1. Fig. 16-8 Cytosine (C) Adenine (A)Thymine (T) Guanine (G)

2. Fig. 16-UN2 Sugar-phosphate backbone Nitrogenous bases Hydrogen bond G C A T G G G A A A T T T C C C

3. Fig. 16-7a Hydrogen bond 3 end 5 end 3.4 nm 0.34 nm 3 end 5 end (b) Partial chemical structure(a) Key features of DNA structure 1 nm

4. Fig. 16-5 Sugar–phosphate backbone 5 end Nitrogenous bases Thymine (T) Adenine (A) Cytosine (C) Guanine (G) DNA nucleotide Sugar (deoxyribose) 3 end Phosphate Purines Adenine Guanine PurAsGold Pyrimidines Cytosine Thymine Uracil PyCUT Carbon 1 – bonds to nitrogen base Carbon 3 – bonds to next nucleotide Carbon 5 – bonds to phosphate group

5. Fig. 16-UN1 Purine + purine: too wide Pyrimidine + pyrimidine: too narrow Purine + pyrimidine: width consistent with X-ray data

6. At first, Watson and Crick thought the bases paired like with like (A with A, and so on), but such pairings did not result in a uniform width Instead, pairing a purine with a pyrimidine resulted in a uniform width consistent with the X-ray Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

7. Watson and Crick reasoned that the pairing was more specific, dictated by the base structures They determined that adenine (A) paired only with thymine (T), and guanine (G) paired only with cytosine (C) The Watson-Crick model explains Chargaff’s rules: in any organism the amount of A = T, and the amount of G = C Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

8. Concept 16.2: Many proteins work together in DNA replication and repair The relationship between structure and function is manifest in the double helix Watson and Crick noted that the specific base pairing suggested a possible copying mechanism for genetic material Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings

9. Fig. 16-9-1 A T G C TA TA G C (a) Parent molecule

10. Fig. 16-9-2 A T G C TA TA G C A T G C T A T A G C (a) Parent molecule (b) Separation of strands

11. Fig. 16-9-3 A T G C TA TA G C (a) Parent molecule AT GC T A T A GC (c) “Daughter” DNA molecules, each consisting of one parental strand and one new strand (b) Separation of strands A T G C TA TA G C A T G C T A T A G C

12. The Basic Principle: Base Pairing to a Template Strand Since the two strands of DNA are complementary, each strand acts as a template for building a new strand in replication In DNA replication, the parent molecule unwinds, and two new daughter strands are built based on base-pairing rules Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Animation: DNA Replication Overview Animation: DNA Replication Overview

13. Fig. 17-5 Second mRNA base First mRNA base (5 end of codon) Third mRNA base (3 end of codon)

14. Enzymes involved in DNA Replication & Transcription EnzymeFunction Helicase“molecular zipper” – unwinds double helix; breaks hydrogen bonds that holds base pairs together Topoisomerase (gyrase)“molecular swivel”- relieves overwinding stress on DNA strands by working ahead of helicase and breaking, swiveling and rejoining small sections of the DNA molecule DNA polymeraseUsing a parent DNA strand, adds free- floating nucleotides (A, T, G, & C’s) covalently to the new strand being constructed. ligase“molecular glue” – joins fragments of the New DNA strand together RNA polymerase (used in transcription)Uses one strand of DNA as a template to construct mRNA – adds free-floating nucleotide EditaseFixes mistakes on DNA molecule

16. Transcription & Translation refer to diagram drawn on board also watch animations: DNAi.org Khanacademy.org Crash Course (youtube)