Chapter 17 Review Questions
In the process of transcription, _____.
RNA is synthesized
Which of the following statements best describes the promoter of a protein-coding gene?
The promoter is a nontranscribed region of a gene
Which of the following is not true of RNA processing? Nucleotides may be added at both ends of the RNA. A primary transcript is often much longer than the final RNA molecule that leaves the nucleus. Ribozymes may function in RNA splicing. Exons are cut out before mRNA leaves the nucleus. RNA splicing can be catalyzed by spliceosomes.
Exons are cut out before mRNA leaves the nucleus.
True or false. A tRNA with an anticodon complementary to the stop codon catalyzes the reaction by which translation is terminated.
False
True or false? A codon is a group of three bases that can specify more than one amino acid.
False
What is the process called that converts the genetic information stored in DNA to an RNA copy?
Transcription
The process, performed by the ribosome, of reading mRNA and synthesizing a protein is called...
Translation
What are the stop codons?
UAG, UGA, UAA Nearly every protein-coding sequence ends with one of the three stop codons (UAA, UAG, and UGA), which do not code for amino acids but signal the end of translation.
Suppose that a portion of double-stranded DNA in the middle of a large gene is being transcribed by an RNA polymerase. As the polymerase moves through the sequence of six bases shown in the diagram below, what is the corresponding sequence of bases in the RNA that is produced?
UGAGCC There are three principles to keep in mind when predicting the sequence of the mRNA produced by transcription of a particular DNA sequence. The RNA polymerase reads the sequence of DNA bases from only one of the two strands of DNA: the template strand. The RNA polymerase reads the code from the template strand in the 3' to 5' direction and thus produces the mRNA strand in the 5' to 3' direction. In RNA, the base uracil (U) replaces the DNA base thymine (T). Thus the base-pairing rules in transcription are A→U, T→A, C→G, and G→C, where the first base is the coding base in the template strand of the DNA and the second base is the base that is added to the growing mRNA strand.
The anticodon of a particular tRNA molecule is
complementary to the corresponding mRNA codon.
What name is given to the process in which the information encoded in a strand of mRNA is used to construct a protein?
translation
tRNA Properties
has amino acids covalently attached, contains an anticodon
After an RNA molecule is transcribed from a eukaryotic gene, what are removed and what are spliced together to produce an mRNA molecule with a continuous coding sequence?
introns ... exons
In eukaryotic cells, transcription cannot begin until
several transcription factors have bound to the promoter.
Translation requires _____.
mRNA, tRNA, and rRNA
Place the events in the transcription of a gene in their proper order from left (first event) to right (last event). Rank from first event to last event.
1) RNA polymerase binds promoter 2) RNA polymerase transcribes gene 3) RNA polymerase reaches terminator 4) RNA polymerase exit gene. RNA is released
Put the following events of elongation in prokaryotic translation in chronological order. 1. Binding of mRNA with small ribosomal subunit 2. Recognition of initiation codon 3. Complementary base pairing between initiator codon and anticodon of initiator tRNA 4. Base pairing of the mRNA codon following the initiator codon with its complementary tRNA 5. Attachment of the large subunit 2, 1, 4, 3, 5 5, 4, 3, 2, 1 1, 2, 3, 5, 4 1, 2, 3, 4, 5
1, 2, 3, 5, 4
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'
The direction of synthesis of an RNA transcript is _____.
5' —> 3'
Using Figure 17.5 in your textbook, identify a 5' → 3' sequence of nucleotides in the DNA template strand for an mRNA coding for the polypeptide sequence Phe-Pro-Lys.
5'-AAAACCTTT-3
Which of these is currently considered the best definition of a gene?
A gene codes for either a polypeptide or an RNA molecule
Which of the following statements about mutations is false? A deletion mutation results in the loss of a base in the DNA sequence. Addition and deletion mutations disrupt the primary structure of proteins. An addition mutation results in an added base in the DNA sequence. A knock-out mutation results in a total absence of the mutated protein.
A knock-out mutation results in a total absence of the mutated protein.
