Chapter 14- Gene Expression
A particular triplet of bases in the template strand of DNA is 5'-AGT-3'. The corresponding codon for the mRNA transcribed is
3'-UCA-5'
What is the function of GTP in translation?
GTP provides the energy for the formation of the initiation complex, using initiation factors.
The "universal" genetic code is now known to have exceptions. Evidence for this can be found if which of the following is true?
If UGA, usually a stop codon, is found to code for an amino acid such as tryptophan, (usually coded for by UGG only)
What is the effect of a nucleotide pair substitution that results in a nonsense mutation in a gene?
It introduces a premature stop codon into the mRNA
In what way might a point mutation in DNA make a difference in the function of a protein?
It might substitute a different amino acid in the active site
What must happen to a newly made polypeptide before it can be secreted from a cell?
Its signal sequence must be target it to the ER, after which it goes to the golgi
Suppose that an error in transcription alters the formation of a single tRNA molecule in a cell. The altered tRNA still attaches to the same amino acid (Phe), but its anticodon loop has the sequence AAU, which binds to the mRNA codon UUA (usually specifying the amino acid leucine, Leu). What will be the effect on the translocation of polypeptides in this cell?
One altered tRNA molecule will have little effect because it will compete with many "normal" ones
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. What would be a potential consequence for a cell in which this happens? Remember that phenylalanine may be encoded by multiple codons.
Proteins in the cell will include lysine instead of phenylalanine at amino acid positions specified by the codon UUU
During splicing, which molecular component of the spliceosome catalyzes the excision reaction?
RNA
In eukaryotes there are several different types of RNA polymerase. Which type is involved in the transcription of mRNA known as pre-mRNA?
RNA polymerase II
Which of the following experimental procedures is most likely to speed up mRNA degradation in a eukaryotic cell?
Removal of the 5' cap
A particular triplet of bases in the coding sequence of DNA is AAA. The anticodon of the tRNA that binds the mRNA codon is
UUU
Which of the following DNA mutations is likely to have the most negative effect on the protein it specifies?
a base-pair deletion
When the spliceosome binds to elements of this structure, where can it attach?
a certain sequence along the intron
Which of the following types of mutation, resulting in an error in the mRNA just after the 3' AUG start codon, is likely to have the most serious effect on the polypeptide product?
a deletion of two nucleotides
Which of the following does not occur in prokaryotic gene expression, but does occur in eukaryotic gene expression?
a poly-A tail is added to the 3' end of an mRNA and a cap is added to the 5' end
Which of the following mutations is most likely to cause a phenotypic change?
a single nucleotide deletion in an exon coding for an active site of a protein
What is a ribozyme?
an RNA with enzymatic activity
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 from the cell?
an assembled ribosome with a polypeptide attached to the tRNA in the P site
Accuracy in the translation of mRNA into the sequence of amino acids in a polypeptide depends on specificity in which of the following?
bonding of the anticodon to the codon and the attachment of amino acids to tRNAs
Which of the following types of mutations could result in a frameshift mutation?
either an insertion or deletion of a base
What type of bonding is responsible for maintaining the shape of the tRNA molecule?
hydrogen bonding between base pairs
Which of the following is a function of a poly-A tail in mRNA?
it is a sequence that codes for the binding of RNA polymerase to the DNA
Garrod hypothesized that inherited diseases such as alkaptonuria, the inability to metabolize the chemical alkapton, occur because
metabolic enzymes require vitamin cofactors, and affected individuals have significant nutritional deficiencies
The process of translation in both prokaryotes and eukaryotes requires tRNAs, amino acids, and ribosomal subunits. Which of the following components must also be present for translation to proceed?
protein factors and GTP
Transcription in eukaryotes requires which of the following in addition to RNA polymerase?
several transcription factors
In comparing DNA replication with RNA transcription in the same cell, which of the following is only true of replication
the entire template molecule is represented in the product
Which of the following statements is true about protein synthesis in prokaryotes?
translation can begin while transcription is still in progress
RNA polymerase moves in which direction along DNA?
3' to 5' along the template strand
Of the following, which is the most current description of a gene?
A DNA sequence that is expressed to form a functional product: either RNA or polypeptide
The nitrogenous base adenine is found in all members of which of the following groups of molecules?
