Download Raven/Johnson Biology 8e Chapter 17 Answers 1. A recombinant

Raven/Johnson Biology 8e
Chapter 17 Answers
1. A recombinant DNA molecules is one that is—
a. produced through the process of crossing over that occurs in meiosis
b. constructed from DNA from different sources
c. constructed from novel combinations of DNA from the same source
d. produced through mitotic cell division
The correct answer is b—
A. Answer a is incorrect. Crossing over produces novel combinations of DNA from a single
individual. The offspring are called recombinants.
The correct answer is b—constructed from DNA from different sources
B. Answer b is correct. Recombinant DNA is constructed in a laboratory and manipulated
for a specific purpose.
The correct answer is b—
C. Answer c is incorrect. New genetic combinations from the same individual occur as a
product of crossing over during meiosis. Recombinant DNA is an artificial construct that
uses DNA from different sources.
The correct answer is b—
D. Answer d is incorrect. Mitosis is the asexual form of cell division that produces
genetically identical daughter cells. There is no recombination of DNA during mitosis.
2. Type II restriction endonucleases are useful because—
a. they degrade DNA from the 5′ end
b. they cleave the DNA at random locations
c. they cleave the DNA at specific sequences
d. they only cleave modified DNA
The correct answer is c—
A. Answer a is incorrect. The ability to cleave DNA from an end is a property of an
exonuclease. Endonucleases work by breaking bonds within the DNA molecule.
The correct answer is c—
B. Answer b is incorrect. Type II enzymes recognize and cut a specific site, not at random
sites.
The correct answer is c—they cleave the DNA at specific sequences
C. Answer c is correct. A type II restriction endonuclease works by cleaving the DNA at
specific sequences. This property is used in many experimental techniques that involve
the manipulation of DNA.
The correct answer is c—
D. Answer d is incorrect. The cells that produce these enzymes protect their own DNA
because they do not work on modified DNA.
3. What is the basis of separation of DNA fragments by gel electrophoresis?
a. The negative charge on DNA
b. The size of the DNA fragments
Raven/Johnson Biology 8e
Chapter 17 Answers
c. The sequence of the fragments
d. The presence of a dye
The correct answer is b—
A. Answer a is incorrect. The negative charge is necessary to cause the movement of the
DNA fragments through the gel.
The correct answer is b—The size of the DNA fragments
B. Answer b is correct. Different size fragments move at different speeds with small
fragments moving more quickly than larger fragments.
The correct answer is b—
C. Answer c is incorrect. The sequence of the fragments does not contribute to the
separation.
The correct answer is b—
D. Answer d is incorrect. Dyes are used to visualize the fragments, but they do not contribute
to the separation.
4. How is the gene for β-galactosidase used in the construction of a plasmid?
a. The gene is a promoter that is sensitive to the presence of the sugar, galactose.
b. It is an origin of replication.
c. It is a cloning site.
d. It is a marker for insertion of DNA.
The correct answer is d—
A. Answer a is incorrect. Promoters are binding sites for RNA polymerase.
The correct answer is d—
B. Answer b is incorrect. Beta-galactosidase is an enzyme not an origin of replication.
The correct answer is d—
C. Answer c is incorrect. The gene for β-galactosidase is located in cloning sites, but is not
itself a cloning site.
The correct answer is d—It is a marker for insertion of DNA.
D. Answer d is correct. When DNA is inserted into the plasmid, the function of this enzyme
is disrupted. The absence of color formation is a marker for recombination.
5. The basic logic of enzymatic DNA sequencing is to produce—
a. a nested set of DNA fragments produced by restriction enzymes
b. a nested set of DNA fragments that each begin with different bases
c. primers to allow PCR amplification of the region between the primers
d. a nested set of DNA fragments that end with known bases
The correct answer is d—
A. Answer a is incorrect. Restriction enzymes cut specific sites but not frequently enough to
allow sequencing.
Raven/Johnson Biology 8e
Chapter 17 Answers
The correct answer is d—
B. Answer b is incorrect. It is important during enzymatic sequencing that the fragments all
begin from the same primer, because they are then terminated at different bases.
The correct answer is d—
C. Answer c is incorrect. PCR amplification is now used for sequencing, but the logic still
requires generating a nested set of fragments that end with the same base.
