Ch9 The Chemistry of Heredity and Gene Test Bank + Answers

Chapter 9: The Chemistry of Heredity and Gene Expression

Multiple-Choice Questions

The pyrimidine bases of DNA are:

a. cytosine and thymine.

b. cytosine and adenine.

c. adenine and guanine.

d. guanine and cytosine.

e. guanine and thymine.

Data obtained by Erwin Chargaff indicated that in DNA the ratio of nucleotides containing _________ to those containing _______ is approximately 1:1.

a. adenine; cytosine

b. adenine; thymine

c. guanine; thymine

d. thymine; cytosine

e. guanine; adenine

The DNA molecule has the shape of a:

a. single helix.

b. double helix

c. triple helix.

d. step ladder.

e. staircase.

In the ladder analogy of DNA structure, the sides of the ladder are composed of:

a. sugars.

b. phosphates.

c. alternating sugars and phosphates.

d. alternating sugars and nitrogenous bases.

e. nitrogenous bases.

In a DNA molecule, the hydrogen bonds join:

a. the paired nitrogenous bases.

b. sugars and phosphates.

c. sugars and nitrogenous bases.

d. phosphates and nitrogenous bases.

e. pairs of sugars.

Which of the following are complementary bases?

a. adenine and cytosine

b. adenine and guanine

c. thymine and cytosine

d. guanine and cytosine

e. thymine and guanine

Each strand in a DNA molecule:

a. is bonded to two other strands.

b. has a 5′ end and a 3′ end.

c. has two 5′ ends.

d. has two 3′ ends.

e. is parallel to the other strand(s) but not antiparallel.

Which of the following statements about DNA replication in eukaryotes is FALSE?

a. It is a bidirectional process.

b. Helicases break the hydrogen bonds at the origin of replication.

c. DNA polymerases catalyze the synthesis of the new strands.

d. The two replication forks move in opposite directions away from the origin.

e. There is only one origin of replication.

After a DNA molecule “unzips,” the two strands are kept separated by:

a. single-strand binding proteins.

b. DNA polymerase.

c. DNA ligase.

d. helicases.

e. telomerase.

DNA replication requires a short strand of _____ as a primer to initiate synthesis.

a. carbohydrates

b. amino acids

c. phospholipids

d. RNA

e. magnesium ions

In DNA replication, the lagging strand differs from the leading strand in that the lagging strand is synthesized:

a. in a 5′ to 3′ direction.

b. in a 3′ to 5′ direction.

c. in fragments.

d. using DNA polymerase.

e. outside the replication bubble.

In DNA replication, _______ catalyzes the joining of Okazaki fragments.

a. single-strand binding protein

b. DNA ligase

c. histone

d. DNA polymerase

e. helicase

RNA contains ______ instead of the ______ found in DNA.

a. adenine; thymine

b. uracil; thymine

c. adenine; uracil

d. guanine; cytosine

e. uracil; guanine

The role of ______ is to carry amino acids to the ribosomes.

a. DNA

b. mRNA

c. tRNA

d. rRNA

e. protein

The process of translation results in the synthesis of:

a. DNA.

b. mRNA.

c. tRNA.

d. rRNA.

e. protein.

A codon consists of _____ nucleotides in a(n) ____ molecule.

a. two; DNA

b. three; DNA

c. four; DNA

d. three; RNA

e. four; RNA

When scientists describe the genetic code as redundant, they mean that:

a. it becomes disorganized over time.

b. many amino acids have more than one codon.

c. some codons specify stop signals.

d. it varies with cell type.

e. it varies among species.

Which of the following statements about promoters is FALSE?

a. They are specific nucleotide sequences of DNA.

b. They consist of three nucleotides that bind to a codon.

c. They determine the position where RNA synthesis begins.

d. They determine which DNA strand is used as a template.

e. They are binding sites for RNA polymerase.

Which of the following molecules contains an anticodon?

a. DNA

b. mRNA

c. tRNA

d. rRNA

e. protein

A transfer RNA molecule carries a(n) ______ to the ribosomes.

a. amino acid

b. protein

c. mRNA molecule

d. ATP molecule

e. segment of DNA nucleotides

An aminoacyl-tRNA synthetase catalyzes the:

a. attachment of a particular tRNA to mRNA.

b. binding of RNA polymerase to the terminator.

c. binding of RNA polymerase to the promoter.

d. attachment of a particular amino acid to a particular tRNA.

e. attachment of a particular tRNA to the ribosome.

