Key Concepts:
• Genes specify proteins via transcription and translation
• Transcription is the DNA-directed synthesis of RNA: A closer look
• Eukaryotic cells modify RNA after transcription
• Translation is the RNA-directed synthesis of a polypeptide: a closer look
• Mutation of one or a few nucleotides can affect protein structure and function
Terms : Hide Images
| 1814143280 | 5′ cap | a modified form of guanine nucleotide added onto the 5′ end of a pre-mRNA molecule | 0 | |
| 1814143281 | A Site | one of a ribosome's three binding sites for tRNA during translation; the A site holds the tRNA carrying the next amino acid to be added to the polypeptide chain. (A stands for aminoacyl tRNA.) | 1 | |
| 1814143282 | Alternative RNA Splicing | a type of eukaryotic gene regulation at the RNA-processing level in which different mRNA molecules are produced from the same primary transcript, depending on which RNA segments are treated as exons and which as introns | 2 | |
| 1814143283 | Aminoacyl-tRNA Synthetase | an enzyme that joins each amino acid to the appropriate tRNA | 3 | |
| 1814143284 | Anticodon | a nucleotide triplet at one end of a tRNA molecule that base-pairs with a particular complementary codon on an mRNA molecule | 4 | |
| 1814143285 | Codon | a three-nucleotide sequence of DNA or mRNA that specifies a particular amino acid or termination signal; the basic unit of the genetic code | 5 | |
| 1814143286 | Exon | a sequence within a primary transcript that remains in the RNA after RNA processing; also refers to the region of DNA from which this sequence was transcribed | 6 | |
| 1814143287 | Frameshift Mutation | a mutation occurring when nucleotides are inserted in or deleted from a gene and the number inserted or deleted is not a multiple of three, resulting in the improper grouping of the subsequent nucleotides into codons | 7 | |
| 1814143288 | Gene Expression | the process by which information encoded in DNA directs the synthesis of proteins or, in some cases, RNAs that are not translated into proteins and instead function as RNAs | 8 | |
| 1814143289 | Insertion | a mutation involving the addition of one or more nucleotide pairs to a gene | 9 | |
| 1814143290 | Intron | a noncoding, intervening sequence within a primary transcript that is removed from the transcript during RNA processing; also refers to the region of DNA from which this sequence was transcribed | 10 | |
| 1814143291 | Messenger RNA (mRNA) | a type of RNA, synthesized using a DNA template, that attaches to ribosomes in the cytoplasm and specifies the primary structure of a protein. (In eukaryotes, the primary RNA transcript must undergo RNA processing to become mRNA.) | 11 | |
| 1814143292 | Missense Mutation | a nucleotide-pair substitution that results in a codon that codes for a different amino acid | 12 | |
| 1814143293 | Mutagen | a chemical or physical agent that interacts with DNA and can cause a mutation | 13 | |
| 1814143294 | Mutation | a change in the nucleotide sequence of an organism's DNA or in the DNA or RNA of a virus | 14 | |
| 1814143295 | Nonsense Mutation | a mutation that changes an amino acid codon to one of the three stop codons, resulting in a shorter and usually nonfunctional protein | 15 | |
| 1814143296 | Nucleotide-Pair Substitution | a type of point mutation in which one nucleotide in a DNA strand and its partner in the complementary strand are replaced by another pair of nucleotides | 16 | |
| 1814143297 | P Site | one of a ribosome's three binding sites for tRNA during translation; the P site holds the tRNA carrying the growing polypeptide chain. (P stands for peptidyl tRNA.) | 17 | |
| 1814143298 | Point Mutation | a change in a single nucleotide pair of a gene | 18 | |
| 1814143299 | Poly-A Tail | a sequence of 50-250 adenine nucleotides added onto the 3′ end of a pre-mRNA molecule | 19 | |
| 1814143300 | Polyribosome (Polysome) | a group of several ribosomes attached to, and translating, the same messenger RNA molecule | 20 | |
| 1814143301 | Primary Transcript | an initial RNA transcript from any gene; also called pre-mRNA when transcribed from a protein-coding gene | 21 | |
| 1814143302 | Primase | an enzyme that joins RNA nucleotides to make a primer during DNA replication, using the parental DNA strand as a template | 22 | |
| 1814143303 | Promoter | a specific nucleotide sequence in the DNA of a gene that binds RNA polymerase, positioning it to start transcribing RNA at the appropriate place | 23 | |
