Chapter 10: Gene Expression

25 July 2022
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RNA polymerase uses the _______ DNA template to synthesize a _______ mRNA
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3β€²-to-5β€²; 5β€²-to-3β€²
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During initiation, the sequence of DNA to which RNA polymerase binds most tightly is the..
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Promoter
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What is true about the genetic code?
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Eukaryotes, archaea, and bacteria each evolved the genetic code independently The common ancestor of eukaryotes and archaea evolved the genetic code independently from the one evolved by bacteria The common ancestor of eukaryotes and bacteria evolved the genetic code independently from the one evolved by archaea
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In eukaryotes, a promoter is the region of what?
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DNA that binds RNA polymerase
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The anticodon 3β€²-AUC-5β€² would pair with what codon?
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5β€²-UAG-3β€².
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What is true about promoters?
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Some promoters are more efficient than others at initiating transcription Bacterial genes do not lack promoters Promoters provide information that orients RNA polymerase to the strand of the DNA it should use as a template A promoter is a DNA sequence.
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Which of the following molecules is most involved in the transfer of genetic information from the nucleus to the cytoplasm?
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mRNA
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Suppose that the coding region of a gene contains 1,800 base pairs, with 570 in exon 1, 420 in exon 2, and 810 in exon 3. The length of the protein translated from this gene is _______ amino acids.
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600
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Synthesis of ribosomal RNA (rRNA) occurs..
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in the 5' to 3' direction
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What is required for transcription?
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A DNA template RNA polymerase Appropriate nucleoside triphosphates
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RNA polymerase is a..
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Protein
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A polysome is what?
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The structure formed when multiple ribosomes are translating an mRNA molecule
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Termination of transcription involves what?
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A terminator sequence
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Suppose that a certain mRNA is transcribed at a normal rate in the nucleus, but it is found at very low levels in the cytoplasm. Which of the following would be the most plausible explanation for this phenomenon?
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A defect in the addition of the poly A tail on the pre-mRNA
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At which of the following sites on the ribosome is the tRNA never charged?
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E
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Proteins are synthesized starting at the _______ of the polypeptide, in the _______ direction along the mRNA
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N terminus; 5β€²-to-3β€²
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After translation, the polypeptide chains of some proteins are cut by a process called what?
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Proteolysis
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Actin, a protein found in almost all eukaryotic cells, is expressed in most cell types at a fairly constant level. Thus, the gene that codes for actin can be considered a(n) _______ gene
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Constitutive
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What are potential points of regulation in gene expression?
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Transcription factor Inducible Repressible Enhanced
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In the process of protein synthesis, which of the following must take place in order to ensure that the protein made is the one specified by mRNA?
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The tRNAs must read the mRNA correctly and the tRNAs must deliver the correct amino acids for the mRNA codons
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If a 5β€²-to-3β€² strand of DNA has the sequence GTCTATGCATTA, what would be the sequence of the resulting transcribed RNA?
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5β€²-GUCUAUGCAUUA-3β€²
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A transcription factor is a _______ that binds to _______.
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Protein; DNA
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The process by which information in the nucleic acid sequence is used to direct the production of a specific chain of amino acids is called what?
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Translation
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Put the following four steps of eukaryotic gene expression in order, from beginning to end. (1) Pre-mRNA is processed to make mRNA. (2) Ribosomes translate the mRNA message to make proteins. (3) mRNA is transported to the cytoplasm. (4) DNA is used as a template make pre-mRNA.
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4; 1; 3; 2
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Posttranslational alterations of proteins..
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Can affect the activity of an enzyme May include addition of phosphate groups May include the addition of polysaccharides to proteins May include the cleavage of signal sequences
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What is involved in the elongation step of translation?
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Peptidyl transferase Ribosomes Charged tRNA The amino acid site
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RNA polymerases differ from DNA polymerases how?
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RNA polymerases are less effective at proofreading than DNA polymerases
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Sickle-cell disease and hemoglobin C disease are both caused by point mutations, resulting in glutamic acid being replaced by _______ and _______, respectively
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Valine; lysine
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During protein synthesis, ribosomes..
