Nucleic Acids

• What is the structure of DNA?

  The structure of DNA is a double helix, consisting of two strands of nucleotides that are connected by hydrogen bonds between complementary bases.
• What are the base pairings of the four nucleotide bases in DNA?

  Adenine - Thymine

  Cytosine - Guanine
• What is a nucleotide made from?

  pentose sugar, phosphate, nitrogenous base
• What is the purpose of DNA?

  Carries genetic information and is a highly stable molecule.
• If DNA is a polymer, nucleotides are what?

  Monomers
• Adenine and Thymine have how many hydrogen bonds between them?

  Two
• Cytosine and Guanine have how many Hydrogen bonds between them?

  Three
• How are nucleotides joined together?

  Through phosphodiester bonds in a condensation reaction.
• What are the two properties of DNA?

  Degenerative and Universal
• What does it mean if DNA is degenerative?


  Some amino acids can be coded for by more than one codon.
• What does it mean in DNA is universal?

  All living organisms go by a specific set of rules to create proteins.
• What is a triplet code?

  Series of nucleotides that are non-overlapping.
• What is a codon?


  A codon is a sequence of three nucleotides in DNA or RNA that codes for a specific amino acid during protein synthesis.
• What are purines?


  Nitrogenous bases with 2 nitrogen containing rings and longer structures = Adenine and guanine.
• What are Pyrimidines?


  Nitrogenous bases with 1 nitrogen containing ring and shorter structures = Thymine and Cytosine
• How do purines and pyrimidines bind to ensure there is no mutation?

  Purine + Pyrimidine = normal

  Purine + Purine/ Pyrimidine + Pyrimidine = mutation
• What replication is DNA replication?

  Semi-conservative
• How does DNA replicate?

  DNA helicase breaks hydrogen bonds between DNA strands,

  DNA primase binds and forms a primer to the DNA strand,

  DNA polymerase binds to the primer and moves along the strand,

  Polymerase bonds complementary nucleotides from the 3prime end to the 5prime end to form a new strand,

  Forms phosphodiester bonds between adjacent nucleotides,

  Exonuclease then removes the primer and gaps are filled in,

  DNA ligase seals the strands together.
• What is the Meselson and Stahl experiment's purpose?

  Provides evidence for semi-conservative replication of the DNA molecule.
• What is the Meselson and Stahl experiment?

  Bacterial cells were grown for several generations on a medium containing a heavy isotope of nitrogen.

  The cells were then transferred to a new medium containing a lighter nitrogen isotope.

  Bacteria were collected at various times and the DNA was extracted.

  The DNA was dissolved in caesium chloride and spun rapidly in a centrifuge.
• Why, in the Meselson and Stahl Experiment, is caesium chloride used?

  When centrifuged, caesium establishes a density gradient within the tube. DNA molecules move in the gradient until they meet a place where their density equals that of Caesium.
• What did the results of the Meselson and Stahl experiment show?

  Semi-conservative DNA replication occurs.

  The F1 Generation shows only N14 - N15 DNA, and the F2 generation shows some only N14 and N14-N15 DNA which would have occurred when the N14 - N15 strand split and the N14 was used as a template.
• What is the structure of RNA?

  RNA is a single-stranded molecule composed of nucleotides, which consist of a sugar, a phosphate group, and a nitrogenous base (adenine, guanine, cytosine, or uracil).