RNA Structure and Function Quiz
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Questions and Answers

What type of RNA does RNA polymerase I primarily transcribe?

  • siRNA
  • mRNA
  • tRNA
  • rRNA (correct)

    • How does α-amanitin affect RNA polymerase II activity?

  • It activates additional polymerase enzymes.
  • It enhances the transcription rate.
  • It inhibits transcription by obstructing the enzyme. (correct)
  • It has no effect on RNA synthesis.

    • Which statement accurately describes the role of RNA polymerase III?

  • It only transcribes large RNA molecules.
  • It transcribes pre-mRNA and snoRNA.
  • It is involved in ribosome assembly.
  • It transcribes tRNA and small rRNA. (correct)

    • What is the first step in the transcription process?

    <p>Initiation (A)</p> Signup and view all the answers

    What commonly occurs during the elongation stage of transcription?

    <p>The DNA is unwound and nucleotides are added. (C)</p> Signup and view all the answers

    Which RNA polymerase is responsible for transcribing siRNAs linked to DNA methylation?

    <p>RNA polymerase V (A)</p> Signup and view all the answers

    Why are RNA polymerases considered multimeric enzymes?

    <p>They contain multiple subunits linked together. (C)</p> Signup and view all the answers

    During the termination phase of transcription, what is recognized?

    <p>The end of the transcription unit. (C)</p> Signup and view all the answers

    What indicates that the 'tree trunks' in the transcription model represent DNA molecules?

    <p>The addition of deoxyribonuclease (D)</p> Signup and view all the answers

    Which strand of DNA serves as the template for RNA synthesis during transcription?

    <p>The template strand (B)</p> Signup and view all the answers

    What role does the promoter play in transcription?

    <p>It indicates the DNA strand to be transcribed (A)</p> Signup and view all the answers

    How do RNA transcripts differ from the DNA template strand?

    <p>They contain U instead of T (A)</p> Signup and view all the answers

    What is essential for recognizing a transcription unit?

    <p>Presence of a promoter (A)</p> Signup and view all the answers

    Which statement about transcription units is accurate?

    <p>They contain a promoter, RNA-coding region, and a terminator. (A)</p> Signup and view all the answers

    What happens to the RNA molecules as the transcription apparatus progresses along the DNA?

    <p>They lengthen as more RNA is synthesized. (C)</p> Signup and view all the answers

    What does the transcription apparatus rely on to know where to start and stop transcription?

    <p>Encoded information in the DNA sequence (A)</p> Signup and view all the answers

    What determines which strand of DNA will serve as the template for transcription?

    <p>The orientation and spacing of consensus sequences (A)</p> Signup and view all the answers

    What occurs during abortive initiation in RNA synthesis?

    <p>Short RNA transcripts of 2 to 6 nucleotides are produced and released. (B)</p> Signup and view all the answers

    What happens to RNA polymerase after the initiation of transcription?

    <p>It changes conformation and can no longer bind to the promoter. (B)</p> Signup and view all the answers

    How is transcription initiated in terms of nucleotide pairing?

    <p>RNA polymerase pairs bases at the start site with complementary bases on the DNA template strand. (B)</p> Signup and view all the answers

    What characteristic do initial RNA molecules possess at their 5’ end?

    <p>Three phosphate groups (C)</p> Signup and view all the answers

    What is the average rate of nucleotide addition by RNA polymerase in bacterial cells at 37°C?

    <p>40 nucleotides per second (A)</p> Signup and view all the answers

    What happens to the sigma factor after the initiation of transcription?

    <p>It is typically released after initiation. (C)</p> Signup and view all the answers

    Which of the following is NOT involved in the process of transcription initiation?

    <p>Binding of a primer before RNA synthesis begins (D)</p> Signup and view all the answers

    What are the two basic functions that living organisms must perform?

    <p>Store genetic information and catalyze chemical reactions (D)</p> Signup and view all the answers

    What discovery in 1981 contributed to resolving the dilemma of the origin of life regarding proteins and nucleic acids?

    <p>The existence of ribozymes as biological catalysts (C)</p> Signup and view all the answers

    What is a ribozyme?

    <p>A catalytic RNA molecule (B)</p> Signup and view all the answers

    Why is RNA believed to have been the original genetic material rather than DNA?

    <p>RNA can function both in information storage and as a catalyst (B)</p> Signup and view all the answers

    What transition is suggested to have occurred as life evolved from an RNA world?