| 1814143304 | Reading Frame | on an mRNA, the triplet grouping of ribonucleotides used by the translation machinery during polypeptide synthesis | 24 | |
| 1814143305 | Ribosomal RNA (rRNA) | RNA molecules that, together with proteins, make up ribosomes; the most abundant type of RNA | 25 | |
| 1814143306 | Ribosome | a complex of rRNA and protein molecules that functions as a site of protein synthesis in the cytoplasm; consists of a large and a small subunit. In eukaryotic cells, each subunit is assembled in the nucleolus; see also nucleolus | 26 | |
| 1814143307 | Ribozyme | an RNA molecule that functions as an enzyme, such as an intron that catalyzes its own removal during RNA splicing | 27 | |
| 1814143308 | RNA Polymerase | an enzyme that links ribonucleotides into a growing RNA chain during transcription, based on complementary binding to nucleotides on a DNA template strand | 28 | |
| 1814143309 | RNA Processing | modification of RNA primary transcripts, including splicing out of introns, joining together of exons, and alteration of the 5′ and 3′ ends | 29 | |
| 1814143310 | RNA Splicing | after synthesis of a eukaryotic primary RNA transcript, the removal of portions of the transcript (introns) that will not be included in the mRNA and the joining together of the remaining portions (exons) | 30 | |
| 1814143311 | Signal Peptide | a sequence of about 20 amino acids at or near the leading (amino) end of a polypeptide that targets it to the endoplasmic reticulum or other organelles in a eukaryotic cell | 31 | |
| 1814143312 | Signal-Recognition Particle (SRP) | a protein-RNA complex that recognizes a signal peptide as it emerges from a ribosome and helps direct the ribosome to the endoplasmic reticulum (ER) by binding to a receptor protein on the ER | 32 | |
| 1814143313 | Silent Mutation | a nucleotide-pair substitution that has no observable effect on the phenotype; for example, within a gene, a mutation that results in a codon that codes for the same amino acid | 33 | |
| 1814143314 | Spliceosome | a large complex made up of proteins and RNA molecules that splices RNA by interacting with the ends of an RNA intron, releasing the intron and joining the two adjacent exons | 34 | |
| 1814143315 | Start Point | in transcription, the nucleotide position on the promoter where RNA polymerase begins synthesis of RNA | 35 | |
| 1814143316 | TATA Box | a DNA sequence in eukaryotic promoters crucial in forming the transcription initiation complex | 36 | |
| 1814143317 | Template Strand | the DNA strand that provides the pattern, or template, for ordering, by complementary base pairing, the sequence of nucleotides in an RNA transcript | 37 | |
| 1814143318 | Terminator | in bacteria, a sequence of nucleotides in DNA that marks the end of a gene and signals RNA polymerase to release the newly made RNA molecule and detach from the DNA | 38 | |
| 1814143319 | Transcription | the synthesis of RNA using a DNA template | 39 | |
| 1814143320 | Transcription Factor | a regulatory protein that binds to DNA and affects transcription of specific genes | 40 | |
| 1814143321 | Transcription Initiation Complex | the completed assembly of transcription factors and RNA polymerase bound to a promoter | 41 | |
| 1814143322 | Transcription Unit | a region of DNA that is transcribed into an RNA molecule | 42 | |
| 1814143323 | Transfer RNA (tRNA) | an RNA molecule that functions as a translator between nucleic acid and protein languages by carrying specific amino acids to the ribosome, where they recognize the appropriate codons in the mRNA | 43 | |
| 1814143324 | Translation | the synthesis of a polypeptide using the genetic information encoded in an mRNA molecule; there is a change of "language" from nucleotides to amino acids | 44 | |
| 1814143325 | Triplet Code | a genetic information system in which sets of three-nucleotide-long words specify the amino acids for polypeptide chains | 45 | |
| 1814143326 | Wobble | flexibility in the base-pairing rules in which the nucleotide at the 5′ end of a tRNA anticodon can form hydrogen bonds with more than one kind of base in the third position (3′ end) of a codon | 46 | |
| 1869360603 | Who formulated the one gene-one enzyme hypothesis? a. Watson and Crick b. Beadle and Tatum c. Hershey and Chase d. Franklin e. None of the listed responses is correct. | Beadle and Tatum Restating Beadle and Tatum's idea as one gene-one polypeptide reflects the current idea that each polypeptide is specified by one gene. | 47 | |
