Genome and Chromosome Structure Quiz
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Questions and Answers

What characterizes highly repetitive sequences in the genome?

  • They include functional sequences like rRNA genes.
  • They have a single copy in the genome.
  • They are involved in gene regulation.
  • They contain multiple copies, such as satellite DNA. (correct)

    • Which type of supercoiling aids in DNA replication and transcription?

  • Looped domain organization
  • Positive supercoiling
  • Negative supercoiling (correct)
  • Nucleosome formation

    • What defines constitutive heterochromatin?

  • It is located in actively transcribed regions of the genome.
  • It is always condensed and found in centromeres. (correct)
  • It can change locations within the genome.
  • It is less condensed and transcriptionally active.

    • Which process organizes bacterial chromosomes into microdomains?

    <p>NAP-mediated folding</p> Signup and view all the answers

    In the context of eukaryotic chromosomes, what is euchromatin?

    <p>It is less condensed and transcriptionally active.</p> Signup and view all the answers

    What structure is formed by DNA wrapped around histone proteins?

    <p>Nucleosome</p> Signup and view all the answers

    Which type of chromatin can vary in its state of condensation?

    <p>Facultative heterochromatin</p> Signup and view all the answers

    What is the role of Topoisomerase I in DNA compaction?

    <p>To relax positive supercoiling.</p> Signup and view all the answers

    What is the primary function of Alu elements within the genome?

    <p>They act as tandem repeats in moderately repetitive sequences.</p> Signup and view all the answers

    What is the final level of chromatin structure in the compaction hierarchy?

    <p>Heterochromatin</p> Signup and view all the answers

    Which model of DNA replication allows both parental and daughter strands to be mixed together?

    <p>Dispersive model</p> Signup and view all the answers

    What initiates the DNA replication process in E. coli?

    <p>DnaA proteins binding to DnaA box sequences</p> Signup and view all the answers

    In eukaryotic transcription, which factor is primarily involved in recognizing the TATA box during initiation?

    <p>Transcription factors like TFIID</p> Signup and view all the answers

    What mechanism does telomerase perform to address the chromosome end problem in eukaryotes?

    <p>Adds repetitive sequences to telomeres</p> Signup and view all the answers

    Which RNA polymerase is responsible for synthesizing mRNA in eukaryotes?

    <p>RNA Polymerase II</p> Signup and view all the answers

    What occurs during the splicing of hnRNA to form mature mRNA?

    <p>Introns are removed and exons are joined</p> Signup and view all the answers

    What is the role of the Shine-Dalgarno sequence in bacterial translation?

    <p>It helps in ribosomal binding to mRNA</p> Signup and view all the answers

    Which step in DNA replication is specifically performed by DNA Polymerase I?

    <p>Filling in gaps after RNA primers are removed</p> Signup and view all the answers

    Which hypothesis regarding genes was initially proposed by Garrod?

    <p>Inborn error of metabolism</p> Signup and view all the answers

    What does the Wobble Hypothesis imply about tRNAs?

    <p>Fewer tRNAs are needed due to base-pairing flexibility</p> Signup and view all the answers

    What characteristic of the C-Value Paradox highlights a discrepancy in organism genetics?

    <p>Genome size does not correlate with organism complexity.</p> Signup and view all the answers

    Which type of supercoiling is induced by DNA gyrase during the process of DNA replication?

    <p>Negative supercoiling</p> Signup and view all the answers

    Which feature distinguishes facultative heterochromatin from constitutive heterochromatin?

    <p>It can change its state of compaction under certain conditions.</p> Signup and view all the answers

    In the context of bacterial chromosomes, what is the primary function of looped domains?

    <p>To compact the chromosome and organize its structure.</p> Signup and view all the answers

    What level of chromatin structure is described by the term '30 nm Fiber'?

    <p>The arrangement of nucleosomes into a compact form.</p> Signup and view all the answers

    Which type of repetitive sequence is characterized by short DNA sequences that can move within the genome?

