1. Overview: Life’s Operating Instructions DNA, the substance of heredity, is the most celebrated molecule of our time Hereditary information is encoded in DNA and reproduced in “all” cells of the body This DNA program directs the development of biochemical, anatomical, physiological, and (to some extent) behavioral traits

2. Concept 16.1: DNA is the genetic material Early in the 20th century, the identification of the molecules of inheritance loomed as a major challenge to biologists The discovery of the genetic role of DNA began with research by Griffith in 1928 Griffith showed that bacteria contained a substance that could cause a genetic transformation In 1944, Avery, McCarty and MacLeod announced that the transforming substance was DNA

3. More evidence for DNA as the genetic material came from studies of viruses that infect bacteria Such viruses, called bacteriophages (or phages), are widely used in molecular genetics research

4. Bacteriophages were widely accepted as a model system Consist of DNA and protein Known to re- program genetics of infected cell

5. Alfred Hershey-Martha Chase “Blender” Experiment

6. In 1953, James Watson and Francis Crick introduced an elegant double- helical model for the structure of deoxyribonuclei c acid, or DNA

7. Watson and Crick relied on other scientists’ data Rosalind Franklin produced some of the important X ray crystallographic images

8. 5 end Nucleoside Nitrogenous base Phosphate group Sugar (pentose) (b) Nucleotide Polynucleotide, or nucleic acid - a polymer made of nucleotide monomers Nucleotide = base + sugar + phosphate Nucleoside = base + sugar 3 end 3C3C 3C3C 5C5C 5C5C Nitrogenous bases Pyrimidines Cytosine (C) Thymine (T, in DNA)Uracil (U, in RNA) Purines Adenine (A)Guanine (G) Sugars Deoxyribose (in DNA) Ribose (in RNA) (c) Nucleoside components: sugars

9. The nucleotides are linked by phosphodiester bonds Sugar–phosphate backbone 5 end Nitrogenous bases Thymine (T) Adenine (A) Cytosine (C) Guanine (G) DNA nucleotide Sugar (deoxyribose) 3 end Phosphate

10. (c) Space-filling model 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 Watson and Crick’s key contribution was the base-pair

11. Cytosine (C) Adenine (A) Thymine (T) Guanine (G) Watson- Crick base pairs Other types can form- and they do!

12. Concept 16.2: Many proteins work together in DNA replication and repair The relationship between structure and function is obvious in the double helix Watson and Crick noted that the specific base pairing suggested a possible copying or replication mechanism for genetic material

13. 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

14. 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

15. Which Model? Conservative (top)? Semi-conservative (middle)? Dispersive (bottom)? Meselson-Stahl experiment

16. The place on a DNA molecule where replication begins is an origin of replication or ori Special sequence of DNA bases that signals the replication machinery to assemble Many enzymes are involved: DNA helicase, DNA topoisomerase, DNA ligase. The “growth point” is the replication fork

17. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings PowerPoint ® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp (a) Origin of replication in an E. coli cell (b) Origins of replication in a eukaryotic cell Origin of replication Parental (template) strand Double- stranded DNA molecule Daughter (new) strand Replication fork Replication bubble Two daughter DNA molecules Origin of replication Double-stranded DNA molecule Parental (template) strand Daughter (new) strand Bubble Replication fork Two daughter DNA molecules 0.5  m 0.25  m

18. DNA polymerase (Dpol) multiple types involved Unidirectional enzyme (5’ to 3’ synthesis) How to replicate both strands of the double helix at each replication fork? The replication machinery has to go back and forth at each fork to copy both strands: leading strand and lagging strand. Dpol enzymes not good at initiating-require help from RNA polymerase: primer

19. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings PowerPoint ® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Origin of replication Overview Leading strand Lagging strand Overall directions of replication 1 2 DNA polymerase works in only one direction.

20. Unidirectional enzyme has problems at the ends of a linear DNA template Special adaptations required Some systems have modifications to the ends of the linear DNA More common-a special enzyme for synthesis of DNA ends is used: telomerase A polymerase with a portable RNA template

21. Proofreading and Repair DNA polymerases check their work as they go along and correct mistakes in real time: proofreading Remaining mistakes are removed later by a separate system of enzymes: mismatch repair Two important ways to ensure the integrity of DNA information

22. Note Card-Explain these concepts Semi conservative replication Bi-directional replication Discontinuous replication