A ribosome consists of ______ and ______.

a. DNA; mRNA

b. mRNA; protein

c. mRNA; tRNA

d. rRNA; mRNA

e. rRNA; protein

An incoming aminoacyl-tRNA molecule binds to the ribosome at the ______ site.

a. A (aminoacyl)

b. mRNA-binding

c. P (peptidyl)

d. E (exit)

e. promoter

Which of the following events is NOT part of the initiation stage of translation?

a. The smaller ribosomal subunit attaches to mRNA.

b. GTP is hydrolyzed.

c. The larger ribosomal subunit attaches to the smaller subunit.

d. fMet-tRNA binds at the P site.

e. The initiator tRNA is released from the E site.

During the elongation stage of translation:

a. the two ribosomal subunits separate.

b. a polysome forms.

c. release factors bind at the A site.

d. fMet-tRNA binds to the initiation codon.

e. a peptide bond is formed.

Which of the following events is NOT part of the termination stage of translation?

a. The ribosome encounters a stop codon.

b. Release factors bind at the A site.

c. The ribosome moves along the mRNA to the next codon.

d. The ribosomal subunits separate.

e. The polypeptide chain is released.

Polypeptides destined for membranes of the Golgi complex are synthesized on ribosomes:

a. that are free in the cytosol.

b. attached to the endoplasmic reticulum.

c. in the nucleus.

d. in mitochondria.

e. in plastids.

In a cell of a multicellular organism:

a. all enzymes are expressed continuously.

b. some genes are expressed continuously.

c. some genes are not expressed.

d. some genes are switched “on” at certain times.

e. some genes are switched “off” at certain times.

Euchromatin differs from heterochromatin in that euchromatin:

a. stains more strongly.

b. is more tightly condensed.

c. predominates in centromeres.

d. predominates in telomeres.

e. is more readily transcribed during interphase.

Which of the following statements concerning telomeres is FALSE?

a. They consist of simple-sequence repeated DNA.

b. They are located at the ends of the chromosomes.

c. They serve as caps.

d. They are regions of active transcription.

e. They protect the chromosome from degradation.

Which of the following is the most likely next step after histones are acetylated?

a. DNA binds histones.

b. Translation is inhibited.

c. Translation occurs.

d. Transcription is inhibited.

e. Transcription occurs.

Acetyltransferases catalyze the attachment of acetyl groups to:

a. DNA.

b. ribosomes.

c. histones.

d. mRNA.

e. tRNA.

When DNA is methylated:

a. transcription is repressed.

b. transcription is stimulated.

c. histone tails bind DNA.

d. histone tails are released from DNA.

e. histones are acetylated.

Which of the following is the best estimate for the percentage of DNA in eukaryotic cells that codes for proteins?

a. less than 1 percent

b. less than 10 percent

c. about 25 percent

d. about 50 percent

e. about 75 percent

Interspersed repeated DNA units:

a. are arranged in tandem.

b. tend to be smaller than 10 base pairs long.

c. constitute less than 10 percent of the DNA of most multicellular organisms.

d. are identical to one another.

e. are believed to have originated from transposons.

Which of the following statements about simple-sequence repeated DNA segments is FALSE?

a. They are tandemly repeated.

b. They occur in telomeres.

c. They are dispersed throughout the DNA.

d. They occur in centromeres.

e. They have fewer than 10 base pairs.

Which of the following statements concerning transposons is FALSE?

a. They are “molecular parasites.”

b. They replicate more slowly than other genes.

c. They can be inserted into host genes.

d. Eukaryotes have epigenetic mechanisms for silencing them.

e. They can increase in number from one cell generation to the next.

Exons are segments of a gene that:

a. are transcribed into segments of mRNA that are snipped out before translation.

b. occur in prokaryotic but not eukaryotic chromosomes.

c. consist of RNA rather than DNA nucleotides.

d. are not transcribed by RNA polymerase.

e. are translated into protein.

Which of the following events occurs in eukaryotic cells but NOT in prokaryotic cells?

a. RNA polymerase attaches to a particular nucleotide sequence on the DNA.

b. RNA is synthesized using the 3′ to 5′ DNA strand as a template.

c. Two or more structural genes are transcribed onto a single RNA molecule.

d. mRNA transcripts are extensively modified before they leave the nucleus.

e. tRNAs, rRNAs, and mRNAs are all involved in the translation process.