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Translate mRNA into polypeptides
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At the initiation of translation in eukaryotes..
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The anticodon of tRNA charged with methionine binds to mRNA associated with the small ribosomal subunit
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In eukaryotes, the first amino acid in a growing polypeptide chain is always _______ because the only codon for this amino acid is also the _______ codon
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Methionine; start
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Which component of transcribed RNA in eukaryotes is present in the primary transcript but is removed before translation occurs?
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Intron
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The mRNA codon for leucine is 5Β΄-UUG-3Β΄, and the tRNA anticodon is..
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3β€²-AAC-5β€².
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Why did the original "one-gene, one-enzyme" hypothesis have to be modified?
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Some enzymes are made up of more than one polypeptide
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What is true about tRNA?
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Can bind a specific amino acid and recognize a specific sequence of nucleotides in mRNA by complementary base pairing Specific enzymes bind amino acids to their corresponding tRNAs tRNAs interact with mRNA ATP is required for the charging of tRNAs with amino acids tRNAs interact with ribsomes
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What is true about pre-mRNA splicing?
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It removes introns It shortens the RNA molecule It's not common in prokaryotes It is directed by consensus sequences It is performed by small nuclear ribonucleoprotein particles (snRNPs)
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Predict the intracellular destinations of the following proteins: DNA polymerase; pyruvate kinase; rubisco; citrate synthase
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Nucleus; cytoplasm; chloroplast; mitochondrion
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Ribosomes..
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Carry out translation
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What is an example of single-base substitutions in the template strand of DNA that would result in the premature termination of translation?
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ATG to ATT
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UAU and UAC both code for tyrosine. A change from UAU to UAC would thus be a(n) _______ mutation; a change from UAU to UAG would be a(n) _______ mutation
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Silent; nonsense
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In the elongation stage of translation..
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rRNA is catalytically active
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A protein destined for a lysosome carries a signal peptide for what?
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Rough ER
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What is required for the initiation of transcription?
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Promoter DNA
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A mutation that is inherited has to be what?
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A germ line cell (sperm and eggs)
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What are the three consequences of mutations?
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Accumulation can kill cells Mutations in germ cell DNA can affect viability of offspring DNA damage can cause cancer
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What is a covalent linkage between adjacent thymine bases. Occurs when DNA is damaged by UV light. That DNA does not get copied properly and a mutation is introduced?
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A thymine dimer
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What is ligation?
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Occurs during DNA repair where DNA ligase seals the DNA strand up
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What is the protein coding sequence?
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Going from the start to the stop codon
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What are proteins that control what genes are transcribed?
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Transcription factors (TF)
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What binds to the promoter?
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TF
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What are the steps of transcription?
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1. RNA polymerase performs transcription (enzyme complex) 2.TF binds to the promoter 3.RNA polymerase separates the two DNA strands starting at the promoter 4.A complementary strand is constructed by reading what's on the DNA and pairing it with the complementary base; RNA is a single stranded molecule so you only need one template 5.RNA polymerase comes to the transcription stop sequence 6.RNA polymerase stops transcribing, moves away from it, last of the gene is closed back up
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True or False? The RNA promoter is transcribed
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False
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What are the stop codons?
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UAA/UAG/UGA
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When is the only time nucleic acids are read from the 5'-to-3' direction?
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During translation
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The gene sequence is the ______ of the complementary of the template strand.
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Reverse
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What carries amino acids to the ribosome during translation?
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tRNA
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What are the three active enzyme sites in a ribosome?
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E (exit), P (enzyme/peptide site; where peptide bonds are formed), A (amino acid site, where incoming transfer RNA with their amino acid enters the ribosome)
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What are the three parts of translation?
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Initiation, elongation, and termination
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What occurs during initiation?
