Mastering Biology 9 TRNAs

Where does translation take place?

 a) Endoplasmic reticulum b) Ribosome c) Golgi apparatus d) Nucleus

Answer: b) Ribosome

Which nucleic acid is translated to make a protein?

 a) DNA b) rRNA c) tRNA d) mRNA

Answer: d) mRNA

Which of the following processes is an example of a post-translational modification? 

a) Initiation b) Peptide bond formation c) Phosphorylation d) Elongation

Answer: c) Phosphorylation

Which of the following steps occurs last in the initiation phase of translation? 

a) The small subunit of the ribosome binds to the 5′ cap on the mRNA. b) The large ribosomal subunit joins the complex. c) An aminoacyl tRNA binds to the start codon. d) A peptide bond is formed between two adjacent amino acids.

Answer: b) The large ribosomal subunit joins the complex.

At which site do new aminoacyl tRNAs enter the ribosome during elongation?

 a) B-site b) A-site c) P-site d) E-site

Answer: b) A-site

What is meant by translocation?

 a) The polypeptide chain grows by one amino acid. b) The ribosome slides one codon down the mRNA. c) The two ribosomal subunits are joined in a complex. d) The completed polypeptide is released from the ribosome.

Answer: b) The ribosome slides one codon down the mRNA.

True or false. A tRNA with an anticodon complementary to the stop codon catalyzes the reaction by which translation is terminated

 a) True b) False

Answer: b) False

What enzyme catalyzes the attachment of an amino acid to tRNA?

 a) aminoacyl-tRNA synthetase b) rubisco c) dextrinase d) argininosuccinate lyase e) nuclease

Answer: a) aminoacyl-tRNA synthetase

The tRNA anticodon, GAC, is complementary to the mRNA codon with the sequence _____. 

a) CAG b) CTG c) GAC d) CUG e) TCG

Answer: d) CUG

The initiator tRNA attaches at the ribosome’s _____ site. 

a) A b) translocation c) E d) P e) Q

Answer: d) P

Which one of the following is true of tRNAs? 

a) tRNAs are double-stranded. b) Each tRNA binds a particular amino acid. c) There are four types of tRNA. d) tRNAs carry special sequences known as codons. e) All of the above

Answer: b) Each tRNA binds a particular amino acid.

How is translation initiated? 

a) The small ribosomal subunit binds to the mRNA. 

b) The tRNA bearing methionine binds to the start codon.

c) The large ribosomal subunit binds to the small one. 

d) The start codon signals the start of translation. e) All of the above.

Answer: e) All of the above

A particular triplet of bases in the coding sequence of DNA is AAA. The anticodon on the tRNA that binds the mRNA codon is a) UUA. b) UUU. c) AAA. d) TTT. e) either UAA or TAA, depending on first base wobble.

Answer: b) UUU

Accuracy in the translation of mRNA into the primary structure of a polypeptide depends on specificity in the 

a) bonding of the anticodon to the codon and the attachment of amino acids to tRNAs. 

b) bonding of the anticodon to the codon. 

c) binding of ribosomes to mRNA. 

d) attachment of amino acids to tRNAs. 

e) shape of the A and P sites of ribosomes.

Answer: a) bonding of the anticodon to the codon and the attachment of amino acids to tRNAs 

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 ribosome will skip a codon every time a UUU is encountered. b) proteins in the cell will include lysine instead of phenylalanine at amino acid positions specified by the codon UUU. c) none of the options will occur; the cell will recognize the error and destroy the tRNA. d) the cell will compensate for the defect by attaching phenylalanine to tRNAs with lysine-specifying anticodons. e) none of the proteins in the cell will contain phenylalanine.

