CN

DNA Structure and Replication Quiz 

DNA Structure

DNA = Deoxyribonucleic Acid - Nucleotide

  • Comprised of ==3 parts - 5-carbon sugar (deoxyribose), phosphate, nitrogenous base==
  • 2 Types Nitrogenous Bases: Purines (2 rings) and Pyrimidines (1 ring)
    • Purines: Adenine, Guanine
    • Pyrimidines: Cytosine, Thymine
    • Adenine pairs with Thymine (A&T)
    • Guanine pairs with Cytosine (G&C)
    • ==Bases held together by hydrogen bonds==
  • Percentage of Bases in DNA
    • percentage of A (Adenine) = percentage of T (Thymine)
    • Shape of DNA - Double Helix
    • 2 antiparallel strands - phosphate-sugar backbone
    • ==Phosphate and sugar held by covalent bonds==
    • percentage of C (Cytosine) = percentage of G (Guanine)

DNA Replication

Steps of DNA Replication

  • \

    1. Nucleotide chains separated at the replication fork by enzyme ==Helicase== - breaks hydrogen bonds between bases

  • \

    1. ==SSBP (Single-Strand Binding Proteins)== attach to the separate strands, prevent them from coming back together

  • \

    1. ==Primase== makes RNA primer to signal starting point to DNA Polymerase

  • \

    1. ==DNA Polymerase III== binds to primer, adding nucleotides to the 3’ of the separated strands
    • Synthesis is always bidirectional - ==always made in the 5’-3’ direction==

  • Leading Strand

    • Continuous strand that is made in the direction of the replication fork

  • Lagging Strand

    • Discontinuous strand made in the opposite direction of the replication fork
    • ==Okazaki Fragments==: sections of DNA about 100-200 base pairs long on the lagging strand
    • ==Ligase== ‘glues’ all the okazaki fragments together
    • ==Topoisomerase== cuts and rejoins the DNA downstream of the replication fork

  • Semi-Conservative Replication

    • When replication is finished, you get the ==original strand and a newly made daughter strand==