chapter 17

Which one of the following, if missing, would usually prevent translation from starting? a. AUG codon b. poly-A tail c. exon d. 5' cap

a. AUG codon

Codons are three-base sequences that specify the addition of a single amino acid. How do eukaryotic codons and prokaryotic codons compare? a. Codons are a nearly universal language among all organisms. b. The translation of codons is mediated by tRNAs in eukaryotes, but translation requires no intermediate molecules such as tRNAs in prokaryotes. c. Prokaryotic codons usually specify different amino acids than those of eukaryotes. d. Prokaryotic codons usually contain different bases than those of eukaryotes.

a. Codons are a nearly universal language among all organisms.

In the process of transcription, _____. a. RNA is synthesized b. proteins are synthesized c. DNA is replicated d. mRNA attaches to ribosomes

a. RNA is synthesized

The tRNA shown in the figure above has its 3' end projecting beyond its 5' end. What will occur at this 3' end? a. The amino acid binds covalently. b. The 5' cap of the mRNA will become covalently bound. c. The excess nucleotides (ACCA) will be cleaved off at the ribosome. d. The small and large subunits of the ribosome will attach to it.

a. The amino acid binds covalently.

A single base substitution mutation is least likely to be deleterious when the base change results in _____. a. a codon that specifies the same amino acid as the original codon b. a stop codon c. an amino acid substitution that alters the tertiary structure of the protein d. an amino acid substitution at the active site of an enzyme

a. a codon that specifies the same amino acid as the original codon

Which of the following occurs in prokaryotes but not in eukaryotes? a. concurrent transcription and translation b. gene regulation c. translation in the absence of a ribosome d. post-transcriptional splicing

a. concurrent transcription and translation

A nonsense mutation in a gene _____. a. introduces a premature stop codon into the mRNA b. has no effect on the amino acid sequence of the encoded protein c. alters the reading frame of the mRNA d. changes an amino acid in the encoded protein

a. introduces a premature stop codon into the mRNA

A primary transcript in the nucleus of a eukaryotic cell is _____ the functional mRNA, while a primary transcript in a prokaryotic cell is _____ the functional mRNA. a. larger than; the same size as b. the same size as; larger than c. the same size as; smaller than d. larger than; smaller than

a. larger than; the same size as

According to the central dogma, what molecule should go in the blank? DNA → _____ → Proteins a. mRNA b. mtDNA c. rRNA d. tRNA

a. mRNA

Translation requires _____. a. mRNA, tRNA, and rRNA b. mRNA, tRNA, DNA, and rRNA c. mRNA, DNA, and rRNA d. mRNA, tRNA, and DNA

a. mRNA, tRNA, and rRNA

Transcription in eukaryotes requires which of the following in addition to RNA polymerase? a. several transcription factors b. start and stop codons c. aminoacyl-tRNA synthetase d. ribosomes and tRNA

a. several transcription factors

The figure above shows a simple metabolic pathway. According to Beadle and Tatum's hypothesis, how many genes are necessary for this pathway? a. 3 b. 2 c. It cannot be determined from the pathway. d. 1

b. 2

A particular triplet of bases in the template strand of DNA is 5' AGT 3'. The corresponding codon for the mRNA transcribed is _____. a. 3' ACU 5' b. 3' UCA 5' c. 5' TCA 3' d. 3' UGA 5'

b. 3' UCA 5'

Which of the following does not occur in prokaryotic gene expression, but does occur in eukaryotic gene expression? a. RNA polymerase binds to the promoter. b. A cap is added to the 5' end of the mRNA. c. RNA polymerase requires a primer to elongate the molecule. d. mRNA, tRNA, and rRNA are transcribed.

b. A cap is added to the 5' end of the mRNA.

Which of the following contradicts the one-gene, one-enzyme hypothesis? a. Sickle-cell anemia results in defective hemoglobin. b. A single antibody gene can code for different related proteins, depending on the splicing that takes place post-transcriptionally. c. Alkaptonuria results when individuals lack a single enzyme involved in the catalysis of homogentisic acid. d. A mutation in a single gene can result in a defective protein.

b. A single antibody gene can code for different related proteins, depending on the splicing that takes place post-transcriptionally.

Refer to the figure above. What would the anticodon be for a tRNA that transports phenylalanine to a ribosome? a. TTT b. AAA c. CCC d. UUU

b. AAA

Which one of the following statements about RNA processing is true? a. A primary transcript is often much shorter than the final RNA molecule that leaves the nucleus. b. Ribozymes may function in RNA splicing. c. RNA splicing can be catalyzed by tRNA. d. Exons are cut out before mRNA leaves the nucleus.

b. Ribozymes may function in RNA splicing.