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

When the ribosome reaches a stop codon on the mRNA, no corresponding tRNA enters the A site. If the translation reaction were to be experimentally stopped at this point, which of the following would you be able to isolate? 

a) an assembled ribosome with a polypeptide attached to the tRNA in the P site b) separated ribosomal subunits, a polypeptide, and free tRNA c) separated ribosomal subunits with a polypeptide attached to the tRNA d) a cell with fewer ribosomes e) an assembled ribosome with a separated polypeptide

Answer: a) an assembled ribosome with a polypeptide attached to the tRNA in the P site

Use the following information to answer the question.A transfer RNA (#1) attached to the amino acid lysine enters the ribosome. The lysine binds to the growing polypeptide on the other tRNA (#2) in the ribosome already.

Answer: c) E site

True or false? A codon is a group of three bases that can specify more than one amino acid. a) True b) False

Answer: b) False

Which of the following statements about mutations is false? 

a) A deletion mutation results in the loss of a base in the DNA sequence. b) A knock-out mutation results in a total absence of the mutated protein. c) Addition and deletion mutations disrupt the primary structure of proteins. d) An addition mutation results in an added base in the DNA sequence.

Answer: b) A knock-out mutation results in a total absence of the mutated protein.

If a DNA sequence is altered from TAGCTGA to TAGTGA, what kind of mutation has occurred?

 a) Both addition and deletion. b) Deletion. c) None. d) Addition.

Answer: b) Deletion

Which mutation(s) would not change the remainder of the reading frame of a gene sequence that follows the mutation(s)? 

a) One addition and two deletion mutations. b) One addition mutation. c) One deletion mutation. d) One addition and one deletion mutation.

Answer: d) One addition and one deletion mutation.

If the sequence ATGCATGTCAATTGA were mutated such that a base were inserted after the first G and the third T were deleted, how many amino acids would be changed in the mutant protein? 

a) One. b) None. c) Three. d) Two.

Answer: d) Two

If a mutated DNA sequence produces a protein that differs in one central amino acid from the normal protein, which of the following kinds of mutations could have occurred? 

a) An addition mutation and a deletion mutation. b) An addition mutation c) A deletion mutation. d) None.

Answer: a) An addition mutation and a deletion mutation.

Which of the following types of mutation, resulting in an error in the mRNA just after the AUG start of translation, is likely to have the most serious effect on the polypeptide product?

 a) a deletion of a codon b) a substitution of the third nucleotide in an ACC codon c) a deletion of 2 nucleotides d) a substitution of the first nucleotide of a GGG codon e) an insertion of a codon

Answer: c) a deletion of 2 nucleotides

What is the effect of a nonsense mutation in a gene? 

a) It changes an amino acid in the encoded protein. b) It alters the reading frame of the mRNA. c) It introduces a premature stop codon into the mRNA. d) It has no effect on the amino acid sequence of the encoded protein. e) It prevents introns from being excised.

Answer: c) It introduces a premature stop codon into the mRNA.

A frameshift mutation could result from 

a) a base deletion only. b) either an insertion or a deletion of a base. c) a base insertion only. d) deletion of three consecutive bases. e) a base substitution only.

Answer: b) either an insertion or a deletion of a base.

Which of the following DNA mutations is the most likely to be damaging to the protein it specifies? 

a) a point mutation b) a codon deletion c) a codon substitution d) a base-pair deletion e) a substitution in the last base of a codon

Answer: d) a base-pair deletion

Of the following, which is the most current description of a gene?

a) a DNA – RNA sequence combination that results in an enzymatic product b) a discrete unit of hereditary information that consists of a sequence of amino acids c) a unit of heredity that causes formation of a phenotypic characteristic d) a DNA sequence that is expressed to form a functional product: either RNA or polypeptide e) a DNA subunit that codes for a single complete protein

Answer: d) a DNA sequence that is expressed to form a functional product: either RNA or polypeptide

In eukaryotic cells, transcription cannot begin until 

a) several transcription factors have bound to the promoter. b) the two DNA strands have completely separated and exposed the promoter. c) the 5′ caps are removed from the mRNA. d) the DNA introns are removed from the template. e) DNA nucleases have isolated 

the transcription unit.

Answer: a) several transcription factors have bound to the promoter.

Muscle cells differ from nerve cells mainly because they 

a) have unique ribosomes. b) have different chromosomes. c) use different genetic codes. d) contain different genes. e) express different genes.

