DNA Structure Overview
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Questions and Answers

Which characteristic distinguishes DNA from RNA?

  • DNA is double stranded, while RNA is single stranded. (correct)
  • DNA contains ribose instead of deoxyribose.
  • DNA only contains purines as its nitrogenous bases.
  • DNA is composed of one type of nitrogenous base only.

    • What type of bond links the nitrogenous base to the sugar in a nucleotide?

  • Glycosidic linkage (correct)
  • Peptide bond
  • Hydrogen bond
  • Phosphodiester bond

    • What is the role of phosphodiester bonds in DNA?

  • They connect the nitrogenous bases to the deoxyribose sugar.
  • They stabilize the double helix structure of DNA.
  • They join the 3’-hydroxyl group of one nucleotide to the 5’-hydroxyl group of another. (correct)
  • They create hydrogen bonds between complementary base pairs.

    • Which of the following accurately describes Chargaff's rule?

    <p>The percentage of Cytosine equals that of Guanine in DNA.</p> Signup and view all the answers

    Which statement about nucleoside triphosphates is true?

    <p>They consist of a sugar, a nitrogenous base, and three phosphate groups.</p> Signup and view all the answers

    What type of bonds hold the two strands of DNA together?

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

    Which nitrogenous bases pair together in DNA?

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

    What is the significance of the major and minor grooves in the DNA double helix?

    <p>They provide space for binding of regulatory proteins.</p> Signup and view all the answers

    What is Chargaff's rule regarding nucleotide composition in double-stranded DNA?

    <p>A = T and G = C</p> Signup and view all the answers

    What happens during the denaturation of DNA?

    <p>The hydrogen bonds between paired bases are disrupted.</p> Signup and view all the answers

    What type of DNA exhibits lower melting temperatures due to its base composition?

    <p>A+T-rich DNA</p> Signup and view all the answers

    What structural feature of DNA contributes to its antiparallel arrangement?

    <p>Orientation of the sugar-phosphate backbone</p> Signup and view all the answers

    Study Notes

    DNA Structure

    • DNA is a double-stranded molecule (dsDNA).
    • The two strands are held together by hydrogen bonds through complementary base pairing.
    • Guanine (G) pairs with cytosine (C) forming three hydrogen bonds.
    • Adenine (A) pairs with thymine (T) forming two hydrogen bonds.
    • The DNA sequence is a primary structure, and the DNA helix is a secondary structure.
    • DNA strands run in opposite directions (antiparallel).
    • The 3' end of DNA has a hydroxyl group at the 3' position on the deoxyribose sugar.
    • The 5' end of DNA has a phosphate group at the 5' position on the deoxyribose sugar.
    • DNA exists in different forms: B-form, A-form, and Z-form.
    • The B-form is a right-handed helix with 10 base pairs (bps) per 360° turn.
    • The A-form has 11 bps per 360° turn and the bases tilted 20° from perpendicular.
    • The Z-form is a left-handed helix with 12 bps per turn.
    • The transition between B and Z forms may affect gene expression regulation.
    • The hydrophilic deoxyribose-phosphate backbones are on the outside of the helix.
    • The hydrophobic bases are stacked in the interior.
    • The spatial relationship between the strands creates major and minor grooves.
    • Each helical turn is separated by 0.34 nanometers.

    Nucleotides

    • Nucleotides are the building blocks of DNA and RNA.
    • Each nucleotide has three components: a nitrogenous base, a pentose sugar, and a phosphate group.
    • DNA nucleotides contain deoxyribose sugar, while RNA nucleotides contain ribose sugar.
    • DNA has thymine (T), while RNA has uracil (U).
    • DNA is a polymer of deoxynucleoside monophosphates (dNMPs).
    • RNA is a polymer of nucleoside monophosphates (NMPs).
    • Purines are adenine (A) and guanine (G) (two rings).
    • Pyrimidines are cytosine (C), thymine (T), and uracil (U) (one ring).

    Chargaff's Rule

    • In double-stranded DNA:
      • The amount of adenine (A) equals the amount of thymine (T).
      • The amount of guanine (G) equals the amount of cytosine (C).
      • The total amount of purines (A + G) equals the total amount of pyrimidines (T + C).

    Denaturation

    • Denaturation occurs when hydrogen bonds between complementary bases are disrupted.
    • This process can happen under specific lab conditions (pH change, high temperatures).
    • Tm (Melting Temperature) is the temperature at which half of the helical structure in DNA becomes single stranded.
    • DNA with a higher proportion of AT base pairs has a lower Tm compared to GC-rich DNA.

    Quiz Question

    • If adenine = 30%, the percentage of guanine will be 20% (since G always pairs with C, and A with T).

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    DNA Structure Lecture Notes PDF

    Description

    This quiz explores the fundamental structure of DNA, focusing on its double-stranded nature, base pairing, and the various forms such as B, A, and Z. Understand the significance of antiparallel strands and how structural differences can influence gene expression. Perfect for students studying molecular biology.

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