| 1869360604 | Genetic information of eukaryotic cells is transferred from the nucleus to the cytoplasm in the form of __________. a. proteins b. lipids c. RNA d. carbohydrates e. DNA | RNA In transcription, a gene provides the instructions for synthesizing an mRNA molecule, a polynucleotide that enters the cytoplasm to be translated. | 48 | |
| 1869360605 | Which of the following statements is true? a. Each DNA base codes for three amino acids. b. Each gene codes for three proteins. c. It takes three genes to code for one protein. d. Each triplet has many different meanings. e. Each amino acid in a protein is coded for by three bases in the DNA. | Each amino acid in a protein is coded for by three bases in the DNA. The mRNA base triplets are called codons, each of which codes for the incorporation of a single amino acid. | 49 | |
| 1869360606 | When RNA is being made, the RNA base __________ always pairs with the base __________ in DNA. a. U ... T b. T ... G c. U ... A d. A ... U e. T ... A | U ... A In RNA, uracil takes the place of thymine and, like thymine, pairs with adenine. | 50 | |
| 1869360607 | Generally speaking, how many genetic codes are there? a. 20 b. one c. four d. one for each organism e. three | one Although slight variations do exist, the genetic code is essentially universal. Nearly all organisms use the same genetic code to translate mRNA to protein. | 51 | |
| 1869360608 | What mRNA codon would be made from the DNA triplet 3′-CGT-5′? a. 5′-ATU-3′ b. 5′-GCA-3′ c. 3′-TCU-5′ d. 5′-CTA-3′ e. 3′-GCA-5′ | 5′-GCA-3′ C pairs with G, and T pairs with A. | 52 | |
| 1869360609 | The number of nucleotide bases "read" together on the mRNA to designate each amino acid is __________; this unit is called a(n) __________. a. two ... dipeptide b. three ... triose c. two ... anticodon d. three ... codon e. one ... amino acid | three ... codon The mRNA base triplets are called codons. | 53 | |
| 1869360610 | The codons AAA, CCC, GGG, and UUU specify the amino acids lysine, proline, glycine, and phenylalanine, respectively. If the base sequence 5′-CCCAAATTTGGG-3′ is present in the coding strand of a stretch of DNA, what polypeptide sequence would be encoded by the corresponding template strand? a. lys-pro-gly-phe b. pro-lys-phe-gly c. gly-phe-lys-pro d. phe-gly-pro-lys e. gly-phe-pro-lys | pro-lys-phe-gly The sequence of the coding strand of the DNA is equivalent to that of the transcribed mRNA, except that it contains thymine where the mRNA has uracil. | 54 | |
| 1869360611 | How many nucleotides are needed to code for a protein with 450 amino acids? a. at least 150 b. at least 300 c. at least 450 d. at least 900 e. at least 1,350 | at least 1,350 Because the code is a triplet and three nucleotides code for the incorporation of one amino acid, 450 × 3, or at least 1,350, would be needed. | 55 | |
| 1869360612 | In many cases, more than one codon codes for the same amino acid. Because of this, we say that the code is __________. a. inaccurate b. incomplete c. not specific d. redundant e. tricky | redundant For example, there are six codons that code for the amino acid leucine. | 56 | |
| 1869360613 | Bacteria can transcribe and translate human genes to produce functional human proteins because __________. a. the genetic code is nearly universal b. bacterial ribosomes and eukaryotic ribosomes are identical c. eukaryotes do not really need a nucleus d. RNA has catalytic properties e. bacterial and eukaryotic RNA polymerases are identical | the genetic code is nearly universal All organisms use the same genetic code, so it is possible (and the basis of many biotech applications) to produce human proteins using another organism's protein synthesis machinery. | 57 | |
| 1869360614 | In a eukaryotic cell, transcription takes place __________. a. on the cell membrane b. in the rough endoplasmic reticulum c. in the cytoplasm d. on free ribosomes e. in the nucleus | in the nucleus In a eukaryotic cell, there is compartmentalization of function, with transcription occurring in the nucleus and translation occurring in the cytoplasm. | 58 | |