The correct answer is d—a nested set of DNA fragments that end with known bases
D. Answer d is correct. The logic still requires generating a nested set of fragments that end
with the same base. This is accomplished using nucleotides that act as chain terminators.
6. A DNA library is—
a. an orderly array of all the genes within an organism
b. a collection of vectors
c. the collection of plasmids found within a single E. coli
d. a collection of DNA fragments representing the entire genome of an organism
The correct answer is d—
A. Answer a is incorrect. Genomic libraries are made up of random fragments of DNA from
the entire genome, not just genes.
The correct answer is d—
B. Answer b is incorrect. A library is a collection of vectors with DNA inserted into them.
The correct answer is d—
C. Answer c is incorrect. Multiple cells are required to hold all the vectors that carry the
various DNA inserts that make up a genomic library.
The correct answer is d—a collection of DNA fragments representing the entire genome of an
organism
D. Answer d is correct. A genomic library is a collection of random DNA fragments from the
entire genome.
7. Molecular hybridization is used to—
a. generate cDNA from mRNA
b. introduce a vector into a bacterial cell
c. screen a DNA library
d. introduce mutations into genes
The correct answer is c—
A. Answer a is incorrect. The enzyme reverse transcriptase is used to make cDNA from
mRNA.
The correct answer is c—
B. Answer b is incorrect. Molecular hybridization refers to the ability of a labeled probe to
bind to its complementary sequence in denatured DNA.
The correct answer is c—screen a DNA library
Raven/Johnson Biology 8e
Chapter 17 Answers
C. Answer c is correct. Molecular hybridization refers to the ability of a labeled probe to
bind to its complementary sequence in denatured DNA. This property is used to identify
the presence of genes of interest within large DNA collections like libraries.
The correct answer is c—
D. Answer d is incorrect. Molecular hybridization refers to the ability of a labeled probe to
bind to its complementary sequence in denatured DNA.
8. The enzyme used in the polymerase chain reaction is—
a. a restriction endonuclease
b. heat-resistant RNA polymerase
c. reverse transcriptase
d. a heat-resistant DNA polymerase
The correct answer is d—
A. Answer a is incorrect. Restriction endonucleases are used to break up DNA. They are not
part of the polymerase chain reaction.
The correct answer is d—
B. Answer b is incorrect. PCR generates DNA fragments, not RNA.
The correct answer is d—
C. Answer c is incorrect. Reverse transcriptase is used to convert RNA into DNA. PCR uses
DNA as its template.
The correct answer is d—a heat-resistant DNA polymerase
D. Answer d is correct. PCR synthesizes DNA strands from a DNA template. The specific
enzyme used, Taq polymerase, needs to be heat-resistant because the reaction cycles
through high- and low-temperature phases.
9. How does the yeast two-hybrid system detect protein–protein interactions?
a. Binding of fusion partners triggers a signal cascade that alters gene expression.
b. Fusion partners are detected using radioactive probes of Western blots.
c. Protein–protein binding of fusion partners triggers expression of a reporter gene.
d. Protein–protein binding of fusion partners triggers expression of the Gal4 gene.
The correct answer is c—
A. Answer a is incorrect. The fusion partners are two parts of the Gal4 transcriptional
activator. No signal cascade is involved.
The correct answer is c—
B. Answer b is incorrect. The fusion partners are two parts of the transcriptional activator,
Gal4. Gal4 activity results in a change in gene expression.
The correct answer is c—Protein–protein binding of fusion partners triggers expression of a
reporter gene.
C. Answer c is correct. If the fusion partners can bind, then Gal4 becomes functional and
will trigger the expression of a reporter gene linked to the Gal4 promoter.
Raven/Johnson Biology 8e
Chapter 17 Answers
The correct answer is c—
D. Answer d is incorrect. The fusion partners are hybrid proteins linking part of the Gal4
transcription activator with a protein of interest. Fusion partner binding triggers
expression of a gene downstream from the Gal4 promoter.
10. In vitro mutagenesis is used to—
a. produce large quantities of mutant proteins
b. create mutations at specific sites within a gene
c. create random mutations within multiple genes
d. create organisms that carry foreign genes
The correct answer is b—
A. Answer a is incorrect. The production of large quantities of proteins is made possible by
expression vectors.
