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lecture 12

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Terms in this set (20)

  • What are the three main components of a nucleotide?

    Heterocyclic nitrogenous base, sugar (ribose or deoxyribose), and phosphate group.

  • Difference between a nucleoside and a nucleotide?

    A nucleoside consists of a sugar and a nitrogenous base, while a nucleotide also includes one or more phosphate groups.

  • What are the two types of nitrogenous bases in nucleotides?

    Purines (adenine, guanine) and pyrimidines (cytosine, thymine in DNA, uracil in RNA).

  • What sugar is found in DNA and how does it differ from RNA sugar?

    DNA contains deoxyribose, which lacks an oxygen atom at the 2' carbon compared to ribose in RNA.

  • How are nucleotides linked to form nucleic acids?

    By phosphodiester bonds between the 3' hydroxyl of one sugar and the 5' phosphate of the next, forming a sugar-phosphate backbone.

  • What is the directionality convention for writing nucleic acid sequences?

    Sequences are written from the 5' end to the 3' end, reflecting the orientation of the sugar-phosphate backbone.

  • What are the key differences between DNA and RNA?

    DNA has deoxyribose, uses thymine (T), and is usually double-stranded. RNA has ribose, uses uracil (U), and is usually single-stranded.

  • What stabilizes the double helix structure of DNA?

    Hydrogen bonding between complementary bases and dispersion (stacking) forces between aromatic bases stabilize the helix.

  • How many hydrogen bonds form between A-T and G-C base pairs?

    A-T pairs form 2 hydrogen bonds, while G-C pairs form 3 hydrogen bonds, making G-C pairs more stable.

  • What is the antiparallel nature of DNA strands?

    Two DNA strands run in opposite directions: one strand runs 5' to 3', the other 3' to 5'.

  • What is Chargaff's rule regarding base composition in DNA?

    In double-stranded DNA, the amount of adenine equals thymine, and the amount of guanine equals cytosine.

  • What is the reverse complement of a DNA sequence?

    The sequence formed by taking the complement of each base (A-T, C-G) and reversing the strand direction (3' to 5' becomes 5' to 3').

  • What is the function of histone proteins in DNA packaging?

    Histones are positively charged proteins that DNA wraps around to form nucleosomes, compacting DNA into chromatin.

  • Which amino acids are abundant in histones and why?

    Arginine (Arg) and lysine (Lys) are abundant because their positive charges interact electrostatically with negatively charged DNA phosphates.

  • What is the central dogma of molecular biology?

    Information flows from DNA to RNA to protein via replication, transcription, and translation.

  • What is semiconservative DNA replication?

    Each new DNA double helix contains one original (parental) strand and one newly synthesized strand.

  • How can mutations arise in DNA?

    Mutations can be caused by mutagens like UV radiation or chemical agents, leading to base changes that may be propagated during replication.

  • Why is uracil not normally found in DNA?

    Because cytosine can spontaneously deaminate to uracil, DNA repair enzymes recognize uracil as a mutation and remove it to maintain fidelity.

  • What is the role of hydrogen bond donors and acceptors in base pairing?

    Specific patterns of hydrogen bond donors and acceptors on bases enable complementary base pairing and DNA double helix stability.

  • How do proteins recognize specific DNA sequences?

    Proteins read unique patterns of hydrogen bond donors and acceptors in the major groove of DNA to bind sequence-specifically.