| 1869360615 | Which of the following best describes the arrangement of genetic information in a DNA molecule? a. A gene is composed of overlapping, three-nucleotide words on a template strand of DNA. b. The three-nucleotide words of a gene are serially arranged on both strands of DNA at a specific locus. c. The three-nucleotide words of a gene are arranged in a nonoverlapping series on the DNA template strand. d. Information in a gene is made up of two-, three-, or four-nucleotide words, depending on the amino acids specified. e. A gene is made up of a linear, nonoverlapping series of the amino acids in a polypeptide. | The three-nucleotide words of a gene are arranged in a nonoverlapping series on the DNA template strand. The series of nonoverlapping, three-nucleotide words of a gene are transcribed into a complementary series of nonoverlapping, three-nucleotide words in mRNA, which is then translated into a chain of amino acids. | 59 | |
| 1869360616 | Which of the following catalyzes the linkage between ribonucleotides to form RNA during gene expression? a. RNA polymerase b. aminoacyl-tRNA synthetase c. a ribozyme d. tyrosinase e. tRNA | RNA polymerase The enzyme responsible for transcription is RNA polymerase. | 60 | |
| 1869360617 | One strand of a DNA molecule has the following sequence: 3′-AGTACAAACTATCCACCGTC-5′. In order for that strand to be transcribed, there would have to be a specific recognition sequence, called a(n) __________, to the left of the DNA sequence indicated. a. centromere b. intron c. exon d. AUG codon e. promoter | promoter The region of DNA to which RNA polymerase attaches and initiates transcription is the promoter, which typically extends several dozen nucleotides "upstream" from the transcription start point. | 61 | |
| 1869360618 | During the transcription of a given portion of a DNA molecule __________. a. mRNA is synthesized on both chains of the DNA molecule at once b. mRNA is synthesized on both chains of the DNA molecule, but first on one side and then the other c. mRNA is synthesized on only one of the chains d. half of the mRNA is synthesized on half of one chain; then the other half of the mRNA is made on the other half of the DNA e. All of the listed responses are correct. | mRNA is synthesized on only one of the chains After binding to the promoter, the RNA polymerase initiates RNA synthesis at the start point on the template strand. Nucleotides from a pool within the cell are used to elongate the growing strand of RNA. Nucleotide sequences within the promoter determine in which direction the polymerase faces and which strand is used as the template. | 62 | |
| 1869360619 | In transcription, __________. a. the promoter region acts as an initial binding site for RNA polymerase b. only one of the DNA strands is used as the template c. the RNA nucleotides used are produced by the cell d. All of the listed responses are correct. e. None of the listed responses is correct. | All of the listed responses are correct. After binding to the promoter, the RNA polymerase initiates RNA synthesis at the start point on the template strand. Nucleotides from a pool within the cell are used to elongate the growing strand of RNA. Nucleotide sequences within the promoter determine in which direction the polymerase faces and which strand is used as the template. | 63 | |
| 1869360620 | Which of the following statements is FALSE? a. In bacteria, proteins called transcription factors enhance the affinity of RNA polymerase to the promoter sites of genes. b. In bacteria, transcription of a gene is initiated when the RNA polymerase by itself recognizes and binds to the promoter of the gene. c. The initiation of gene transcription in eukaryotes requires the binding of proteins called transcription factors to the TATA box in the promoter region of a gene. d. In eukaryotes, transcription factors generally bind to a specific DNA region containing the sequence TATA before RNA polymerase can bind to the promoter. e. All of the listed responses are correct. | In bacteria, proteins called transcription factors enhance the affinity of RNA polymerase to the promoter sites of genes. This statement is false. Transcription factors are required to initiate transcription in eukaryotes. In bacteria, the RNA polymerase alone can bind to the promoter site of a gene. | 64 | |
| 1869360621 | In eukaryotes, which of the following mechanisms operates after transcription, but before translation of mRNA into protein? a. RNA splicing b. DNA packaging into nucleosomes c. action of repressors and activators d. construction of a transcription initiation complex e. All of the listed responses are correct. | RNA splicing Introns are deleted and exons are spliced together after transcription and before translation. | 65 | |
