chapata

Chapter 12A—DNA and RNA

MULTIPLE CHOICE

1. What did Griffith observe when he injected into mice a mixture of heat-killed disease-causing bacteria and live harmless bacteria?
a.
The disease-causing bacteria changed into harmless bacteria.
b.
The mice developed pneumonia.
c.
The harmless bacteria died.
d.
The mice were unaffected.

ANS: B PTS: 1 REF: p. 288

2. Which of the following is a nucleotide found in DNA?
a.
ribose + phosphate group + thymine
b.
ribose + phosphate group + uracil
c.
deoxyribose + phosphate group + uracil
d.
deoxyribose + phosphate group + cytosine

ANS: D PTS: 1 REF: p. 291

3. DNA replication results in two DNA molecules,
a.
each with two new strands.
b.
one with two new strands and the other with two original strands.
c.
each with one new strand and one original strand.
d.
each with two original strands.

ANS: C PTS: 1 REF: p. 299

4. During mitosis, the
a.
DNA molecules unwind.
b.
histones and DNA molecules separate.
c.
DNA molecules become more tightly coiled.
d.
nucleosomes become less tightly packed.

ANS: C PTS: 1 REF: p. 296

5. Unlike DNA, RNA contains
a.
adenine.
c.
phosphate groups.
b.
uracil.
d.
thymine.

ANS: B PTS: 1 REF: p. 300

6. Which type(s) of RNA is(are) involved in protein synthesis?
a.
transfer RNA only
b.
messenger RNA only
c.
ribosomal RNA and transfer RNA only
d.
messenger RNA, ribosomal RNA, and transfer RNA

ANS: D PTS: 1 REF: p. 300

7. During transcription, an RNA molecule is formed
a.
that is complementary to both strands of DNA.
b.
that is complementary to neither strand of DNA.
c.
that is double-stranded.
d.
inside the nucleus.

ANS: D PTS: 1 REF: p. 301

8. How many codons are needed to specify three amino acids?
a.
3
c.
9
b.
6
d.
12

ANS: A PTS: 1 REF: p. 302

9. Which of the following terms is LEAST closely related to the others?
a.
intron
c.
polypeptide
b.
tRNA
d.
anticodon

ANS: A PTS: 1 REF: p. 302

10. Which type of RNA functions as a blueprint of the genetic code?
a.
rRNA
c.
mRNA
b.
tRNA
d.
RNA polymerase

ANS: C PTS: 1 REF: p. 301

11. Which of the following is NOT a gene mutation?
a.
inversion
c.
deletion
b.
insertion
d.
substitution

ANS: A PTS: 1 REF: p. 308

12. Which of the following statements is true?
a.
A promoter determines whether a gene is expressed.
b.
An expressed gene is turned off.
c.
Proteins that bind to regulatory sites on DNA determine whether a gene is expressed.
d.
RNA polymerase regulates gene expression.

ANS: C PTS: 1 REF: p. 310

13. A lac repressor turns off the lac genes by binding to
a.
the promoter.
c.
the operator.
b.
tRNA.
d.
the lac genes.

ANS: C PTS: 1 REF: p. 310

14. Gene regulation in eukaryotes
a.
usually involves operons.
b.
is simpler than in prokaryotes.
c.
allows for cell specialization.
d.
includes the action of DNA polymerase.

ANS: C PTS: 1 REF: p. 311

15. Which of the following statements is NOT true?
a.
Mutations do not occur in hox genes.
b.
Hox genes that are found in different animals are very different from each other.
c.
Hox genes control the normal development of an animal.
d.
Hox genes occur in clusters.

ANS: B PTS: 1 REF: p. 312

COMPLETION

1. The structure labeled X in Figure 12-1 is a(an) ____________________.

Figure 12–1

ANS: nucleotide

PTS: 1 REF: p. 294

2. The order of nitrogenous bases in DNA determines the order of ____________________ in proteins.

ANS: amino acids

PTS: 1 REF: p. 302

3. There is no ____________________ that is specified by a stop codon on an mRNA molecule.

ANS: amino acid

PTS: 1 REF: p. 303

4. The lac repressor releases the operator in the presence of ____________________.

ANS: lactose

PTS: 1 REF: p. 310

5. In eukaryotes, proteins that attract RNA polymerase bind to ____________________ sequences in DNA.

ANS: enhancer

PTS: 1 REF: p. 311

SHORT ANSWER

1. At the beginning of DNA replication, what two processes “unzip” the two strands of a DNA molecule?

ANS:
The hydrogen bonds between the base pairs must be broken and the molecule must unwind.