    <p>Alu elements</p> Signup and view all the answers

    What role do NAPs play in the structure of bacterial chromosomes?

    <p>They are involved in organizing the DNA into microdomains.</p> Signup and view all the answers

    Which of the following accurately depicts the state of euchromatin compared to heterochromatin?

    <p>Euchromatin is less condensed and transcriptionally active.</p> Signup and view all the answers

    Which subunit of chromatin structure is primarily associated with the formation of nucleosomes?

    <p>Histones</p> Signup and view all the answers

    What is the main difference between negative and positive supercoiling in DNA?

    <p>Negative supercoiling unwinds the DNA, while positive induces tension in the strands.</p> Signup and view all the answers

    What occurs during the elongation phase of eukaryotic transcription?

    <p>The RNA molecule produced contains both introns and exons.</p> Signup and view all the answers

    In the context of DNA replication, what is the function of DNA ligase?

    <p>Joins Okazaki fragments on the lagging strand.</p> Signup and view all the answers

    During RNA processing, what modification occurs at the 5' end of mature mRNA?

    <p>Addition of a 5' cap for stability.</p> Signup and view all the answers

    How do chromosomes in eukaryotic cells manage the large DNA volume during replication?

    <p>Through multiple replication origins across different chromosomes.</p> Signup and view all the answers

    What is the reason for having a degenerate code in protein synthesis?

    <p>To allow for multiple codons for a single amino acid.</p> Signup and view all the answers

    What is the role of helicase during DNA replication?

    <p>To unwind the DNA double helix ahead of the replication fork.</p> Signup and view all the answers

    What distinguishes the 'one gene-one polypeptide' hypothesis from earlier theories about genes?

    <p>It emphasizes the unique contribution of each gene to a single protein product.</p> Signup and view all the answers

    Which statement accurately describes the function of the rho protein during transcription?

    <p>It leads to the termination of transcription by binding to the rut site.</p> Signup and view all the answers

    What is the significance of the Shine-Dalgarno sequence in bacterial translation?

    <p>It aids in the initiation of translation by aligning the ribosome with mRNA.</p> Signup and view all the answers

    What triggers the end of eukaryotic transcription?

    <p>The formation of a polyadenylation signal.</p> Signup and view all the answers

    Study Notes

    Genome Structure and Function

    • Genome: The complete genetic material of an organism, composed of nucleotides.
    • Transposable Elements: DNA sequences that can move within a genome ("jumping genes").
    • C-Value Paradox: Genome size does not directly correlate with organismal complexity.
    • Repetitive Sequences: Occur in various forms:
      • Highly Repetitive: Multiple copies (e.g., satellite DNA).
      • Moderately Repetitive: Functional sequences (e.g., rRNA genes).
      • Tandem Repeats: Short sequences repeated in a row (e.g., Alu elements).

    Chromosome Structure and Compaction

    • Bacterial Chromosome:
      • Compacted by supercoiling.
      • Negative Supercoiling: DNA unwound (left-handed twist), aiding replication and transcription. Achieved by DNA gyrase.
      • Positive Supercoiling: DNA overwound (right-handed twist) relaxed by topoisomerase I.
      • Looped Domains: Organized by nucleoid-associated proteins (NAPs) into micro and macrodomains.
    • Eukaryotic Chromosome:
      • Chromatin: DNA-protein complex.
        • Euchromatin: Less condensed; transcriptionally active.
        • Heterochromatin: Highly condensed; inactive.
          • Constitutive Heterochromatin: Always condensed; found at centromeres.
          • Facultative Heterochromatin: Variable condensation; location can change.

    Chromosome Compaction Steps

    • DNA Double Helix: Basic structure.
    • Nucleosome: DNA wrapped around histone proteins.
    • Zigzag/30 nm Fiber: Nucleosomes further compacted.
    • Looped Domains: Formed by CTCF and SMC proteins.
    • Heterochromatin: Compaction of loops.
    • Metaphase Chromosome: Highest compaction during cell division.