    <p>Proteins took over most catalytic functions from RNA (C)</p> Signup and view all the answers

    How did ribozymes contribute to the early evolution of life on Earth?

    <p>By catalyzing the formation of protein-based enzymes (B)</p> Signup and view all the answers

    What characteristics of DNA made it a better choice than RNA as the primary carrier of genetic information?

    <p>DNA has greater chemical stability and faithful replication (D)</p> Signup and view all the answers

    When are self-replicating ribozymes believed to have first arisen?

    <p>Between 3.5 billion and 4 billion years ago (D)</p> Signup and view all the answers

    What is true about archaeal RNA polymerase compared to bacterial RNA polymerase?

    <p>Archaeal RNA polymerase is more complex than bacterial RNA polymerase. (C)</p> Signup and view all the answers

    Which statement best describes the TATA box in archaea?

    <p>It serves a similar function to the TATA box in eukaryotic promoters. (C)</p> Signup and view all the answers

    What distinguishes the transcription factors in archaea from those in bacteria?

    <p>TBP is found in archaea but not in bacteria. (D)</p> Signup and view all the answers

    What evidence supports the close relationship between archaea and eukaryotes?

    <p>Both groups produce histone proteins which compact DNA. (D)</p> Signup and view all the answers

    How do the transcription processes in archaea compare to those in bacteria?

    <p>Some transcription regulators in archaea are similar to those in bacteria. (D)</p> Signup and view all the answers

    What is the primary function of topoisomerase enzymes during transcription?

    <p>To relieve stress from unwinding DNA (A)</p> Signup and view all the answers

    How many nucleotides of RNA are typically paired with the DNA template at any one time during transcription?

    <p>8 to 10 (B)</p> Signup and view all the answers

    What phenomenon can cause RNA polymerase to pause during transcription?

    <p>Formation of secondary structures (D)</p> Signup and view all the answers

    Which mechanism is NOT mentioned as a way to minimize backtracking during transcription?

    <p>Addition of exogenous nucleotides (D)</p> Signup and view all the answers

    What is the effect of transcriptional pausing on RNA synthesis?

    <p>It decreases the synthesis rate (C)</p> Signup and view all the answers

    What role does backtracking play in the process of transcription?

    <p>It serves as a proofreading mechanism (B)</p> Signup and view all the answers

    What is the synthesis rate of RNA compared to the synthesis rate of DNA in bacterial cells?

    <p>Lower than DNA synthesis (D)</p> Signup and view all the answers

    What does RNA polymerase exhibit while incorporating nucleotides into the RNA chain?

    <p>Proofreading capabilities (C)</p> Signup and view all the answers

    What characteristic of RNA allows it to serve as both a genetic information carrier and a catalyst?

    <p>RNA's capability to form ribozymes (C)</p> Signup and view all the answers

    What role did ribozymes likely play in the early evolution of life?

    <p>They catalyzed reactions necessary for self-replication. (A)</p> Signup and view all the answers

    Why is RNA considered to have preceded DNA in early life forms?

    <p>RNA can act as an enzyme as well as store genetic information. (C)</p> Signup and view all the answers

    What significant change occurred as life evolved from an RNA world to the current genetic system?

    <p>Proteins took on more catalyst functions. (B)</p> Signup and view all the answers

    Which statement about self-replicating ribozymes is accurate?

    <p>They likely initiated the process of life on Earth. (D)</p> Signup and view all the answers

    What potentially limited the role of RNA as life evolved?

    <p>The introduction of DNA as a more stable genetic material. (A)</p> Signup and view all the answers

    Which function does not align with the abilities of ribozymes?

    <p>Synthesizing DNA strands. (B)</p> Signup and view all the answers

    What dilemma arises from the relationship between nucleic acids and proteins?

    <p>Both require each other for their existence. (A)</p> Signup and view all the answers

    What is the primary role of long noncoding RNAs (lncRNAs) in eukaryotic cells?

    <p>To regulate gene expression (D)</p> Signup and view all the answers

    Which components are necessary for the transcription process to occur?

    <p>A DNA template, raw materials, and a transcription apparatus (B)</p> Signup and view all the answers

    How does the process of transcription differ from DNA replication?

    <p>Transcription only selectively synthesizes parts of the DNA molecule (D)</p> Signup and view all the answers

    What was demonstrated by Oscar Miller Jr. and colleagues using electron microscopy?

