Genetics DNA II: The structure of DNA by Nathan H Lents, Ph.D. Reading Quiz Teach with this 1. What are the building blocks of DNA? amino acids proteins helices nucleotides 2. What are the three "parts" of a nucleotide? nuclein, helix, and amino acid protein, DNA, sugar sugar, phosphate, nitrogen base adenine, thymine, cytosine 3. Whose work showed that all living things have different amounts of each of the four nucleotides, and disproved Phoebus Leven’s hypothesis of the “tetranucleotide” structure of DNA? Erwin Chargaff J. Friedrich Miescher Rosalind Franklin James Watson 4. Why was Rosalind Franklin's famous X-ray diffraction picture of DNA so important? It showed that DNA has a triple helix. It helped to reveal the molecular structure of DNA. It proved that Watson and Crick's original model was correct. It showed that there are more than four nucleotides that make up DNA. 5. What forms the "bridge" connecting two nucleotides within a single strand of the DNA polymer? phosphate electrons cytosine hydrogen bond 6. DNA is typically double stranded. Which of the following statements about the two strands of DNA is NOT correct? The two strands are oriented in opposite directions (anti-parallel) The two strands are held together by hydrogen bonds. The phosphate groups are pointed "inwards" toward the center of the molecule. The two strands twist around each other. 7. When they announced their proposed structure of DNA, Watson and Crick noted that, “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.” What did they mean by this? The twisting nature of the molecule would make it very easy to copy. Because A always base-pairs with T, phosphates would always bond with the sugars. Hydrogen bonding is much weaker than covalent bonding, so the molecule could be easily taken apart and re-built when necessary. If the two strands of DNA were separated, both separate strands could be used as templates for copying the other strand, according to the complementary base pairing. Score Quiz