In an experimental situation, a student researcher inserts an mRNA molecule into a eukaryotic cell after she has removed its 5' cap and poly-A tail. Which of the following would you expect her to find? a. The mRNA is quickly converted into a ribosomal subunit. b. The molecule is digested by enzymes because it is not protected at the 5' end. c. The cell adds a new poly-A tail to the mRNA. d. The mRNA attaches to a ribosome and is translated, but more slowly.

b. The molecule is digested by enzymes because it is not protected at the 5' end.

The figure above represents tRNA that recognizes and binds a particular amino acid (in this instance, phenylalanine). Which codon on the mRNA strand codes for this amino acid? a. GUG b. UUC c. UGG d. GUA

b. UUC

Accuracy in the translation of mRNA into the primary structure of a polypeptide depends on specificity in the _____. a. binding of ribosomes to mRNA b. binding of the anticodon to the codon and the attachment of amino acids to tRNAs c. binding of the anticodon to small subunit of the ribosome d. attachment of amino acids to rRNAs

b. binding of the anticodon to the codon and the attachment of amino acids to tRNAs

A signal peptide _____. a. directs an mRNA molecule into the cisternal space of the ER b. helps target a protein to the ER c. signals the initiation of transcription d. terminates translation of messenger RNA

b. helps target a protein to the ER

A mutant bacterial cell has a defective aminoacyl-tRNA synthetase that attaches a lysine to tRNAs with the anticodon AAA instead of the normal phenylalanine. The consequence of this for the cell will be that _____. a. the cell will compensate for the defect by attaching phenylalanine to tRNAs with lysine-specifying anticodons b. proteins in the cell will include lysine instead of phenylalanine at amino acid positions specified by the codon UUU c. the ribosome will skip a codon every time a UUU is encountered d. none of the proteins in the cell will contain phenylalanine

b. proteins in the cell will include lysine instead of phenylalanine at amino acid positions specified by the codon UUU

Which one of the following, if missing, would usually prevent translation from starting? a. exon b. 5' cap c. AUG codon d. poly-A tail

c. AUG codon

Which of the following best describes the significance of the TATA box in eukaryotic promoters? a. It is the recognition site for ribosomal binding. b. Its significance has not yet been determined. c. It is the recognition site for a specific transcription factor. d. It sets the reading frame of the mRNA.

c. It is the recognition site for a specific transcription factor.

What must occur before a newly made polypeptide is secreted from a cell? a. It must be translated by a ribosome that remains free within the cytosol. b. Its signal sequence must be cleaved off before the polypeptide can enter the ER. c. Its signal sequence must target it to the ER, after which it goes to the Golgi. d. Its signal sequence must target it to the plasma membrane, where it causes exocytosis.

c. Its signal sequence must target it to the ER, after which it goes to the Golgi.

What does it mean when we say the genetic code is redundant? a. The genetic code is different for different domains of organisms. b. A single codon can specify the addition of more than one amino acid. c. More than one codon can specify the addition of the same amino acid. d. The genetic code is universal (the same for all organisms).

c. More than one codon can specify the addition of the same amino acid.

How might a single base substitution in the sequence of a gene affect the amino acid sequence of a protein encoded by the gene, and why? a. It is not possible for a single base substitution to affect protein structure, because each codon is three bases long. b. All amino acids following the substitution would be affected, because the reading frame would be shifted. c. Only a single amino acid could change, because the reading frame is unaffected. d. The amino acid sequence would be substantially altered, because the reading frame would change with a single base substitution.

c. Only a single amino acid could change, because the reading frame is unaffected.

Which of the following statements best describes the termination of transcription in prokaryotes? a. RNA polymerase transcribes through a stop codon, causing the polymerase to stop advancing through the gene and release the mRNA. b. Once transcription has initiated, RNA polymerase transcribes until it reaches the end of the chromosome. c. RNA polymerase transcribes through the terminator sequence, causing the polymerase to separate from the DNA and release the transcript. d. RNA polymerase transcribes through the polyadenylation signal, causing proteins to associate with the transcript and cut it free from the polymerase.

c. RNA polymerase transcribes through the terminator sequence, causing the polymerase to separate from the DNA and release the transcript.

