1. Biology: Life on Earth Eighth Edition Biology: Life on Earth Eighth Edition Lecture for Chapter 9 Molecules of Heredity Lecture for Chapter 9 Molecules of Heredity Copyright © 2008 Pearson Prentice Hall, Inc. Teresa Audesirk Gerald Audesirk Bruce E. Byers

3. Chapter 9 Outline 9.1 How Did Scientists Discover That Genes Are Made of DNA? p. 150 9.2 What Is the Structure of DNA? p. 151 9.3 How Does DNA Encode Information? p. 157 9.4 How Does DNA Replication Ensure Genetic Constancy During Cell Division? p. 157 9.5 How Do Mutations Occur? p. 158

4. Section 9.1 Outline 9.1 How Did Scientists Discover That Genes Are Made of DNA? –Transformed Bacteria Revealed the Link Between Genes and DNA

5. Genes Are Made of DNA Known since the late 1800s: 1.Heritable information is carried in discrete units called genes 2.Genes are parts of structures called chromosomes 3.Chromosomes are made of deoxyribonucleic acid (DNA) and protein

6. Genes Are Made of DNA Transformed bacteria revealed the link between genes and DNA

7. Genes Are Made of DNA F. Griffith worked with two strains of Streptococcus pneumoniae bacteria –S strain caused pneumonia when injected into mice, killing them –R strain did not cause pneumonia when injected

8. Genes Are Made of DNA Griffith made a sample of heat-killed S strain and mixed it with R strain –Injection of combination into mice caused pneumonia and death

9. Genes Are Made of DNA Deductions from Griffith’s experiment (1920s) –Living safe bacteria (R strain) were changed by something in the dead (but normally disease- causing) S strain –The living R strain bacteria were transformed by genetic material released by the S strain

14. Genes Are Made of DNA Later findings by Avery, MacLeod, and McCarty (1940s) –The transforming molecule from the S strain was DNA

17. Section 9.2 Outline 9.2 What Is the Structure of DNA? –DNA Is Composed of Four Nucleotides –DNA Is a Double Helix of Two Nucleotide Strands –Hydrogen Bonds Between Complementary Bases Hold Two DNA Strands Together

18. DNA Is Composed of Four Nucleotides DNA is made of chains of small subunits called nucleotides

21. DNA Is Composed of Four Nucleotides Each nucleotide has three components: 1.Phosphate group 2.Deoxyribose sugar 3.One of four nitrogen-containing bases –Thymine –Cytosine –Adenine –Guanine

22. DNA Is Composed of Four Nucleotides In 1940, biochemist E. Chargaff determined that: –In a DNA molecule, amounts of A = T, G = C –“Chargaff’s Rule”

23. DNA Is a Double Helix In the 1940s several other scientists investigated the structure of DNA

24. DNA Is a Double Helix Rosalind Franklin and Maurice Wilkins studied DNA structure using X-ray scattering

26. DNA Is a Double Helix From X-ray diffraction patterns they deduced that DNA –Is long and thin –Has a uniform diameter of 2 nanometers –Is helical, and is twisted like a corkscrew –Consists of repeating subunits

27. DNA Is a Double Helix James Watson and Francis Crick combined the X-ray data with bonding theory to deduce DNA structure: –DNA is made of two strands of nucleotides –The deoxyribose and phosphate portions make up the sugar-phosphate backbone

29. Hydrogen Bonds Nitrogen-containing bases protrude inward from sugar-phosphate backbone

30. Hydrogen Bonds Hydrogen bonds hold certain nitrogenous base pairs together –A bonds with T, G bonds with C –Bonding bases called complementary base pairs

31. Hydrogen Bonds Ladder-like structure of the two DNA strands are twisted into a double helix

33. Section 9.3 Outline 9.3 How Does DNA Encode Information?

34. How Does DNA Encode Information? How can a molecule with only 4 simple parts be the carrier of genetic information? The key lies in the sequence, not number, of subunits

35. How Does DNA Encode Information? Within a DNA strand, the four types of bases can be arranged in any linear order, and this sequence is what encodes genetic information

36. How Does DNA Encode Information? The genetic code is analogous to languages, where small sets of letters combine in various ways to make up many different words – English has 26 letters – Hawaiian has 2 letters – The binary language of computers uses only two “letters” (0 and 1, or “on” and “off”)

37. How Does DNA Encode Information? The sequence of only four nucleotides can produce many different combinations –A 10 nucleotide sequence can code for greater than 1 million different combinations

38. Section 9.4 Outline 9.4 How Does DNA Replication Ensure Genetic Constancy During Cell Division? –Replication of DNA Is a Critical Event in a Cell’s Life –Replicated DNA Is Half New and Half Old

39. DNA Replication All cells come from pre-existing cells Cells reproduce by dividing in half

40. DNA Replication Each of two daughter cells gets an exact copy of parent cell’s genetic information Duplication of the parent cell DNA is called replication

41. DNA Replication DNA replication begins when DNA helicases separate the two strands –Hydrogen bonds between bases are broken

42. DNA Replication A second strand of new DNA is synthesized along each separated strand by DNA polymerases, which position free nucleotides across from complementary nucleotides

44. DNA Replication Base pairing is the foundation of DNA replication –An adenine on one strand pairs with a thymine on the other strand; a cytosine pairs with guanine –If one strand reads ATG, the other reads TAC

46. DNA Replication The two resulting DNA molecules have one old parental strand and one new strand (semiconservative replication)

48. Section 9.5 Outline 9.5 How Do Mutations Occur? –Accurate Replication and Proofreading Produce Almost Error-Free DNA –Mistakes Do Happen –Mutations Range from Changes in Single Nucleotides to Movements of Large Pieces of Chromosomes –Mutations May Have Varying Effects on Function

49. Replication And Proofreading During replication, DNA polymerase mismatches nucleotides once every 10,000 base pairs DNA repair enzymes “proofread” each new daughter strand, replacing mismatched nucleotides However…

50. Mistakes Do Happen DNA is damaged in a number of ways Spontaneous chemical breakdown at body temperature Certain chemicals (some components of cigarette smoke)

51. Mistakes Do Happen UV light from the sun causes DNA damage –DNA damage leads to uncontrollable cell division and skin cancer

52. Types of Mutations Point mutation - individual nucleotide in the DNA sequence is changed Insertion mutation - one or more nucleotide pairs are inserted into the DNA double helix Deletion mutation - one or more nucleotide pairs are removed from the double helix

53. Types of Mutations Inversion - piece of DNA is cut out of a chromosome, turned around, and re- inserted into the gap Translocation - chunk of DNA (often very large) is removed from one chromosome and attached to another