DNA and RNA Composition and Structure
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Questions and Answers

Which of the following nitrogenous bases are purines found in DNA?

  • Cytosine
  • Guanine (correct)
  • Adenine (correct)
  • Thymine

    • What is the main structural difference between a nucleoside and a nucleotide?

  • Nucleotides are larger than nucleosides due to additional nitrogenous bases.
  • Nucleotide sugar can only be ribose, while nucleosides contain deoxyribose.
  • Nucleosides contain a sugar and a nitrogenous base, while nucleotides contain a sugar, a nitrogenous base, and a phosphate group. (correct)
  • Nucleosides include a phosphate group, and nucleotides do not.

    • Which sugar is included in DNA nucleotides?

  • Glucose
  • Fructose
  • Ribose
  • Deoxyribose (correct)

    • What is the primary function of the phosphate group in nucleotides?

    <p>To stabilize the structure of nucleic acids</p> Signup and view all the answers

    What type of sugar is found in DNA nucleotides?

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

    Which of the following statements is true regarding the nitrogenous bases in DNA?

    <p>The nitrogenous bases are weakly basic and can form positive charges.</p> Signup and view all the answers

    Which nitrogenous base is found in RNA but not in DNA?

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

    What type of bond connects nucleotides in a DNA polynucleotide chain?

    <p>Phosphodiester bonds</p> Signup and view all the answers

    What is contained in a nucleoside?

    <p>A sugar and a nitrogenous base</p> Signup and view all the answers

    Which nucleotide pairing has the stronger bond in DNA?

    <p>Cytosine and Guanine</p> Signup and view all the answers

    What type of nitrogenous bases are cytosine and thymine classified as?

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

    What is the overall charge of DNA and why?

    <p>Negative due to the phosphate group</p> Signup and view all the answers

    In which direction do the two strands of DNA run?

    <p>Antiparallel, one 5' to 3', the other 3' to 5'</p> Signup and view all the answers

    What is the structural shape of DNA?

    <p>Double helix</p> Signup and view all the answers

    What is the role of nucleoside analogs like AZT in viral infections?

    <p>Inhibiting viral DNA synthesis</p> Signup and view all the answers

    Which pairing of bases occurs in DNA?

    <p>Thymine pairs with Adenine</p> Signup and view all the answers

    Which of these best describes the role of histones in DNA packaging?

    <p>They provide structural support by winding DNA to form nucleosomes.</p> Signup and view all the answers

    How does the presence of uracil in RNA differ from thymine's role in DNA?

    <p>Uracil replaces thymine as a pyrimidine base in RNA.</p> Signup and view all the answers

    What is the key distinction between heterochromatin and euchromatin concerning gene expression?

    <p>Euchromatin is more accessible to transcription machinery, therefore more actively transcribed, whereas heterochromatin is tightly packed and less transcribed.</p> Signup and view all the answers

    If a strand of DNA includes the sequence 5’-GCTAT-3’, what would be its complementary strand?

    <p>3’-CGATA-5’</p> Signup and view all the answers

    How do nucleoside analogs like AZT interfere with viral replication?

    <p>They become incorporated into the viral genome, causing chain termination.</p> Signup and view all the answers

    Transcription describes the process by which a DNA sequence is used to synthesize which type of molecule?

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

    The process where tRNA interacts with mRNA to build a specific amino acid chain is typically called

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

    What role does acetylation of histones play in gene expression?

    <p>It opens up the chromatin structure, promoting gene expression.</p> Signup and view all the answers

    Which of the following best describes the relationship between a nucleoside and a nucleotide?

    <p>A nucleotide is a nucleoside with an added phosphate group.</p> Signup and view all the answers

    How many hydrogen bonds are formed between guanine and cytosine in a DNA molecule?

    <p>3</p> Signup and view all the answers

    If a segment of DNA has the sequence 5'-ATGC-3' on one strand, what would be the sequence of the complementary strand?

    <p>3'-CGTA-5'</p> Signup and view all the answers

    What is the primary role of histone proteins in DNA packaging?

    <p>To compact and organize DNA into nucleosomes</p> Signup and view all the answers

    What is the primary function of histone proteins within a cell?

    <p>To compact and organize DNA.</p> Signup and view all the answers

    Which of the following best describes heterochromatin?

    <p>Highly condensed DNA, transcriptionally inactive</p> Signup and view all the answers

    Which structural feature stabilizes the double helix of DNA, in addition to hydrogen bonds?

    <p>Van der Waals interactions and hydrophobic properties of the bases</p> Signup and view all the answers

    Why are nucleoside analogs used in antiviral treatments such as AZT and acyclovir?

    <p>They replace natural nucleosides, causing chain termination.</p> Signup and view all the answers

    What is the effect of histone acetylation on DNA?

    <p>It decreases the electrostatic attraction between histones and DNA, leading to increased gene expression</p> Signup and view all the answers

    How does the structure of a DNA molecule contribute to its function in storing genetic information?

    <p>The specific base pairing and the double helical structure.</p> Signup and view all the answers

    What is the role of histone deacetylases?

    <p>To remove acetyl groups from histones, which decreases gene expression</p> Signup and view all the answers

    What are the repeating units that comprise chromatin?

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

    Which nitrogenous base is present in RNA but not in DNA?

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

    What is a key structural difference between RNA and DNA?

    <p>RNA has a ribose sugar, while DNA has a deoxyribose sugar</p> Signup and view all the answers

    How does the phosphate group contribute to the function of a nucleotide?

    <p>It gives the nucleotide a negative charge important for stability and function.</p> Signup and view all the answers

    What distinguishes Z-DNA from B-DNA?