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1.mRNA binds to the small ribosomal subunit such that the start codon is in the P site 2.1st tRNA (anticodon UAC) carrying Methionine binds to the start codon in the P-site of the small ribosomal subunit 3.Large ribosomal subunit binds to the small ribosomal subunit, the mRNA and the tRNA (small ribosomal subunit, mRNA and tRNA already assimilated) P and A sites complete
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What occurs during elongation?
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1.2nd tRNA carrying its amino acid binds to the A site of the ribosome (codon to anticodon pairing 2.Bond forms between the two amino acids (forms in the P site) 3.Translocation when the tRNA and RNA move from the A to the P site 4.A: tRNA in the E site leaves the ribosome B: Another tRNA with its amino acid moves into the A site (codon-anticodon pairing) 5.Peptide bond forms β†’ elongation of peptide chain 6.Repeat
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What occurs during termination?
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1.The stop codon moves into the A site 2.A releasing factor binds to the stop codon in the A site 3.Separation
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True or False? All genes code for polypeptides
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False
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Where does mRNA travel to be translated into a polypeptide?
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From the nucleus to the cytoplasm
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What is necessary for transcription to occur?
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A DNA template Nucleoside Triphosphates RNA polymerase
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Why are RNA polymerases called processive?
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A single enzyme-template binding event results in the polymerization of hundreds of RNA nucleotides
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True or False? RNA polymerases do not require a primer
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True
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Where does transcription begin?
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At the transcription initiation site in the promoter
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During elongation, RNA reads the template strand in what direction?
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3'-to-5'
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RNA polymerase adds new nucleotides to what end of the growing DNA strand?
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3'
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What are coding regions?
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Sequences within a DNA molecule that are expressed as proteins.
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Where does transcription and translation occur in prokaryotes and eukaryotes?
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In prokaryotes, they occur at the same time in the cytoplasm In eukaryotes, transcription occurs in the nucleus and translation in the cytoplasm
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What is different in the gene structure of prokaryotes and eukaryotes?
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Prokaryotes transcribed regions are not interrupted by introns Eukaryotes transcribed regions are often interrupted by non-coding introns
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What is the difference of modification of mRNA after initial transcription but before translation in prokaryotes and eukaryotes?
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In prokaryotes there is none In eukaryotes introns gets spliced out; 5' cap and 3' poly A tail are added
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How can you locate introns within a eukaryotic gene?
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Nucleic acid hybridization
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What removes introns and splices the exons together?
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RNA splicing
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What are consensus sequences?
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Short stretches of DNA that appear with little variation in many different genes. At the boundaries between introns and exons
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As soon as the pre-mRNA is transcribed, the consensus sequences are bound by what?
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Several small nuclear ribonucleoprotein particles (snRNPs)
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What is the 5' cap?
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A chemically modified molecule of GTP that is added to the 5' end of pre-mRNA. It facilitates the binding of mRNA to the ribosome for translation, and it protects the mRNA from being digested by ribonucleases (enzymes that break down RNA)
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What is a poly A tail?
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It is added to the 3' end of the pre-mRNA at the end of transcription and assists in the export of the mRNA from the nucleus and is important for stability
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The translation of the nucleotide sequence of an mRNA into the amino acid sequence of a polypeptide occurs where?
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At the ribosome
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When do silent mutations occur?
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They occur because of the redundancy of the genetic code
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What are missense mutations?
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A point mutation that results in a change in the amino acid sequence
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What are nonsense mutations?
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They result in a premature stop codon
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What are frame-shift mutations?
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They result from the insertion or deletion of one or more base pairs within the coding sequence.
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When it is carrying an amino acid, the tRNA is said to be what?
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Charged
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What are aminoacyl-tRNA synthetases?
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A family of enzymes that is specific for one amino acid and for its corresponding tRNA. The reaction uses ATP.
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What is a signal sequence?
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A short stretch of amino acids that indicates where in the cell the polypeptide belongs
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What is proteolysis?
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Cutting of a polypeptide chain.
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What is glycosylation?
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The addition of carbohydrates to proteins to form glycoproteins.
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What is phosphorylation catalyzed by?
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Protein kinases