| 1869360622 | Which of the following accurately describes the usual process of transcription for eukaryotic genes? a. Exons are not transcribed. b. Introns are not transcribed. c. Both introns and exons are transcribed, but the RNA transcribed from introns does not leave the nucleus. d. Both introns and exons are transcribed, but neither type of transcribed region leaves the nucleus. e. Exons and introns are transcribed, and the RNA transcribed from both types of transcribed region leaves the nucleus. | Both introns and exons are transcribed, but the RNA transcribed from introns does not leave the nucleus. The noncoding elements that lie between coding regions, called introns, are spliced out of the mRNA during processing. The pre-mRNA never leaves the nucleus; only the processed message enters the cytoplasm for translation. | 66 | |
| 1869360623 | Which of the following statements correctly describes mRNA processing? a. Introns are cut out of the primary transcript, and the resulting exons are spliced together. b. Exons are cut out of the primary transcript, and the introns are spliced together. c. Introns are cut out of the primary transcript and spliced together at the end of the transcript. d. Exons are cut out of the primary transcript and transported to the endoplasmic reticulum. e. Introns are cut out of the primary transcript and transported to the ribosomes. | Introns are cut out of the primary transcript, and the resulting exons are spliced together. Introns are removed and exons spliced together before the mRNA enters the cytoplasm for translation. | 67 | |
| 1869360624 | A cell biologist found that two different proteins with largely different structures were translated from two different mRNAs. These mRNAs, however, were transcribed from the same template within the cell nucleus. Which mechanism below could best account for this? a. Different systems of DNA unpacking could result in two different mRNAs. b. A point mutation might have altered the gene. c. Exons from the same gene could be spliced in different ways to make different mRNAs. d. Different transcription factors were involved in the transcription of the two mRNAs. e. The two proteins have different functions in the cell. | Exons from the same gene could be spliced in different ways to make different mRNAs. In fruit flies, for example, sex differences are primarily the result of differences in RNA splicing. | 68 | |
| 1869360625 | What is a key difference in gene expression between eukaryotic and prokaryotic cells? a. In prokaryotes, proteins are assembled directly from DNA. b. RNA polymerases are involved only in initiation of transcription in eukaryotes. c. In prokaryotic cells, the RNA transcript is immediately available as mRNA without processing. d. In eukaryotic cells, transcribed RNA sequences function as termination signals. e. Prokaryotes do not contain ribosomes. | In prokaryotic cells, the RNA transcript is immediately available as mRNA without processing. Because it lacks a nucleus, a prokaryote can simultaneously transcribe and translate the same gene. | 69 | |
| 1869360626 | At one point, as a cell carried out its day-to-day activities, the nucleotides GAT were paired with the nucleotides CUA. This pairing occurred __________. a. in a double-stranded DNA molecule b. during translation c. during transcription d. when an mRNA codon paired with a tRNA anticodon e. It is impossible to say, given this information. | during transcription The CUA of an RNA strand is complementary to the GAT of a DNA strand. | 70 | |
| 1869360627 | The function of tRNA during protein synthesis is to __________. a. deliver amino acids to their proper site during protein synthesis b. guide ribosomal subunits out of the nucleus through nuclear pores c. attach mRNA to the small subunit of the ribosome d. process mRNA e. transcribe mRNA | deliver amino acids to their proper site during protein synthesis Each tRNA molecule is used repeatedly, picking up its designated amino acid in the cytosol, depositing this cargo at the ribosome, and leaving the ribosome to pick up another load. | 71 | |
| 1869360628 | Which of the following summaries of protein synthesis is correct? a. Replicated DNA leaves the nucleus, is transported to a ribosome, and catalyzes the polymerization of amino acids in a protein. b. DNA exchanges its thymine units with uracil in polymerase. This activates polymerase, and it starts joining amino acids together. c. Transfer RNAs line up on a ribosome, and amino acids bind to them with hydrogen bonds. d. Messenger RNA is made on a DNA template, and then amino-acid-bearing transfer RNAs bind to the mRNA through codon-anticodon pairing. e. DNA strands separate in the nucleus to form mRNA. mRNA leaves the nucleus and is transcribed into tRNA on ribosomes. | Messenger RNA is made on a DNA template, and then amino-acid-bearing transfer RNAs bind to the mRNA through codon-anticodon pairing. Genes program protein synthesis via genetic messages in the form of mRNA. The mRNA is read to produce a polypeptide on a ribosome, where tRNA molecules bring amino acids for incorporation into the growing polypeptide. | 72 | |