Which of the following events is NOT involved in mRNA processing?

a. the addition of a 5′ “cap”

b. the addition of a poly-A tail

c. the forming of peptide bonds

d. the splicing together of exons

e. the removal of introns

Which of the following statements concerning noncoding RNAs is FALSE?

a. They are types of tRNA molecules.

b. They are present in most eukaryotic genomes.

c. Some are responsible for striking developmental abnormalities.

d. An example is microRNA.

e. Some are responsible for RNA interference.

True-False Questions

In the ladder molecule of a DNA molecule, the purine and pyrimidine bases comprise the sides of the ladder.

The complementarity of the two strands of DNA is a direct result of A pairing only with T and C pairing only with G.

The two strands of a DNA molecule are said to be antiparallel, each strand having its 5′ end at the same end of the molecule.

The “primer” that initiates DNA replication is composed of RNA.

DNA polymerase synthesizes new DNA strands only in the 5′ to 3′ direction.

In DNA replication, the leading strand is synthesized in fragments, called Okazaki fragments, while the lagging strand is synthesized continuously.

RNA contains thymine instead of uracil.

The genetic code in prokaryotes is different from that in eukaryotic cells.

The function of aminoacyl-tRNA synthetase is to catalyze the synthesis of tRNA.

The incoming amino-acid-bearing tRNA binds at the A site.

Peptide bond formation on the ribosome is catalyzed by RNA.

In a plant, root cells have the same genetic composition as leaf cells.

Heterochromatin is more tightly condensed than euchromatin and in some regions is never transcribed.

Histone acetylation neutralizes the histone tails, and consequently transcription is repressed.

When DNA is methylated, transcription is stimulated.

Epigenetic inheritance refers to the inheritance of traits encoded by genes in the telomeres.

The two major categories of repeated DNA are tandemly repeated DNA and interspersed repeated DNA.

Simple-sequence repeated DNA occurs throughout the genome except at the centromeres and telomeres.

The most abundant interspersed repeat sequences are transposons.

Exons are noncoding sequences of nucleotides that are present in genes.

Most eukaryotic structural genes contain introns.

The 5′ cap of mRNA serves to bind the mRNA molecule to the ribosome.

Before transcription is completed, a poly-A tail is added to the 3′ end of the mRNA.

An example of a noncoding RNA is tRNA.

MicroRNAs are responsible for RNA interference.

Essay Questions

1. The Structure of DNA; p. 175; moderate

Explain the correlation between Chargaff’s data on nucleotide ratios and Watson and Crick’s concept of complementary base-pairing.

2. The Structure of DNA; p. 175; easy

Use the ladder model to describe the structure of DNA.

3. DNA Replication; pp. 177–178; moderate

Summarize the main steps in DNA replication. Why is the lagging strand synthesized in fragments rather than as a continuous strand?

4. From DNA to Protein: The Role of RNA; p. 179; easy

How do RNA and DNA differ? How are they similar?

5. The Genetic Code; p. 180; easy

Explain why at least three nucleotides must specify each amino acid.

6. Protein Synthesis; p. 181; difficult

Why is the specificity of aminoacyl-tRNA synthetases essential for the synthesis of proteins? What would be the consequences for the cell if a particular aminoacyl-tRNA synthetase was not specific for a particular amino acid?

7. Protein Synthesis; pp. 181–184; moderate

Summarize the main events occurring in translation.

8. Regulation of Gene Expression in Eukaryotes; p. 186; moderate

Explain the concept of totipotency as it applies to plant cells.

9. Regulation of Gene Expression in Eukaryotes; p. 186; moderate

Explain the difference between euchromatin and heterochromatin. What role do they play in gene regulation?

10. Regulation of Gene Expression in Eukaryotes; p. 186; easy

Compare and contrast the effects of histone acetylation and DNA methylation.

11. Regulation of Gene Expression in Eukaryotes; pp. 186–187; difficult

What are some of the roles played by specific proteins in regulating the transcription of genes?

12. The DNA of the Eukaryotic Chromosome; p. 187; moderate

Explain the differences between tandemly repeated DNA and interspersed repeated DNA.

13. The DNA of the Eukaryotic Chromosome; p. 187; moderate

What are introns and exons, and how do they differ from structural genes?

14. Transcription and Processing of mRNA in Eukaryotes; pp. 188–189; moderate

Discuss the main types of mRNA processing in eukaryotes. How is this different from mRNA processing in prokaryotes?

15. Noncoding RNAs and Gene Regulation; p. 190; moderate

Explain what is meant by a “noncoding RNA.” Describe how noncoding RNAs are involved in RNA interference.