During elongation, which site in the ribosome represents the location where a codon is being read?
A site
Transcription begins at a promoter. What is a promoter?
A site in DNA that recruits the RNA Polymerase
After transcription begins, several steps must be completed before the fully processed mRNA is ready to be used as a template for protein synthesis on the ribosomes. Which three statements correctly describe the processing that takes place before a mature mRNA exits the nucleus? Which three statements correctly describe the processing that takes place before a mature mRNA exits the nucleus? A) A cap consisting of a modified guanine nucleotide is added to the 5' end of the pre-mRNA. B) A translation stop codon is added at the 3' end of the pre-mRNA. C) Noncoding sequences called introns are spliced out by molecular complexes called spliceosomes. D) Coding sequences called exons are spliced out by ribosomes. E) A poly-A tail (50-250 adenine nucleotides) is added to the 3' end of the pre-mRNA.
A) A cap consisting of a modified guanine nucleotide is added to the 5' end of the pre-mRNA. C) Noncoding sequences called introns are spliced out by molecular complexes called spliceosomes. E) A poly-A tail (50-250 adenine nucleotides) is added to the 3' end of the pre-mRNA.
At which site do new aminoacyl tRNAs enter the ribosome during elongation?
A-site
A particular triplet of bases in the coding strand of DNA is AAA. The anticodon on the tRNA that binds this mRNA codon is _____.
AAA
What is a start codon?
AUG Nearly every mRNA gene that codes for a protein begins with the start codon, AUG, and thus begins with a methionine.
Which of the following molecules is/are produced by translation? Include molecules that are subject to further modification after initial synthesis. Select all that apply. RNA polymerase Aminoacyl-tRNA synthetase The amino acid glycine
Aminoacyl-tRNA synthetase RNA polymerase
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?
An addition mutation and a deletion mutation.
What determines which base is to be added to an RNA strand during transcription?
Base pairing between the DNA template strand and the RNA nucleotides
The tRNA anticodon, GAC, is complementary to the mRNA codon with the sequence _____
CUG
Which of the following terms best describes the relationship between the newly synthesized RNA molecule and the DNA template strand?
Complementary
mRNA Properties
Contains exons, Specifies the amino acid sequence for a protein
Attachment of an amino acid to tRNA occurs in the
Cytoplasm
Life as we know it depends on the genetic code: a set of codons, each made up of three bases in a DNA sequence and corresponding mRNA sequence, that specifies which of the 20 amino acids will be added to the protein during translation. Imagine that a prokaryote-like organism has been discovered in the polar ice on Mars. Interestingly, these Martian organisms use the same DNA → RNA → protein system as life on Earth, except that there are only 2 bases (A and T) in the Martian DNA, and there are only 17 amino acids found in Martian proteins. Based on this information, what is the minimum size of a codon for these hypothetical Martian life-forms? A. 2 bases B. 3 bases C. 4 bases D. 5 bases E. 6 bases F. The answer cannot be determined from the information provided.
D. 5 bases In the most general case of x bases and y bases per codon, the total number of possible codons is equal to xy . In the case of the hypothetical Martian life-forms, is the minimum codon length needed to specify 17 amino acids is 5 (25 = 32), with some redundancy (meaning that more than one codon could code for the same amino acid). For life on Earth, x = 4 and y = 3; thus the number of codons is 43, or 64. Because there are only 20 amino acids, there is a lot of redundancy in the code (there are several codons for each amino acid).
In the diagram below, the two blue strands represent _____. The figure shows a blue molecule arranged in the form of a double chain. The gray unit on this figure represents an oval structure which contains unwound and unpaired chains of this molecule. Before and after this unit, the molecule is wound in the form of a double helix. A green unit represents a part of the double helix before the gray unit.
DNA
Which component is not directly involved in translation? tRNA mRNA ribosomes GTP DNA
DNA
Which of the following mutations would likely be most dangerous to a cell? Deletion of three nucleotides Substitution of one nucleotide for another Deletion of one nucleotide
Deletion of one nucleotide
If a DNA sequence is altered from TAGCTGA to TAGTGA, what kind of mutation has occurred?