| 1869360629 | The bonds that hold tRNA molecules in the correct three-dimensional shape are __________. a. peptide linkages b. hydrophobic interactions c. covalent bonds d. ionic bonds e. hydrogen bonds | hydrogen bonds Nucleotide bases in certain regions of the tRNA strand form hydrogen bonds with complementary bases from other regions. | 73 | |
| 1869360630 | During translation in a eukaryotic cell, __________. a. ribosomes move into the nucleus b. tRNA carries amino acid molecules to the nucleus, where they are added to a growing polypeptide chain c. polypeptides are synthesized at ribosomes, according to instructions carried by mRNA d. mRNA is synthesized by the bonding of free nucleotides to the bases on the template strand of DNA e. ribosomes move out of the nucleus | polypeptides are synthesized at ribosomes, according to instructions carried by mRNA Amino acids are brought to the ribosome by tRNA and added to the end of a growing polypeptide chain. | 74 | |
| 1869360631 | The P site of a ribosome does which of the following? a. It holds the tRNA that is carrying the next amino acid to be added to the growing polypeptide chain. b. It holds the tRNA carrying the growing polypeptide chain. c. It helps "unzip" DNA during transcription. d. It catalyzes the addition of amino acids to the tRNAs. e. It recognizes the promoter during transcription initiation. | It holds the tRNA carrying the growing polypeptide chain. The P site (peptidyl-tRNA site) holds the tRNA carrying the growing polypeptide chain, whereas the A site (aminoacyl-tRNA site) holds the tRNA carrying the next amino acid to be added to the chain. | 75 | |
| 1869360632 | The first amino acid inserted into a new polypeptide chain in eukaryotic cells is usually __________. a. glycine b. serine c. methionine d. adenosine monophosphate e. alanine | methionine The initiator tRNA, which carries the amino acid methionine, attaches to the initiation codon. | 76 | |
| 1869360633 | Which of the following is a post-translational modification of a polypeptide? a. cleavage of a polypeptide into two or more chains b. removal of introns and splicing of exons c. formation of a polysome that allows simultaneous formation of many polypeptides from one mRNA transcript d. The growing polypeptide signals the ribosome to attach to the ER. e. complementary base pairing of mRNA and tRNA in the ribosome | cleavage of a polypeptide into two or more chains Once a polypeptide has been formed during translation, it can undergo post-translational modifications. | 77 | |
| 1869360634 | During translation, amino acid chain elongation occurs until __________. a. no further amino acids are needed by the cell b. all tRNAs are empty c. the polypeptide is long enough d. the ribosome encounters a "stop" codon e. the ribosome runs off the end of the mRNA strand | the ribosome encounters a "stop" codon Elongation continues until a stop codon occupies the A site of the ribosome. | 78 | |
| 1869360635 | Polysomes may be defined as __________. a. microfilaments and microtubules b. groups of lysosomes degrading the same protein c. groups of ribosomes translating the same mRNA d. groups of chromosomes e. groups of peroxisomes | groups of ribosomes translating the same mRNA Polysomes are strings of ribosomes reading the same mRNA. | 79 | |
| 1869360636 | Cells are able to distinguish proteins destined for secretion or for segregation to specific intracellular compartments from those that will remain in the cytoplasm because __________. a. there are two types of ribosomes: one group that synthesizes cytoplasmic proteins only, and another type that synthesizes secreted or compartment-specific proteins only b. some proteins, as they begin to be synthesized, contain a signal region that causes the ribosome with its growing polypeptide to attach to the ER and translocate the polypeptide into the lumen (space) of the ER c. proteins destined for secretion or for a specific compartment are all synthesized in the nucleus, whereas cytoplasmic proteins are all synthesized in the cytoplasm d. each compartment in the cell (the nucleus, lysosome, and so forth) has its own set of ribosomes that synthesize proteins unique to that compartment e. ribosomes contain two types of subunits | some proteins, as they begin to be synthesized, contain a signal region that causes the ribosome with its growing polypeptide to attach to the ER and translocate the polypeptide into the lumen (space) of the ER The synthesis of all proteins begins in the cytosol. Only if the polypeptides are destined for the endomembrane system or for secretion will they contain a signal peptide, which targets the protein to the endoplasmic reticulum. | 80 | |