PTS: 1 REF: p. 299

2. In Figure 12-2, which molecule is tRNA, and what is its function?

Figure 12–2

ANS:
Molecule B is tRNA, which carries amino acids to the ribosomes.

PTS: 1 REF: p. 301

3. According to Figure 12-3, what codons specify the amino acid arginine?

Figure 12–3

ANS:
AGG, AGA, CGA, CGC, CGU, and CGG specify arginine.

PTS: 1 REF: p. 303

4. What happens to lac repressors in E. coli when lactose is present?

ANS:
Lactose binds to the lac repressor, causing the repressor to release the operator.

PTS: 1 REF: p. 310

5. Why are hox genes that are found in different animals very similar to one another?

ANS:
The hox genes descended from the genes of common ancestors.

PTS: 1 REF: p. 312

ESSAY

1. Describe the Hershey-Chase experiment. Why were the results important?

ANS:
Hershey and Chase grew bacteriophages in cultures containing radioactive isotopes of 32P and 35S. The 32P became incorporated into the bacteriophage’s DNA because DNA contains phosphorus. The 35S became incorporated into the bacteriophage’s protein coat because proteins contain sulfur. After the bacteriophages were allowed to infect bacteria, Hershey and Chase found that nearly all the radioactivity in the bacteria was from 32P. This indicated that the bacteriophage’s DNA was injected into the bacteria. The results were important because they showed that the bacteriophage’s genetic material was DNA, not protein.

PTS: 1 REF: p. 289 | p. 290

2. Describe the structure of a DNA molecule.

ANS:
A DNA molecule has the shape of a double helix, or that of a twisted ladder. Each strand of the helix is a chain of nucleotides. Each nucleotide is made up of a deoxyribose sugar, a phosphate group, and a nitrogenous base. The two strands are held together by hydrogen bonds between the nitrogenous bases of the nucleotides on opposite strands. The nitrogenous bases form hydrogen bonds with each other in pairs. Adenine forms hydrogen bonds with thymine, and guanine forms hydrogen bonds with cytosine.

PTS: 1 REF: p. 294

3. Contrast the functions of the three main types of RNA.

ANS:
Messenger RNA carries copies of instructions for assembling proteins from DNA to the ribosomes. Ribosomal RNA is a component of the ribosomes. Transfer RNA carries amino acids to the ribosomes for assembly into proteins.

PTS: 1 REF: p. 301

4. Mendel might have been surprised to learn that genes simply contain the instructions for assembling proteins. What do proteins have to do with the phenotype of an organism?

ANS:
Proteins have many different functions in an organism. These functions include catalyzing and regulating chemical reactions, regulating growth patterns, and providing the actual structural components of the organisms. Together, these functions play a key role in producing an organism’s traits, or phenotype.

PTS: 1 REF: p. 306

5. Why do some kinds of point mutations cause greater changes in proteins than others?

ANS:
Point mutations include substitutions, insertions, and deletions of single nucleotides in DNA. Insertions and deletions have a greater effect on proteins than do substitutions, because insertions and deletions change the reading frame of the genetic code, affecting every amino acid that follows the point of mutation. In contrast, a substitution affects a single amino acid. A change in more than one amino acid is more likely to alter the function of the protein than is a change in a single amino acid.

PTS: 1 REF: p. 307

OTHER

USING SCIENCE SKILLS

Figure 12–4

1. Interpreting Graphics What process is illustrated in Figure 12-4?

ANS:
Translation (or protein synthesis) is illustrated.

PTS: 1 REF: p. 304

2. Interpreting Graphics Identify structure C in Figure 12-4.

ANS:
Structure C is a ribosome.

PTS: 1 REF: p. 304

3. Interpreting Graphics Which labeled structure in Figure 12-4 is a codon?

ANS:
Structure F is a codon.

PTS: 1 REF: p. 302

4. Inferring What is the relationship between the codons and anticodons in Figure 12-4? How is this relationship important?

ANS:
The codons and anticodons have complementary nitrogenous bases, allowing them to base pair. Since each tRNA carries only one kind of amino acid, the base pairing between the anticodons and codons brings a specific sequence of amino acids to the ribosomes.

PTS: 1 REF: p. 304

5. Predicting In Figure 12-4, what will happen after the ribosome joins the methionine and phenylalanine?

ANS:
The bond between the methionine and its tRNA will be broken. The tRNA will move away from the ribosome, allowing the ribosome to bind with another tRNA. The ribosome will move down the mRNA to the next codon.

PTS: 1 REF: p. 304