ATP, RNA, and DNA
Which of the following statements correctly describes the function of a signal peptide?
It assists in the translocation of polypeptides across the ER membrane
What is the function of the release factor in translation?
It binds to the stop codon in the A site in place of tRNA
which of the following statements correctly describes alternative RNA splicing?
It can allow the production of proteins of different sizes and functions from a single mRNA
RNA polymerase in a prokaryote is composed of several subunits. Most of these subunits are the same for transcription of any gene, but one, known as sigma, varies considerably. Which of the following is the most probable advantage for the organism in having such variability in RNA polymerase?
It might allow the polymerase to recognize different promoters under certain environmental conditions
Garrod's information about the enzyme alteration resulting in alkaptonuria led to further elucidation of the same pathway in humans. Phenylketonuria (PKU) occurs when another enzyme in the pathway is altered or missing, resulting in a failure of phenylalanine (phe) to be metabolized to another amino acid: tyrosine. Tyrosine is an earlier substrate in the pathway altered in alkaptonuria. How might PKU affect the presence or absence of alkaptonuria?
It would have no effect because tyrosine is also available from the diet
Which of the following statements best describes the termination of transcription in prokaryotes?
RNA polymerase transcribes through the terminator sequence, causing the polymerase to separate from the DNA and release the transcript
An experimenter has altered the 3' end of the tRNA corresponding to the amino acid methionine in such a way as to remove the 3' AC. Which of the following statements correctly describes the most likely result of this change?
The amino acid methionine will not be covalently bound to the altered tRNA
In an experimental situation, a student researcher inserts an mRNA molecule into a eukaryotic cell after he has removed its 5' cap and poly-A tail. Which of the following would you expect him to find?
The molecule is degraded by hydrolytic enzymes because it is no longer protected at the 5' end and the 3' end
In order for a eukaryotic gene to be engineered into a bacterial colony to be expressed, what must be included in addition to the coding exons of the gene?
a bacterial promoter sequence
Which small-scale mutation would be most likely to have the greatest negative effect on the functioning of a protein?
a base deletion near the start of the gene
The genetic code is essentially the same for all organisms. Based on this information, one can logically assume which of the following statements to be correct?
a gene from an organism can theoretically be expressed by any other organism
The most commonly occurring mutation in people with cystic fibrosis is a deletion of a single codon. What is the most likely result of this mutation in the protein product
a polypeptide missing an amino acid
When translating secretory or membrane proteins, ribosomes are directed to the ER membrane by
a signal-recognition particle that brings ribosomes to a receptor protein in the ER membrane
Which of the following descriptions of nucleotide triplets best represents a codon?
a triplet in the same reading frame as an upstream AUG
A part of the promoter called the TATA box, is said to be highly conserved in evolution. Which of the following might this illustrate?
any mutation in the sequence is selected against
Which of the following best describes the significance of the TATA box in eukaryotic promoters?
it is the recognition site for a specific transcription factor
A eukaryotic transcription unit that is 8,000 nucleotides ling may use 1,200 nucleotides to make a protein consisting of approximately 400 amino acids. This is best explained by the fact that
many noncoding stretches of nucleotides are present in eukaryotic DNA
What will occur at the 3' end of a tRNA molecule with the 3' end extending beyond the 5' end?
the amino acid will bing covalently
There are 61 mRNA codons that specify an amino acid, but only 45 tRNAs. This is best explained by the fact that
the rules for base pairing between the third base of a codon a tRNA are flexible
Which of the following events in translation is the first to occur in eukaryotes?
the small subunit of the ribosome recognizing and attaching to the 5' cap of mRNA
When the genome of a particular species is said to include 20,000 protein-coding regions, what does this imply?
there are also additional genes for RNAs other than mRNA
Where on a pre-mRNA transcript does a spliceosome bind?
to each end of an intron
In the 1920's, Hermann Muller discovered that X-rays caused genetic changes in Drosophila. In a related series of experiments in the 1940s, other scientists discovered that other types of chemicals have a similar effect. A new chemical food additive is developed by a cereal manufacturer. Why is it necessary to test for its ability to cause mutation?
we want to prevent any chance that it might cause mutation