| 1869360637 | Consider the following list of events in the expression of a eukaryotic gene. What is their proper sequence? 1. translation 2. RNA processing 3. transcription 4. modification of protein a. 1, 2, 3, 4 b. 3, 2, 1, 4 c. 4, 2, 3, 1 d. 2, 3, 4, 1 e. 1, 2, 4, 3 | 3, 2, 1, 4 In eukaryotic cells, the transcription of a pre-mRNA is followed by processing. The mRNA then moves to the cytoplasm, where ribosomes construct a polypeptide based on the codons in the RNA. The polypeptide is then modified, if necessary. | 81 | |
| 1869360638 | The mRNA codons 5′-CAA-3′ or 5′-CAG-3′ are translated as the amino acid glutamine by __________. a. the tRNA with an anticodon 5′-GUU-3′ and glutamine at its other end b. by tRNA molecules that have been charged with glutamine by two different aminoacyl-tRNA synthetases c. separate tRNA molecules with anticodons 3′-GUU-5′ and 3′-GUC-5′, respectively d. the same tRNA with the anticodon 3′-GUU-5′ e. the small and large ribosomal units | the same tRNA with the anticodon 3′-GUU-5′ Because a tRNA anticodon with U at its 5′ end can pair with either A or G in the third position (at the 3′ end) of an mRNA codon, the same tRNA can correctly translate both of these codons as glutamine. | 82 | |
| 1869360639 | Which of the following statements regarding the structure and function of tRNA is FALSE? a. Each type of tRNA molecule translates a particular mRNA codon into a particular amino acid. b. Although each tRNA consists of a relatively short, single RNA strand, this single strand can achieve a three-dimensional structure by folding back upon itself and forming covalent bonds between complementary bases. c. The nucleotide sequence at both the amino acid attachment and the anticodon ends of each tRNA is instrumental in specifying which amino acid is attached to the tRNA by aminoacyl-tRNA synthetase. d. Although there are 61 codons that code for amino acids, there are only 45 different tRNA molecules. e. The second and third listed responses are false. | Although each tRNA consists of a relatively short, single RNA strand, this single strand can achieve a three-dimensional structure by folding back upon itself and forming covalent bonds between complementary bases. This statement is false. Complementary stretches of nucleotides pair by hydrogen bonds, allowing the single strand of RNA to take on a three-dimensional structure. | 83 | |
| 1869360640 | A geneticist found that a particular mutation had no effect on the polypeptide encoded by the gene. This mutation probably involved __________. a. the deletion of one nucleotide b. a missense mutation c. the insertion of one nucleotide d. a nonsense mutation e. a silent or neutral mutation | a silent or neutral mutation Silent mutations are attributable to the redundancy of the genetic code. | 84 | |
| 1869360641 | Which of the following types of mutation is LEAST likely to affect the function of the protein corresponding to the gene in which the mutation occurs? a. addition of single bases b. base-pair substitution c. insertion of three bases d. deletion of single bases e. nonsense mutation | base-pair substitution Base substitutions can be silent (having no effect on the encoded protein), minor (changing the amino acid to one with similar properties or being located in an unimportant portion of the protein), or major (changing an amino acid that has significant effects on the activity of the protein). Insertions and deletions usually have disastrous effects. | 85 | |
| 1869360642 | A base-pair substitution mutation in a germ cell line is likely to have NO effect on phenotype if the substitution __________. a. forms a new stop codon b. occurs in an intron c. changes a stop codon to a codon specifying an amino acid d. changes the structure of an enzyme e. prevents the initiation of transcription of the DNA sequence that codes for ATP synthase | occurs in an intron A base substitution in an intron that does not change the amino acid sequence of the polypeptide encoded by that gene would have no phenotypic effect on the organism. | 86 | |
