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

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

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

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

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  4. ==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==

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