    <p>RNA is transcribed from a DNA template (A)</p> Signup and view all the answers

    What issue does the selective transcription of genes aim to address in cellular processes?

    <p>Wasting energy by synthesizing unnecessary RNA (D)</p> Signup and view all the answers

    What type of system has been discovered in prokaryotes that resembles RNA interference?

    <p>CRISPR RNA (crRNA) system (D)</p> Signup and view all the answers

    Which of the following best describes the efficiency of gene transcription in cells?

    <p>Transcription is highly selective and occurs as needed (A)</p> Signup and view all the answers

    What do the 'Christmas-tree-like structures' observed in the electron microscopy study represent?

    <p>RNA molecules being synthesized (C)</p> Signup and view all the answers

    What denotes the -35 consensus sequence in bacterial promoters?

    <p>A specific sequence termed TTGACA located about 35 nucleotides upstream (A)</p> Signup and view all the answers

    What happens when mutations occur within the -10 and -35 consensus sequences?

    <p>They reduce the rate of transcription, termed down mutations. (C)</p> Signup and view all the answers

    Which structure is formed when the sigma factor associates with core RNA polymerase?

    <p>Holoenzyme (C)</p> Signup and view all the answers

    What is the significance of the upstream element in bacterial promoters?

    <p>Contains sequences that may enhance transcription initiation (D)</p> Signup and view all the answers

    At which positions does unwinding of DNA begin during transcription initiation?

    <p>From -10 to +2 (B)</p> Signup and view all the answers

    What type of mutations can occasionally increase the rate of transcription?

    <p>Up mutations (B)</p> Signup and view all the answers

    What is the role of proteins binding to sequences in and near the promoter?

    <p>They can either stimulate or repress the rate of transcription. (C)</p> Signup and view all the answers

    How far does the holoenzyme extend from the promoter upon binding?

    <p>From -50 to +20 (C)</p> Signup and view all the answers

    What happens when RNA polymerase incorporates a mismatched nucleotide during transcription?

    <p>It backtracks and cleaves the last two nucleotides. (A)</p> Signup and view all the answers

    During transcription termination, which sequence feature leads to the pausing of RNA polymerase?

    <p>The sequence of the terminator itself. (D)</p> Signup and view all the answers

    What characterizes Rho-dependent terminators?

    <p>They require a specific sequence called the rut site. (B)</p> Signup and view all the answers

    What happens to RNA polymerase upon reaching a terminator sequence?

    <p>It stops synthesizing RNA, and the RNA dissociates. (A)</p> Signup and view all the answers

    What is a common feature shared by Rho-independent terminators?

    <p>They contain inverted repeats of nucleotides. (B)</p> Signup and view all the answers

    How does the rho factor contribute to transcription termination?

    <p>It unwinds the DNA-RNA hybrid complex. (B)</p> Signup and view all the answers

    Why do most terminators not immediately stop transcription at their location?

    <p>Transcription stops after the entire terminator has been transcribed. (A)</p> Signup and view all the answers

    What is one characteristic that distinguishes Rho-dependent from Rho-independent terminators?

    <p>The specific binding site for the rho factor. (A)</p> Signup and view all the answers

    What determines the direction of transcription in a DNA strand?

    <p>The orientation and spacing of consensus sequences (D)</p> Signup and view all the answers

    What is the outcome of the abortive initiation process in RNA synthesis?

    <p>Short transcripts of 2 to 6 nucleotides are generated and released (D)</p> Signup and view all the answers

    How does RNA polymerase begin the synthesis of an RNA molecule?

    <p>By pairing the base of the first nucleotide with its complementary DNA base (B)</p> Signup and view all the answers

    What happens to the RNA polymerase after the initiation phase of transcription?

    <p>It transitions to the elongation stage and cannot re-bind to the promoter (B)</p> Signup and view all the answers

    What is a characteristic of the initial RNA molecule at its 5’ end?

    <p>It has three phosphate groups remaining (B)</p> Signup and view all the answers

    What typically occurs in bacterial cells during the elongation phase of transcription?

    <p>Nucleotides are added at a rate of about 40 per second (A)</p> Signup and view all the answers

    What initiates the transition from initiation to the elongation stage for RNA polymerase?

    <p>The synthesis of RNA between 9 to 12 nucleotides (B)</p> Signup and view all the answers

    What is the role of consensus sequences in the transcription process?