| 1869360643 | A virus infects a cell and randomly inserts many short segments of DNA containing a stop codon throughout an organism's chromosomes. This will probably cause __________. a. manufactured proteins to be short and defective b. the DNA to break up into thousands of short segments c. incorrect pairing between mRNA codons and amino acids d. no bad effects, as long as the stop codons are not also inserted into tRNA e. All of the listed responses are correct. | manufactured proteins to be short and defective Alterations that insert stop codons cause premature termination of the polypeptides. | 87 | |
| 1869360644 | A point mutation in which a single base pair is inserted or deleted from DNA is called a(n) __________. a. nonsense mutation b. frame-shift mutation c. inversion mutation d. silent mutation e. missense mutation | frame-shift mutation Insertions or deletions alter the reading frame (triplet grouping) of the genetic message. Such mutations are called frame-shift mutations. | 88 | |
| 1869360645 | Ultraviolet (UV) radiation is damaging to cells because it __________. a. pokes holes in the nuclear envelope b. blocks all translation c. causes mutations in the DNA d. deactivates the enzymes needed for DNA replication e. leads to disassembly of the cytoskeleton | causes mutations in the DNA Mutagenic radiation is an example of a physical mutagen; this includes UV light, which can produce disruptive thymine dimers in DNA. | 89 | |
| 1869360646 | When genes are expressed, they produce __________. a. enzymes b. RNA molecules c. phenotypic traits d. polypeptides e. The second and fourth responses are correct. | The second and fourth responses are correct. It now appears that DNA codes for both polypeptides and many types of functional RNA molecules. | 90 | |
| 1869365616 | In eukaryotic cells, transcription cannot begin until a. DNA nucleases have isolated the transcription unit. b. the 59 caps are removed from the mRNA. c. several transcription factors have bound to the promoter. d. the two DNA strands have completely separated and exposed the promoter. e. the DNA introns are removed from the template. | several transcription factors have bound to the promoter. | 91 | |
| 1869365617 | Which of the following is not true of a codon? a. It extends from one end of a tRNA molecule. b. It consists of three nucleotides. c. It may code for the same amino acid as another codon. d. It never codes for more than one amino acid. e. It is the basic unit of the genetic code. | It extends from one end of a tRNA molecule. | 92 | |
| 1869365618 | The anticodon of a particular tRNA molecule is a. complementary to the corresponding triplet in rRNA. b. complementary to the corresponding mRNA codon. c. the part of tRNA that bonds to a specific amino acid. d. changeable, depending on the amino acid that attaches to the tRNA. e. catalytic, making the tRNA a ribozyme. | complementary to the corresponding mRNA codon. | 93 | |
| 1869365619 | Which of the following is not true of RNA processing? a. Exons are cut out before mRNA leaves the nucleus. b. Ribozymes may function in RNA splicing. c. RNA splicing can be catalyzed by spliceosomes. d. A primary transcript is often much longer than the final RNA molecule that leaves the nucleus. e. Nucleotides may be added at both ends of the RNA. | Exons are cut out before mRNA leaves the nucleus. | 94 | |
| 1869365620 | Which component is not directly involved in translation? a. GTP b. ribosomes c. Mrna d. DNA e. tRNA | DNA | 95 | |
| 1869365621 | Using Figure 17.5, identify a 59 S39 sequence of nucleotides in the DNA template strand for an mRNA coding for the polypeptide sequence Phe-Pro-Lys. a. 5'-AAACCCUUU-3' b. 5'-CTTCGGGAA-3' c. 5'-AAAACCTTT-3' d. 5'-GAACCCCTT-3' e. 5'-UUUGGGAAA-3' | 5'-CTTCGGGAA-3' | 96 | |
| 1869365622 | Which of the following mutations would be most likely to have a harmful effect on an organism? a. a single nucleotide deletion near the end of the coding sequence b. a single nucleotide deletion in the middle of an intron c. a nucleotide-pair substitution d. a single nucleotide insertion downstream of, and close to, the start of the coding sequence e. a deletion of three nucleotides near the middle of a gene | a single nucleotide insertion downstream of, and close to, the start of the coding sequence | 97 |
