Nucleotide and Nucleoside Structures Quiz
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Questions and Answers

What is the diameter of the DNA helix mentioned in the text?

  • 34A
  • 10A
  • 20A (correct)
  • 36A
  • How are the planes of the bases oriented with respect to the helix axis?

  • Parallel
  • At a 45-degree angle
  • At a 90-degree angle
  • Perpendicular (correct)
  • Which statement about the positioning of purine and pyrimidine bases is correct?

  • Inside the helix (correct)
  • In between the helix layers
  • Outside the helix
  • Adjacent to the phosphate units
  • How are the planes of sugars oriented in relation to the bases in the DNA helix?

    <p>Nearly at right angles to those bases</p> Signup and view all the answers

    How are adjacent bases separated along the helix according to the text?

    <p>34A</p> Signup and view all the answers

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

    <p>Hydrogen bonds between pairs of bases</p> Signup and view all the answers

    Which scientist conducted chemical analysis that provided important clues about DNA's structure?

    <p>Erwin Chargaff</p> Signup and view all the answers

    What type of pairing of bases is considered most important in the DNA double helix structure?

    <p>Specificity of pairing of bases</p> Signup and view all the answers

    Why did Watson and Crick deduce that adenine must pair with thymine and guanine with cytosine?

    <p>Due to steric and hydrogen-bonding features</p> Signup and view all the answers

    What important discovery did Erwin Chargaff's chemical analysis reveal about DNA?

    <p>Equal concentration of Adenine with Thymine and Guanine with Cytosine</p> Signup and view all the answers

    Study Notes

    Nucleic Acids

    • Nucleic acids are composed of pentose sugar, nitrogenous base, and phosphate molecules.
    • There are two types of nucleic acids: DNA (deoxynucleoside phosphate) and RNA (nucleoside phosphate).

    Nucleoside

    • A nucleoside is a combination of a nitrogenous base and a sugar molecule.
    • The sugar molecule is usually ribose or deoxyribose.
    • The base is linked to the sugar molecule at carbon 1, and the phosphate group is linked to the sugar molecule at carbon 5.

    Pentose Sugars

    • Pentose sugars are 5-carbon monosaccharide molecules.
    • There are two types of pentose sugars: ribose and deoxyribose.
    • Ribose is the pentose sugar found in RNA.
    • Deoxyribose is the pentose sugar found in DNA, and it lacks one oxygen atom at carbon 2.

    Nitrogenous Bases

    • Nitrogenous bases are heterocyclic amines that can accept a proton.
    • There are two types of nitrogenous bases: purine and pyrimidine.
    • Purine bases have a double-ringed structure and include adenine and guanine.
    • Pyrimidine bases have a 6-membered ring structure and include cytosine, thymine, and uracil.
    • Adenine and guanine are found in both DNA and RNA, while thymine is only found in DNA and uracil is only found in RNA.

    Phosphodiester Bond

    • A phosphodiester bond is a chemical bond formed between the hydroxyl group of one nucleotide and another nucleotide.
    • It is the bond between two nucleotides, with the 5' end of one nucleotide and the 3' end of another.

    Nomenclature

    • Nucleotides are named based on the nitrogenous base and the sugar molecule.
    • Examples of nucleotide names include deoxyadenosine monophosphate (dAMP), deoxyguanosine monophosphate (dGMP), and deoxythymidine monophosphate (dTMP).

    DNA Structure

    • The DNA double helix structure was discovered by James Watson and Francis Crick in 1953.
    • The structure consists of two helical polynucleotide chains coiled around a common axis.
    • The chains run in anti-parallel directions, and the phosphate and deoxyribose units are outside the helix.
    • The purine and pyrimidine bases are inside the helix, and the planes of the bases are perpendicular to the helix axis.
    • The diameter of the helix is 20A, and the adjacent bases are separated by 34A along the helix.
    • The helical structure repeats after 10 residues on each chain at intervals of 34A.
    • The two chains are held together by hydrogen bonds between pairs of bases.
    • Adenine pairs with thymine, and guanine pairs with cytosine.
    • Any sequence of bases may occur along a polynucleotide chain, and the precise sequence of bases carries genetic information.

    Chargaff's Rule

    • Chargaff's Rule, also known as the Fidelity Rule, states that the concentration of adenine is equal to that of thymine, and the concentration of guanine is equal to that of cytosine.
    • This rule was discovered by Erwin Chargaff in 1950 and provided important clues about the structure of DNA.

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    Description

    Test your knowledge on the basic monomer building blocks of nucleic acids, composed of a pentose sugar, nitrogenous base, and phosphate molecules. Learn about nucleosides, which are formed when a purine or pyrimidine base is linked to a sugar molecule, usually Ribose or Deoxyribose.

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