Deletion.
Which of these correctly illustrates the pairing of DNA and RNA nucleotides?
GTTACG CAAUGC
Roles of RNA in protein synthesis in eukaryotes RNA plays important roles in many cellular processes, particularly those associated with protein synthesis: transcription, RNA processing, and translation. Drag the labels to the appropriate bins to identify the step in protein synthesis where each type of RNA first plays a role. If an RNA does not play a role in protein synthesis, drag it to the "not used in protein synthesis" bin.
In eukaryotes, pre-mRNA is produced by the direct transcription of the DNA sequence of a gene into a sequence of RNA nucleotides. Before this RNA transcript can be used as a template for protein synthesis, it is processed by modification of both the 5' and 3' ends. In addition, introns are removed from the pre-mRNA by a splicing process that is catalyzed by snRNAs (small nuclear RNAs) complexed with proteins. The product of RNA processing, mRNA (messenger RNA), exits the nucleus. Outside the nucleus, the mRNA serves as a template for protein synthesis on the ribosomes, which consist of catalytic rRNA (ribosomal RNA) molecules bound to ribosomal proteins. During translation, tRNA (transfer RNA) molecules match a sequence of three nucleotides in the mRNA to a specific amino acid, which is added to the growing polypeptide chain. RNA primers are not used in protein synthesis. RNA primers are only needed to initiate a new strand of DNA during DNA replication. SNRA/pre-mRNA/mRNA rRNA/tRNA RNA primers
Which of the following statements about ribozymes is/are correct? Select all that apply. Ribozymes are RNA molecules that function as enzymes. A ribosome can be regarded as one large ribozyme. In some genes, intron RNA functions as a ribozyme and catalyzes its own excision.
In some genes, intron RNA functions as a ribozyme and catalyzes its own excision. Ribozymes are RNA molecules that function as enzymes. A ribosome can be regarded as one large ribozyme.
_________________ of translation always happens at the start codon of the mRNA
Initiation
rRNA Properties
Is the most abundant form of RNA, is a component of ribosomes.
Which of the following is not true of a codon? It may code for the same amino acid as another codon. It is the basic unit of the genetic code. It consists of three nucleotides. It extends from one end of a tRNA molecule. It never codes for more than one amino acid
It extends from one end of a tRNA molecule.
What happens to RNA polymerase II after it has completed transcription of a gene?
It is free to bind to another promoter and begin transcription.
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.
Where does RNA polymerase begin transcribing a gene into mRNA?
It starts after a certain nucleotide sequence called a promoter
What is the function of RNA polymerase?
It unwinds the double helix and adds nucleotides to a growing strand of RNA.
What must occur before a newly made polypeptide is secreted from a cell?
Its signal sequence must target it to the ER, after which it goes to the Golgi.
Which of the following molecules are produced by transcription? Select all that apply. Ribozymes Ribosomal proteins Messenger RNA
Messenger RNA and Ribozymes
During translation, nucleotide base triplets (codons) in mRNA are read in sequence in the 5' → 3' direction along the mRNA. Amino acids are specified by the string of codons. What amino acid sequence does the following mRNA nucleotide sequence specify? 5′−AUGGCAAGAAAA−3′ Express the sequence of amino acids using the three-letter abbreviations, separated by hyphens (e.g., Met-Ser-Thr-Lys-Gly).
Met-Ala-Arg-Lys An amino acid sequence is determined by strings of three-letter codons on the mRNA, each of which codes for a specific amino acid or a stop signal. The mRNA is translated in a 5' → 3' direction.