    <p>Z-DNA is a left-handed helix, while B-DNA is right-handed.</p> Signup and view all the answers

    The formation of what type of structures are primarily responsible for the three-dimensional folding of RNA?

    <p>Secondary structure</p> Signup and view all the answers

    Where does the process of DNA compaction using histones and nucleosome formation primarily occur?

    <p>Cell nucleus</p> Signup and view all the answers

    Which of the following best describes the role of messenger RNA (mRNA)?

    <p>To carry the genetic code for proteins, to the cytoplasm</p> Signup and view all the answers

    What type of bond connects nucleotides along a strand of DNA?

    <p>Phosphodiester bonds</p> Signup and view all the answers

    Which type of RNA is a component of ribosomes?

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

    Which of the following statements best describes the antiparallel nature of the DNA double helix?

    <p>One strand is oriented 5' to 3' while the complementary strand is 3' to 5'.</p> Signup and view all the answers

    What is the function of transfer RNA (tRNA)?

    <p>To carry amino acids to the ribosome during translation</p> Signup and view all the answers

    What is the anticodon region of tRNA responsible for?

    <p>Binding to specific mRNA codons.</p> Signup and view all the answers

    What is the role of supercoiling in DNA packaging?

    <p>To help minimize the space occupied by the DNA</p> Signup and view all the answers

    Why is the ratio of A to T and G to C consistent within a DNA molecule?

    <p>Because hydrogen bonding only occurs between those specific pairs.</p> Signup and view all the answers

    Which of the following is a direct result of the removal of acetyl groups from lysine residues of histones?

    <p>A more compact chromatin structure.</p> Signup and view all the answers

    What is the role of aminoacyl-tRNA synthetase enzymes?

    <p>To attach specific amino acids to their corresponding tRNA molecules</p> Signup and view all the answers

    Which of the following is NOT a function of the RNA molecule?

    <p>To permanently store the genetic information of the cell.</p> Signup and view all the answers

    In the context of RNA structure, what are hairpin loops, stem-loops, bulges, and internal loops?

    <p>Structural features formed due to base pairing within the RNA molecule.</p> Signup and view all the answers

    Study Notes

    DNA and RNA Composition and Structure

    • Nitrogenous Bases: DNA contains two groups:
      • Pyrimidines: Cytosine, Thymine; aromatic molecules with two nitrogens in the ring.
      • Purines: Adenine, Guanine; aromatic, with a pyrimidine ring fused to an imidazole ring.
      • These bases are weakly basic.
    • Nucleotide Structure:
      • Nucleoside: A nitrogenous base and a sugar (no phosphate).
        • Sugar is deoxyribose in DNA and ribose in RNA.
        • This combination forms the nucleoside; building blocks of nucleic acids.
      • Nucleotide: A nucleoside with a phosphate group.
        • The phosphate group gives the nucleotide a negative charge.
        • Essential structural and functional unit of nucleic acids (DNA and RNA).
    • DNA Polynucleotide Chain: DNA nucleotides are linked by phosphodiester bonds, forming a phosphate backbone.
      • This arrangement gives DNA an overall negative charge.
    • Nucleotide Base Pairing:
      • Adenine pairs with Thymine via two hydrogen bonds (A-T).
      • Guanine pairs with Cytosine via three hydrogen bonds (G-C).
      • The specificity of these pairings maintains the DNA's double-stranded nature.
    • Double-Stranded DNA: The two DNA strands run antiparallel (5' to 3' and 3' to 5').
    • Double Helix: DNA forms a double helix, stabilized by:
      • Hydrogen bonds between base pairs.
      • Van der Waals interactions.
      • Hydrophobic interactions among the bases.
      • This arrangement can occur in different forms (e.g., B-DNA, A-DNA, Z-DNA).
    • Nucleoside Analogs: Some analogs, like AZT and acyclovir, can block viral DNA synthesis by substituting natural nucleosides and causing chain termination.

    DNA Packaging and Chromatin

    • DNA Packaging in the Nucleus: DNA is packaged by winding around histone proteins to form nucleosomes.
      • Nucleosomes are further compacted into solenoids and chromatin structures.
      • Histones are small, positively charged proteins involved in DNA compaction.
    • Histones and Chromatin: Nucleosomes consist of DNA wrapped around histone protein cores.
      • Chromatin exists in two forms:
        • Heterochromatin: Highly condensed, transcriptionally inactive.
        • Euchromatin: Less condensed, more gene expression.
    • Histone Modifications:
      • Acetylation: Weakening the bond between histones and DNA, leading to higher gene expression.
      • Deacetylation: Increasing the bond between histones and DNA, leading to lower gene expression.

    RNA Types and Functions

    • RNA Types:
      • mRNA (messenger RNA): Encodes proteins, contains the nucleotide sequence for translation.
      • rRNA (ribosomal RNA): Structural component of ribosomes, involved in protein synthesis.
      • tRNA (transfer RNA): Delivers amino acids for protein synthesis; anticodon region recognizes mRNA codons, amino acid attachment site.
      • Other RNAs: RNA primers, small nuclear RNAs, microRNAs, also have regulatory roles.
      • Eukaryotic ribosomes contain four types of rRNA (18S, 28S, 5S, 5.8S) packaged with proteins into two subunits (60S and 40S).
      • RNA typically exists as a single-stranded molecule that can fold on itself.

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    Description

    This quiz explores the intricate composition and structure of DNA and RNA, focusing on nitrogenous bases, nucleotides, and polynucleotide chains. Test your knowledge on base pairing and the unique properties of these essential biomolecules.

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