Of the following, which is the most current description of a gene? a. a DNA subunit that codes for a single complete protein b. a discrete unit of hereditary information that consists of a sequence of amino acids c. a DNA sequence that is expressed to form a functional product: either RNA or polypeptide d. a unit of heredity that causes formation of a phenotypic characteristic

c. a DNA sequence that is expressed to form a functional product: either RNA or polypeptide

The most commonly occurring mutation in people with cystic fibrosis is a deletion of a single codon. This results in _____. a. a frameshift mutation b. a nonsense mutation c. a polypeptide missing an amino acid d. a base-pair substitution

c. a polypeptide missing an amino acid

A ribozyme is _____. a. an enzyme that synthesizes RNA as part of the transcription process b. a catalyst that uses RNA as a substrate c. an RNA with catalytic activity d. an enzyme that catalyzes the association between the large and small ribosomal subunits

c. an RNA with catalytic activity

Alternative RNA splicing _____. a. increases the rate of transcription b. can allow the production of similar proteins from different RNAs c. can allow the production of proteins of different sizes and functions from a single mRNA d. is a mechanism for increasing the rate of translation

c. can allow the production of proteins of different sizes and functions from a single mRNA

An original section of DNA has the base sequence AGCGTTACCGT. A mutation in this DNA strand results in the base sequence AGGCGTTACCGT. This change represents _____. a. a point mutation b. a silent mutation c. frameshift mutation d. a missense mutation

c. frameshift mutation

Garrod hypothesized that "inborn errors of metabolism" such as alkaptonuria occur because _____. a. enzymes are made of DNA, and affected individuals lack DNA polymerase b. metabolic enzymes require vitamin cofactors, and affected individuals have significant nutritional deficiencies c. genes dictate the production of specific enzymes, and affected individuals have genetic defects that cause them to lack certain enzymes d. certain metabolic reactions are carried out by ribozymes, and affected individuals lack key splicing factors

c. genes dictate the production of specific enzymes, and affected individuals have genetic defects that cause them to lack certain enzymes

Refer to the metabolic pathway illustrated above. If A, B, and C are all required for growth, a strain mutant for the gene-encoding enzyme B would be able to grow on medium supplemented with _____. a. nutrients A and C b. nutrient B only c. nutrient C only d. nutrient A only

c. nutrient C only

A part of an mRNA molecule with the following sequence is being read by a ribosome: 5' CCG-ACG 3'(mRNA). The following charged transfer RNA molecules (with their anticodons shown in the 3' to 5' direction) are available. Two of them can correctly match the mRNA so that a dipeptide can form. a. alanine-alanine b. cysteine-alanine c. proline-threonine d. glycine-cysteine

c. proline-threonine

Once a peptide has been formed between the amino acid attached to the tRNA in the P site and the amino acid associated with the tRNA in the A site, what occurs next? a. The codon-anticodon hydrogen bonds holding the tRNA in the A site are broken. b. reading of the next codon of mRNA c. translocation d. initiation

c. translocation

The genetic code is essentially the same for all organisms. From this, one can logically assume which of the following? a. The same codons in different organisms translate into different amino acids. b. Different organisms have different types of amino acids. c. DNA was the first genetic material. d. A gene from an organism can theoretically be expressed by any other organism.

d. A gene from an organism can theoretically be expressed by any other organism.

During elongation, which site in the ribosome represents the location where a codon is being read? a. P site b. the small ribosomal subunit c. E site d. A site

d. A site

Which one of the following statements about RNA processing is true? a. RNA splicing can be catalyzed by tRNA. b. A primary transcript is often much shorter than the final RNA molecule that leaves the nucleus. c. Exons are cut out before mRNA leaves the nucleus. d. Ribozymes may function in RNA splicing.

d. Ribozymes may function in RNA splicing.

Accuracy in the translation of mRNA into the primary structure of a polypeptide depends on specificity in the _____. a. attachment of amino acids to rRNAs b. binding of ribosomes to mRNA c. binding of the anticodon to small subunit of the ribosome d. binding of the anticodon to the codon and the attachment of amino acids to tRNAs

d. binding of the anticodon to the codon and the attachment of amino acids to tRNAs

The release factor (RF) _____. a. releases the ribosome from the ER to allow polypeptides into the cytosol b. supplies a source of energy for termination of translation c. releases the amino acid from its tRNA to allow the amino acid to form a peptide bond d. binds to the stop codon in the A site in place of a tRNA

d. binds to the stop codon in the A site in place of a tRNA

What type of bonding is responsible for maintaining the shape of the tRNA molecule shown in the figure above? a. peptide bonding between amino acids b. van der Waals interactions between hydrogen atoms c. ionic bonding between phosphates d. hydrogen bonding between base pairs

d. hydrogen bonding between base pairs

Codons are part of the molecular structure of _____. a. tRNA b. a protein c. rRNA d. mRNA

d. mRNA

There are sixty-one mRNA codons that specify an amino acid, but only forty-five tRNAs. This is best explained by the fact that _____. a. some tRNAs have anticodons that recognize four or more different codons b. the DNA codes for all sixty-one tRNAs, but some are then destroyed c. many codons are never used, so the tRNAs that recognize them are dispensable d. the rules for base pairing between the third base of a codon and tRNA are flexible

d. the rules for base pairing between the third base of a codon and tRNA are flexible