Answer: e) express different genes.

Some forms of chromatin modification can be passed on to future generations of cells. 

a) true b) false

Answer: a) true

Acetylation of histone tails in chromatin allows access to DNA for transcription. 

a) true b) false

Answer: a) true

Deacetylation of histone tails in chromatin loosens the association between nucleosomes and DNA. a) true b) false

Answer: b) false

Methylation of histone tails in chromatin can promote condensation of the chromatin.

 a) true b) false

Answer: a) true

Acetylation of histone tails is a reversible process

 a) true b) false

Answer: a) true

DNA is not transcribed when chromatin is packaged tightly in a condensed form

 a) true b) false

Answer: a) true

_____ bind(s) to DNA enhancer regions.

 a) RNA polymerase b) Promoters c) Introns d) Activators e) Exons

Answer: d) Activators

Which of the following terms describes the DNA-protein complexes that look like beads on a string? 

a) 30-nanometer fiber b) Histones c) Nucleosome d) Chromatin

Answer: c) Nucleosome

Which of the following regulatory elements is not composed of DNA sequences? 

a) Silencers b) Enhancers c) Activators d) Promoter-proximal elements

Answer: c) Activators

True or false? Regulatory and basal transcription factors regulate transcription by binding to the promoter. 

a) True b) False

Answer: b) False

Which of the following regulatory DNA sequences might be located thousands of nucleotides away from the transcription start site of a gene? 

a) Enhancer b) Promoter c) TATA box d) Promoter-proximal element

Answer: a) Enhancer

Which of the following events in transcription initiation likely occurs last? 

a) Basal transcription factors form a basal transcription complex. b) TBP is recruited to the promoter. c) Regulatory transcription factors bind to enhancers. d) RNA polymerase binds to the promoter of the gene.

Answer: d) RNA polymerase binds to the promoter of the gene.

True or false? One possible way to alter chromatin structure such that genes could be transcribed would be to make histone proteins more positively charged. 

a) True b) False

Answer: b) False

In humans, the hormone testosterone enters cells and binds to specific proteins, which in turn bind to specific sites on the cells’ DNA. These proteins probably act to do what?

 a) alter the pattern of DNA splicing b) promote recombination c) help RNA polymerase transcribe certain genes d) unwind the DNA so that its genes can be transcribed e) cause mutations in the DNA

Answer: c) help RNA polymerase transcribe certain genes

Two potential devices that eukaryotic cells use to regulate transcription are

 a) DNA acetylation and methylation. b) histone amplification and DNA acetylation. c) DNA methylation and histone modification. d) DNA amplification and histone methylation. e) DNA methylation and histone amplification.

Answer: c) DNA methylation and histone modification

In eukaryotes, general transcription factors 

a) are required for the expression of specific protein-encoding genes. b) bind to other proteins or to a sequence element within the promoter called the TATA box. c) usually lead to a high level of transcription even without additional specific transcription factors. d) inhibit RNA polymerase binding to the promoter and begin transcribing. e) bind to sequences just after the start site of transcription

Answer: b) bind to other proteins or to a sequence element within the promoter called the TATA box.

Transcription factors in eukaryotes usually have DNA binding domains as well as other domains that are also specific for binding. In general, which of the following would you expect many of them to be able to bind? 

a) protein-based hormones b) repressors c) tRNA d) ATP e) other transcription factors

Answer: e) other transcription factors

miRNAs can control gene expression by what action?

a) degrading proteins as soon as they are formed b) inhibiting the catalytic activity of rRNA c) binding to mRNAs and degrading them or blocking their translation d) seeking out viral DNA and destroying it e) binding to DNA and preventing transcription of certain genes

Answer: c) binding to mRNAs and degrading them or blocking their translation

The phenomenon in which RNA molecules in a cell are destroyed if they have a sequence complementary to an introduced double-stranded RNA is called 

a) RNA obstruction. b) RNA interference. c) RNA targeting. d) RNA disposal. e) RNA blocking.

Answer: b) RNA interference