme nicks the backbone of the unmethylated DNA (either in the 5’ or 3’ end of the mismatch) due to mismatching as detected by the adenine methylase.
Endonuclease
This enzyme unwinds and degrades the nicked DNA strand until the region of the mismatch is reached.
exonuclease
The human equivalent of MutH, MutL, and MutS genes. Associated with hereditary nonpolyposis colon cancer.
hMSH2, hMLH1 genes
This repair mechanism responds after damaged DNA has escaped repair and has failed to be completely replicated.
postreplication repair
Because the recombinational event is involved in postreplicational repair, it is considered to be?
homologous recombination repair.
This protein directs the recombinational exchange with the corresponding region on the undamaged parental strand of the same polarity (the “donor” strand).
RecA
In the presence of a large number of un-repaired DNA mismatches and gaps, bacteria can induce the expression of about 20 genes (including lexA, recA, and uvr) whose products allow DNA replication to occur even in the presence of these lesions. The repair mechanism is referred to as?
SOS repair system
True or False. During SOS repair, DNA synthesis becomes error-prone, inserting random and possibly incorrect nucleotides in places that would normally stall DNA replication. As a
result, SOS repair itself becomes mutagenic—although it may allow the cell to survive DNA damage that would
otherwise kill it.
True
UV-induced damage to E. coli DNA can be partially reversed if, following irradiation, the cells are exposed briefly to light in the blue range of the visible spectrum. This repair mechanism is called?
Photoreactivation repair
Photoreactivation repair is directed by which enzyme?
photoreactivation enzyme (PRE)
This type of excision repair mechanism corrects DNA that contains a damaged DNA base.
Base-excision repair
The first step in the base excision repair pathway in E. coli involves the recognition of the altered base by an enzyme called?
DNA glycosylase
In a base excision repair, the DNA glycosylase first cut the glycosidic bond between the base and the sugar, creating a?
apyrimidinic (if the base is pyrimidine) apurinic (if the base is purine) site
In a base excision repair, the apurinic/apyrimidic site is recognized by?
AP endonuclease (makes a cut in the
phosphodiester backbone at the apyrimidinic or apurinic
site)
This type of excision repair mechanism repair
“bulky” lesions in DNA that alter or distort the double helix. These lesions include the UV-induced pyrimidine dimers and DNA adductss.
Nucleotide excision repair (NER)
In the Nucleotide excision repair pathway products of this gene group are involved in recognizing and clipping out lesions in the DNA.
uvr (ultraviolet repair) genes - uvrA, uvrB, uvrC
A rare recessive genetic disorder that predisposes
individuals to severe skin abnormalities, skin cancers, and a wide range of other symptoms including developmental
and neurological defects.
xeroderma pigmentosum (XP) (results from defects in NER pathways)
XP patients were deficient in DNA synthesis other than that
occurring during chromosome replication. The later phenomenon is called?
unscheduled DNA synthesis
It is a single cell with two nuclei from different organisms but a common cytoplasm.
Heterokaryon
Are activated and are responsible for reattaching two broken DNA strands.
double-strand break repair (DSB repair) either (homologous recombination repair or nonhomologous end joining)
A double-strand break repair mechanism that does not recruit a homologous region of DNA during repair.
nonhomologous end joining
A double-strand break repair mechanism that involves the interaction of two sister chromatids is necessary because, when both strands of one helix are broken, there is no undamaged parental DNA strand available to use as a source of the complementary template DNA sequence during the repair.
homologous recombination repair
True or False. DSB repair usually occurs during the late S or early G2 phase of the cell cycle, after DNA replication, a time when sister chromatids are available to be used as repair templates.
True
This method uses a number of different strains of the
bacterium Salmonella typhimurium that have been selected for their ability to reveal the presence of specific types of mutations.
Ames test
Are cancer-causing agent
carcinogens
Can move or transpose within and between chromosomes, inserting themselves into various locations within the genome.
Transposable elements or transposon or jumping genes
This type of transposon can move from one location to
another and, if they insert into a gene or gene-regulatory region, may cause mutations.
Insertion sequences (IS elements)
This enzyme, encoded by a gene present in insertion sequence elements, is responsible for making staggered cuts in chromosomal DNA, into which the IS element can insert.
Transposase
These are short segments of DNA that have the same nucleotide sequence as each other but are oriented in the opposite direction. They are situated at the ends of IS elements.
inverted terminal repeats (ITRs)
Are larger than IS elements and contain protein-coding genes that are unrelated to their transposition.
Bacterial transposons
These elements are transcribed into “copious” amounts of RNA, hence the name.
copia
A condition characterized by sterility, elevated mutation
rates, and chromosome rearrangements in the offspring of crosses between certain strains of fruit flies..
hybrid dygenesis
Hybrid dysgenesis is caused by high rates of ______ transposition in the germ line, in which transposons insert themselves into or near genes, thereby causing mutations.
P element
One of the most useful applications of P elements is as vectors to introduce transgenes into Drosophila—a technique known as ?
germ-line transformation
