1. Section II The Structure of DNA

2. How can a DNA molecule be compared to a ladder used in everyday life? Similarities? Differences? vs Figure 4, pg. 194

3. James Watson and Francis Crick pieced together a model that represents the structure of DNA Why is it important for these scientists to discover the structure of DNA? It clarified how DNA could serve as the genetic material

4. The structure of DNA is considered to be a double helix Double helix: two strands twisted around each other, like a “winding staircase”

5. The two strands within the double helix are made of linked nucleotides Nucleotides: subunits that make up DNA Nucleotide = phosphate group + 5 carbon sugar molecule + nitrogen-containing base 5 carbon sugar molecule: also known as deoxyribose, from which DNA gets its full name DeoxyriboNucleic Acid Phosphate group and the 5 carbon sugar molecule are the same for each nucleotide Nitrogen-containing base differs for each nucleotide

6. A nitrogen-containing base can be one of four: Adenine (A) Guanine (G) Thymine (T) Cytosine (C) Adenine and Guanine are considered to be purines Purines: nitrogen bases made of two rings of carbon and nitrogen atoms Thymine and Cyotsine are considered to be pyrimidines Pyrimidines: nitrogen bases made of a single ring of carbon and nitrogen atoms

7. Figure 5, pg. 195

8. Nitrogen bases pair together in a unique fashion, or in a complementary fashion How would you define complementary? Complementary base pairing refers to the fact that purines must always be paired with pyrimidines Purines and pyrimidines are never paired with themselves Why do you think that is? DNA molecule remains at a consistent width

9. Complementary base pairing: A - T (purine with pyrimidine) G - C (purine with pyrimidine) Can A pair with C? Can G pair with T? It is still a purine paired with a pyrimidine, right? NO, A paired with C and G paired with T is not accurate. A is structurally attracted to T and G is structurally attracted to C What holds A – T and G – C together? Hydrogen Bonds, allowing the double helix structure to be formed Example: Strand #1 will determine what strand #2 will be, due to complementary base pairing Strand #1: TCGAACT Strand #2: AGCTTGA

10. Figure 8, pg. 197

11. What does RNA stand for? RiboNucleic Acid RNA follows the same rules as we discussed for DNA, with a few exceptions Instead of just a sugar as in DNA nucleotide, a ribose sugar is incorporated into the structure of a RNA nucleotide Instead of the pyrimidine thymine (T) as in DNA, the pyrimidine uracil (U) is used in RNA. A = U Instead of being double stranded as in DNA, there is a single strand representing RNA

13. The discovery of DNA’s structure was made possible by a variety of contributions Chargaff’s Contribution Determined that the number of A’s equals the number of T’s, and that the number of G’s equals the number of C’s The amount of paired AT and GC differs from organism to organism Wilkins and Franklin’s Contribution Developed high-quality x-ray diffraction photographs of strands of DNA, exposing a coiled helix structure made of nucleotide chains Watson and Crick’s Contribution Built a 3D model of DNA, showcasing the double helix structure

14. Sugar phosphate backbones = side rails of a ladder Paired nitrogen bases = rungs of the ladder EXIT SLIP: Describe another item that is used in everyday life, relating it to the structure of DNA (i.e. ladder) vs