Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. CHAPTER 14 LECTURE SLIDES To run the animations you must be in Slideshow View. Use the buttons on the animation to play, pause, and turn audio/text on or off. Please note: once you have used any of the animation functions (such as Play or Pause), you must first click in the white background before you advance the next slide.

DNA: The Genetic Material Chapter 14

Frederick Griffith – 1928 Studied Streptococcus pneumoniae, a pathogenic bacterium causing pneumonia 2 strains of Streptococcus –S strain is virulent –R strain is nonvirulent Griffith infected mice with these strains hoping to understand the difference between the strains 3

4 Griffith’s results –Live S strain cells killed the mice –Live R strain cells did not kill the mice –Heat-killed S strain cells did not kill the mice –Heat-killed S strain + live R strain cells killed the mice

5

6

7 Transformation –Information specifying virulence passed from the dead S strain cells into the live R strain cells Our modern interpretation is that genetic material was actually transferred between the cells

8 Avery, MacLeod, & McCarty – 1944 Repeated Griffith’s experiment using purified cell extracts Removal of all protein from the transforming material did not destroy its ability to transform R strain cells DNA-digesting enzymes destroyed all transforming ability Supported DNA as the genetic material

9 Hershey & Chase –1952 Investigated bacteriophages –Viruses that infect bacteria Bacteriophage was composed of only DNA and protein Wanted to determine which of these molecules is the genetic material that is injected into the bacteria

10 Bacteriophage DNA was labeled with radioactive phosphorus ( 32 P) Bacteriophage protein was labeled with radioactive sulfur ( 35 S) Radioactive molecules were tracked Only the bacteriophage DNA (as indicated by the 32 P) entered the bacteria and was used to produce more bacteriophage Conclusion: DNA is the genetic material

11

12 Rosalind Franklin Performed X-ray diffraction studies to identify the 3-D structure –Using Maurice Wilkins’ DNA fibers, discovered that DNA is helical

13 James Watson and Francis Crick – 1953 Deduced the structure of DNA using evidence from Chargaff, Franklin, and others Did not perform a single experiment themselves related to DNA Proposed a double helix structure

14 DNA Structure DNA is a nucleic acid Composed of nucleotides –5-carbon sugar called deoxyribose –Phosphate group (PO 4 ) –Nitrogenous base Adenine, thymine, cytosine, guanine

Chargaff’s Rules Erwin Chargaff determined that –Amount of adenine = amount of thymine –Amount of cytosine = amount of guanine –Always an equal proportion of purines (A and G) and pyrimidines (C and T) 15

Complementarity bases A forms 2 hydrogen bonds with T G forms 3 hydrogen bonds with C 16 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A H Sugar T G C N H N O H CH 3 H H N N N H N N N H H H N O H H H N NH N N H N N Hydrogen bond Hydrogen bond

17 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Purines Pyrimidines Adenine Guanine NH 2 C C N N N C H N C CH O H H OC NC H N C H C H O O C N C H N C H3CH3C C H H O O C N C H N C H C H C C N N N C H N C CH H Nitrogenous Base 4´4´ 5´5´ 1´1´ 3´3´2´2´ O P O–O– –O–O Phosphate group Sugar Nitrogenous base O CH 2 N N O N NH 2 OH in RNA Cytosine (both DNA and RNA) Thymine (DNA only) Uracil (RNA only) OH H in DNA

Double helix 2 strands are polymers of nucleotides Backbone – repeating sugar and phosphate units joined by phosphodiester bonds Antiparallel - Each DNA molecule consists of two parallel strands of nucleotides running in opposite directions The chain of nucleotides has a 5′-to-3′ orientation 18 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 5´5´ 3´3´ P P P P OH 5-carbon sugar Nitrogenous base Phosphate group Phosphodiester bond O O O O 4´4´ 5´5´ 1´1´ 3´3´ 2´2´ 4´4´ 5´5´ 1´1´ 3´3´ 2´2´ 4´4´ 5´5´ 1´1´ 3´3´ 2´2´ 4´4´ 5´5´ 1´1´ 3´3´ 2´2´

19

20 DNA Replication Requires 3 things –Something to copy Parental DNA molecule –Something to do the copying Enzymes –Building blocks to make copy Nucleotide triphosphates

21 DNA replication includes –Initiation – replication begins –Elongation – new strands of DNA are synthesized by DNA polymerase –Termination – replication is terminated

DNA REPLICATION: 1. Introduction: DNA holds the genetic code which is passed from parents to their offspring. During interphase of the cell cycle, our DNA is replicated or duplicated so each new daughter cell is provided with an identical copy of this genetic material. 2. PROCESS OF DNA REPLICATION: a. DNA uncoils, and unzips (hydrogen bonds are broken between A:T and G:C); · Each free nucleotide strand now serves as a template (a set of instructions) for building a new complementary DNA strand.

b. DNA nucleotides that are present in the nucleoplasm begin to match up with their complements on the templates. c.This results in two identical DNA molecules, each consisting of one old and one newly assembled nucleotide strand.  This type of replication is called semi-conservative replication.

25

DNA polymerase –Matches existing DNA bases with complementary nucleotides and links them –All have several common features Add new bases to 3′ end of existing strands Synthesize in 5′-to-3′ direction Require a primer of RNA 26 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 5´5´ 3´3´ 5´5´ 5´5´ 5´5´ 3´3´ 3´3´ RNA polymerase makes primerDNA polymerase extends primer

Helicases – use energy from ATP to unwind DNA DNA polymerase can synthesize only in 1 direction Leading strand synthesized continuously from an initial primer Lagging strand synthesized discontinuously with multiple priming events –Okazaki fragments 27

28

29 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 5´ 3´ Primase RNA primer Okazaki fragment made by DNA polymerase III Leading strand (continuous) DNA polymerase I Lagging strand (discontinuous) DNA ligase

30 Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at

Telomeres Specialized structures found on the ends of eukaryotic chromosomes Protect ends of chromosomes from nucleases and maintain the integrity of linear chromosomes Gradual shortening of chromosomes with each round of cell division 31

32

33 DNA Repair Errors due to replication –DNA polymerases have proofreading ability Mutagens – any agent that increases the number of mutations above background level –Radiation and chemicals

34 DNA Repair 1.Specific repair –Targets a single kind of lesion in DNA and repairs only that damage 2.Nonspecific –Use a single mechanism to repair multiple kinds of lesions in DNA

35 Ex. Photorepair Specific repair mechanism For one particular form of damage caused by UV light

36

Excision repair Nonspecific repair Damaged region is removed and replaced by DNA synthesis 3 steps 1.Recognition of damage 2.Removal of the damaged region 3.Resynthesis using the information on the undamaged strand as a template 37

38