The correct answer is b—create mutations at specific sites within a gene
B. Answer b is correct. Scientists use in vitro mutagenesis to examine the effect of specific
changes in gene sequence of the function of the protein product.
The correct answer is b—
C. Answer c is incorrect. In vitro mutagenesis allows for the generation of known mutations.
The correct answer is b—
D. Answer d is incorrect. Transgenic organisms carry foreign genes.
11. Insertion of a gene for a surface protein from a medically important virus such as herpes
into a harmless virus is an example of—
a. a DNA vaccine
b. reverse genetics
c. gene therapy
d. a subunit vaccine
The correct answer is d—
A. Answer a is incorrect. A DNA vaccine is based on splicing an internal protein into a
plasmid to trigger a cellular immune response.
The correct answer is d—
B. Answer b is incorrect. Reverse genetics refers to the use of genetic knockouts to examine
the role of a specific gene.
The correct answer is d—
C. Answer c is incorrect. Gene therapy involves the integration of a functional gene into an
organism to replace or repair an existing genetic mutation.
The correct answer is d—a subunit vaccine
D. Answer d is correct. Subunit vaccines are based on packaging a gene for a unique marker
protein for a pathogenic virus within a nonpathogenic virus which protects the individual
by priming the immune response without exposing the person to the dangerous virus.
Raven/Johnson Biology 8e
Chapter 17 Answers
12. What is a Ti plasmid?
a. A vector that can transfer recombinant genes into plant genomes
b. A vector that can be used to produce recombinant proteins in yeast
c. A vector that is specific to cereal plants like rice and corn
d. A vector that is specific to embryonic stem cells
The correct answer is a—A vector that can transfer recombinant genes into plant genomes
A. Answer a is correct. The Ti plasmid can trigger the integration of the genes within the
plasmid into a plant cell’s chromosome. In this way all the cells that arise from the
transfected cell will carry the recombinant protein.
The correct answer is a—
B. Answer b is incorrect. The Ti plasmid is specific to the plant bacteria Agrobacterium.
The correct answer is a—
C. Answer c is incorrect. The Ti plasmid normally does not transfecting cereal plants. It has
now been modified to allow use with cereals.
The correct answer is a—
D. Answer d is incorrect. The Ti plasmid is specific for plants.
13. Which of the following is NOT a possible benefit of genetically modified crops?
a. Increased nutritional value for people
b. Enhanced resistance to insect pests
c. Enhanced resistance to broad spectrum herbicides
d. Enhanced resistance to insecticides
The correct answer is d—
A. Answer a is incorrect. Golden Rice is an example of a genetically modified crop with
improved nutritional properties for humans.
The correct answer is d—
B. Answer b is incorrect. Bt crops are genetically modified to produce insecticidal proteins.
The correct answer is d—
C. Answer c is incorrect. Crops genetically engineered to overexpress EPSP synthase are an
example of a plant that will resist herbicides.
The correct answer is d—Enhanced resistance to insecticides
D. Answer d is correct. Plants do not have to resist insecticides.
Challenge Questions
1. Many human proteins, such as hemoglobin, are only functional as an assembly of
multiple subunits. Assembly of these functional units occurs within the endoplasmic
reticulum and Golgi apparatus of a eukaryotic cell. Discuss what limitations, if any,
exist to the large-scale production of genetically engineered hemoglobin.
Raven/Johnson Biology 8e
Chapter 17 Answers
Answer—Genetic engineering often means insertion of a gene of interest (and harvest of the
protein of interest) from vast numbers of bacterial cells. Bacteria are prokaryotes, and as such do
not have internal membrane systems like the endoplasmic reticulum and Golgi apparatus. An
alternative would be to use a yeast system since yeast cells are eukaryotes. In either case, one of
the major limiting factors is the ability to efficiently harvest the protein of interest and purify it
away from all the other proteins normally produced by the host cell.
2. Enzymatic sequencing of a short strand of DNA was completed using
dideoxynucleotides. Use the gel shown to determine the sequence of that DNA.
G
C
A
T
Answer—Read the gel starting from the smallest fragment (at the bottom) to the largest. The
sequence is: CTGATAGTCAGCTG