The role of DNA in determining amino acid sequences Before a molecule of mRNA can be translated into a protein on the ribosome, the mRNA must first be transcribed from a sequence of DNA. The diagram shows a scheme of translation of DNA into a protein on the ribosome. There is a fragment of DNA with two strands (the strand from 3 prime to 5 prime is a template strand). The template strand is transcribed into mRNA (complementary nitrogenous bases are selected - U for A, A for T, C for G and G for C). Then the mRNA is translated into the protein of the ribosome, and each codon is translated into a certain amino acid (e. g., UGG is translated into Trp). The sequence of amino acids forms the protein. What amino acid sequence does the following DNA nucleotide sequence specify? 3′−TACAGAACGGTA−5′ Express the sequence of amino acids using the three-letter abbreviations, separated by hyphens (e.g., Met-Ser-His-Lys-Gly).
Met-Ser-Cys-His Before mRNA can be translated into an amino acid sequence, the mRNA must first be synthesized from DNA through transcription. Base pairing in mRNA synthesis follows slightly different rules than in DNA synthesis: uracil (U) replaces thymine (T) in pairing with adenine (A). The codons specified by the mRNA are then translated into a string of amino acids.
What does it mean when we say the genetic code is redundant?
More than one codon can specify the addition of the same amino acid.
The average length of a transcription unit along a eukaryotic DNA molecule is about 27,000 nucleotide pairs, whereas an averaged-sized protein is about 400 amino acids long. What is the best explanation for this fact? Many genes are subject to alternative RNA splicing. Each amino acid in a protein is encoded by a triplet of nucleotides. Most eukaryotic genes and their RNA transcripts have long noncoding stretches of nucleotides that are not translated.
Most eukaryotic genes and their RNA transcripts have long noncoding stretches of nucleotides that are not translated.
Which one of the following is true of tRNAs?
None of the above
Which mutation(s) would not change the remainder of the reading frame of a gene sequence that follows the mutation(s)? One addition and one deletion mutation. One addition and two deletion mutations. One deletion mutation. One addition mutation.
One addition and one deletion mutation.
DNA does not store the information to synthesize which of the following?
Organelles
The initiator tRNA attaches at the ribosome's _____ site.
P
Which of the following processes is an example of a post-translational modification?
Phosphorylation
The four levels of protein structure are primary, secondary, tertiary, and quaternary structure. Review the levels of protein structure by clicking the image below.
Primary structure--the unique amino acid sequence of a polypeptide Secondary structure--aspects of structure that result from hydrogen bonding between the backbone constituents of the polypeptide (Examples: α helix, β pleated sheet) Tertiary structure--the overall shape of a polypeptide, resulting from interactions between the side chains (R groups) of amino acids (Examples: hydrophobic interactions, van der Waals interactions, disulfide bridges, hydrogen bonds, and ionic bonds) Quaternary structure--the aggregation of multiple polypeptide subunits to form a functional protein
In the diagram below, the gray unit represents _____. The figure shows a blue molecule arranged in the form of a double chain. The gray unit on this figure represents an oval structure which contains unwound and unpaired chains of this molecule. Before and after this unit, the molecule is wound in the form of a double helix. A green unit represents a part of the double helix before the gray unit.
RNA polymerase
What name is given to the process in which pre-mRNA is edited into mRNA?
RNA processing
Where does translation take place?
Ribosome
Translation of cytoplasmic proteins occurs in the
Ribosomes
Which one of the following statements about RNA processing is true? RNA splicing can be catalyzed by tRNA. Ribozymes may function in RNA splicing. Exons are cut out before mRNA leaves the nucleus. A primary transcript is often much shorter than the final RNA molecule that leaves the nucleus
Ribozymes may function in RNA splicing.
Translation of secreted proteins occurs in the
Rough ER
___________ of translation happens when the ribosomes hits a stop codon on the mRNA
Termination
Which of the following steps occurs last in the initiation phase of translation?
The large ribosomal subunit joins the complex
What is meant by translocation?
The ribosome slides one codon down the mRNA.
How is translation initiated?
The small ribosomal subunit binds to the mRNA. The tRNA bearing methionine binds to the start codon. The large ribosomal subunit binds to the small one. The start codon signals the start of translation. All of the above.
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?