    DNA Replication Models

    • Conservative: Parental DNA stays together; daughter strands are entirely new.
    • Semi-Conservative: Each new DNA molecule has one original strand and one new strand (confirmed by Meselson-Stahl experiment).
    • Dispersive: Original and new DNA segments are interspersed within both strands.

    DNA Replication Process

    • Initiation: Begins at oriC in E.coli; DnaA proteins bind to DnaA box sequences. AT-rich regions unwind easily.
    • Unwinding: Helicase unwinds DNA; SSBPs stabilize separated strands; Topoisomerase relieves tension.
    • Primer Synthesis: Primase synthesizes short RNA primers to start DNA synthesis.
    • Elongation: DNA polymerase III extends strands, proofreading; Leading strand synthesized continuously; Lagging strand synthesized discontinuously as Okazaki fragments.
    • Primer Removal and Gap Filling: DNA polymerase I removes primers, fills gaps; DNA ligase joins Okazaki fragments.

    Challenges in Eukaryotic Replication

    • Large DNA Volume: Multiple replication origins manage the task (pulse-chase experiment).
    • Chromosome End Problem: Telomerase adds repetitive sequences to telomeres to prevent loss.

    Transcription (RNA Synthesis)

    • Overview of RNA Types:

      • mRNA: Carries genetic instructions.
      • tRNA: Transfers amino acids.
      • rRNA: Forms ribosomes.
      • snRNA: Involved in splicing.

    • Prokaryotic Transcription:

      • Initiation: RNA polymerase holoenzyme binds to promoter region (Pribnow box).
      • Elongation: Core RNA polymerase adds rNMPs.
      • Termination:
        • Rho-Independent: GC hairpin loop and U-rich sequence cause detachment.
        • Rho-Dependent: Rho protein binds, stopping transcription.

    • Eukaryotic Transcription:

      • Initiation: Transcription factors like TFIID bind promoter elements (TATA box) recruiting RNA Polymerase II.
      • Elongation: Produces hnRNA (pre-mRNA), including introns.
      • Termination: Polyadenylation signal (AAUAAA) sequence signals end; cleavage occurs downstream.

    • RNA Polymerases in Eukaryotes:

      • Polymerase I: rRNA synthesis
      • Polymerase II: mRNA synthesis
      • Polymerase III: tRNA and 5S rRNA synthesis

    hnRNA Processing (Eukaryotes)

    • Capping: 5' cap added for stability and ribosome recognition.
    • Polyadenylation: Poly-A tail added to 3' end for stability.
    • Splicing: Introns removed; exons joined by snRNPs (lariat formed).

    Gene Function and Hypotheses

    • Genes: Segments of DNA encoding instructions for making proteins.
    • Theories and Experiments:
      • Garrod: Inborn errors of metabolism link genes to enzymes.
      • Beadle and Tatum: "One gene-one enzyme" hypothesis (refined to "one gene-one polypeptide").

    Degenerate Code and Triplet Codons

    • Degenerate Code: Most amino acids have more than one codon.
    • Triplet Codons: Three nucleotides per codon; 64 combinations, enough for 20 amino acids.

    tRNA and the Wobble Hypothesis

    • tRNA: Carries amino acids to ribosomes (matching anticodons to mRNA codons).
    • Wobble Hypothesis: Flexible base pairing at the third codon position reduces the number of tRNA molecules needed.

    Translation

    • Initiation: Small ribosomal subunit binds mRNA and initiator tRNA.
      • Prokaryotes: Initiator tRNA carries N-formylmethionine; Shine-Dalgarno sequence.
      • Eukaryotes: Initiator tRNA uses 5' cap and poly-A tail.
    • Elongation: Charged tRNA enters A site; peptide bonds form (catalyzed by peptidyl transferase).
    • Termination: Release factors recognize stop codons; ribosome complex disassembles.

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    Description

    Test your knowledge on genome structure and chromosome compaction. This quiz covers essential concepts such as transposable elements, the C-value paradox, and various forms of repetitive sequences. Dive into the intricacies of bacterial and eukaryotic chromosome organization and compaction methods.

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