    <p>They guide RNA polymerase to the correct start site (D)</p> Signup and view all the answers

    Which RNA polymerase transcribes pre-mRNAs and some miRNAs?

    <p>RNA polymerase II (A)</p> Signup and view all the answers

    What is the primary impact of α-amanitin on eukaryotic cells?

    <p>It inhibits RNA polymerase II activity. (C)</p> Signup and view all the answers

    During which stage of transcription does RNA polymerase add nucleotides to the growing RNA strand?

    <p>Elongation (C)</p> Signup and view all the answers

    Which RNA polymerase is responsible for producing tRNA molecules?

    <p>RNA polymerase III (B)</p> Signup and view all the answers

    What describes the composition of eukaryotic RNA polymerases?

    <p>They are large multimeric enzymes. (B)</p> Signup and view all the answers

    What happens during the termination stage of transcription?

    <p>The RNA molecule separates from the DNA template. (D)</p> Signup and view all the answers

    Which of the following roles does RNA polymerase IV perform?

    <p>Transcribes siRNAs that silence transposons (C)</p> Signup and view all the answers

    What is a key feature of the elongation phase during transcription?

    <p>DNA is unwound and threaded through RNA polymerase. (D)</p> Signup and view all the answers

    Study Notes

    • RNA is crucial for life, acting as both a genetic material carrier and a catalyst for chemical transformations.
    • RNA, a polymer of nucleotides, differs from DNA in its structure:
      • RNA uses ribose sugar, while DNA has deoxyribose.
      • RNA contains uracil instead of thymine.
      • RNA is usually single-stranded, while DNA is double-stranded.
    • RNA molecules fold into complex secondary structures that affect their functions.
    • RNA performs diverse functions in cells:
      • Ribosomal RNA (rRNA) composes ribosomes (protein synthesis sites).
      • Messenger RNA (mRNA) carries genetic instructions to ribosomes.
      • Transfer RNA (tRNA) facilitates amino acid incorporation into proteins.
      • Other types include small nuclear RNA (snRNA), microRNA (miRNA), small interfering RNA (siRNA), and more, including CRISPR RNA (crRNA), Piwi-interacting RNA (piRNA), and long non-coding RNA (IncRNA).
    • Transcription, the process of producing RNA from a DNA template, has three major stages:
      • Initiation: RNA polymerase recognizes and binds to the promoter region of a gene, involving promoter recognition, a transcription bubble, and initial RNA bonds.
      • Elongation: RNA polymerase unwinds DNA and adds nucleotides to a growing RNA strand, often with temporary pausing determined by RNA or DNA characteristics, or by DNA structure like nucleosomes.
      • Termination: RNA polymerase signals to stop transcribing, involving specific terminator sequences (rho-dependent or rho-independent).
    • Bacteria typically contain one RNA polymerase type that transcribes all RNA types, typically a core enzyme plus a sigma factor.
    • Eukaryotes contain three RNA polymerases, each with specific functions and target genes, with different promoters.
    • DNA template strand is copied into a complementary RNA strand during transcription.
    • Promoters in DNA specify transcription start sites.
    • Bacterial promoters frequently contain conserved sequences, including the -10 and -35 regions (consensus sequences).
    • Eukaryotic promoters have a core promoter region containing various consensus sequences, typically near the transcription initiation site (such as the TATA box), and upstream regulatory promoter regions, involving additional transcription factors.
    • Eukaryotic RNA polymerase and general transcription factors work together to initiate transcription, involving multiple transcription factors such as TFIID (with the TBP subunit).
    • Transcription in archaea shares features with both bacterial and eukaryotic transcription, involving similar mechanisms for initiation, elongation, and termination and certain similarities in promoter structure and transcription factors.
    • RNA polymerase structure, promoter recognition, and termination mechanisms vary among bacterial, archaeal, and eukaryotic systems.
    • Errors occur in RNA synthesis, but proofreading mechanisms assist, particularly in the case of RNA polymerase.
    • Termination of transcription in bacteria involves rho-dependent and rho-independent terminators.
    • Eukaryotic cells show varied termination sequences for specific RNA polymerases depending on type.
    • RNA polymerases can produce short transcripts before fully elongated.
    • Transcriptional initiation and termination involves specific sequences and factors.
    • Nucleosome structure and modifications are important to access DNA during eukaryotic transcription.

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