Two
Of the following, which is the most current description of a gene? a DNA subunit that codes for a single complete protein a DNA sequence that is expressed to form a functional product: either RNA or polypeptide a unit of heredity that causes formation of a phenotypic characteristic a discrete unit of hereditary information that consists of a sequence of amino acids
a DNA sequence that is expressed to form a functional product: either RNA or polypeptide
What is a ribozyme?
a biological catalyst consisting of DNA
What does a mutagen cause?
a change in the sequence of DNA
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 deletion of a codon a deletion of two nucleotides a substitution of the third nucleotide in an ACC codon a substitution of the first nucleotide of a GGG codon
a deletion of two nucleotides
Generally speaking, which of the following mutations would most severely affect the protein coded for by a gene? a base substitution at the beginning of the gene a base substitution at the end of the gene a frameshift deletion at the beginning of the gene a frameshift deletion at the end of the gene
a frameshift deletion at the beginning of the gene
During RNA processing a(n) _____ is added to the 3' end of the RNA.
a long string of adenine nucleotides A poly-A tail is added to the 3' end of the RNA.
Which of the following mutations would be most likely to have a harmful effect on an organism? a single nucleotide deletion near the end of the coding sequence a single nucleotide deletion in the middle of an intron a single nucleotide insertion downstream of, and close to, the start of the coding sequence a deletion of three nucleotides near the middle of a gene a nucleotide-pair substitution
a single nucleotide insertion downstream of, and close to, the start of the coding sequence
Amino acids are attached to tRNA by enzymes called...
aminoacyl-tRNA synthetase
What enzyme catalyzes the attachment of an amino acid to tRNA?
aminoacyl-tRNA synthetase
Polypeptides are assembled from _____
amino acids
Translation occurs in the _____.
cytoplasm Ribosomes, the sites of translation, are found in the cytoplasm.
The RNA segments joined to one another by spliceosomes are _____.
exons
The flow of information in a cell proceeds in what sequence?
from DNA to RNA to protein
Which of the following terms associated with transcription describe regions of nucleic acid?
gene, prometer, terminator
A nonsense mutation in a gene _____.
introduces a premature stop codon into the mRNA
According to the central dogma, what molecule should go in the blank? DNA → _____ → Proteins
mRNA
RNA processing converts the RNA transcript into _____.
mRNA
Which nucleic acid is translated to make a protein?
mRNA
During RNA processing a(n) _____ is added to the 5' end of the RNA.
modified guanine nucleotide The 5' cap consists of a modified guanine nucleotide.
Formation of ribosomal subunits occurs in the
nucleolus
Transcription of RNA processing occurs in the
nucleolus
Spliceosomes are composed of _____.
snRNPs and other proteins
The RNA that has an amino acid attached to it, and that binds to the codon on the mRNA, is called a ...
tRNA
During transcription in eukaryotes, a type of RNA polymerase called RNA polymerase II moves along the template strand of the DNA in the 3'→5' direction. However, for any given gene, either strand of the double-stranded DNA may function as the template strand. For any given gene, what ultimately determines which DNA strand serves as the template strand?
the base sequence of the gene's promoter In eukaryotes, binding of RNA polymerase II to DNA involves several other proteins known as transcription factors. Many of these transcription factors bind to the DNA in the promoter region (shown below in green), located at the 3' end of the sequence on the template strand. Although some transcription factors bind to both strands of the DNA, others bind specifically to only one of the strands. Transcription factors do not bind randomly to the DNA. Information about where each transcription factor binds originates in the base sequence to which each transcription factor binds. The positioning of the transcription factors in the promoter region determines how the RNA polymerase II binds to the DNA and in which direction transcription will occur.
In the diagram below, the green unit represents _____. The figure shows a blue molecule arranged in the form of a double chain. The gray unit on this figure represents an oval structure which contains unwound and unpaired chains of this molecule. Before and after this unit, the molecule is wound in the form of a double helix. A green unit represents a part of the double helix before the gray unit.
the promoter
A codon consists of _____ bases and specifies which _____ will be inserted into the polypeptide chain.
three ... amino acid
What name is given to the process in which a strand of DNA is used as a template for the manufacture of a strand of pre-mRNA?
transcription
