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PowerPoint Presentation Materials to accompany Genetics: Analysis and Principles Robert J. Brooker Copyright ©The McGraw-Hill Companies, Inc. Permission.

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Presentation on theme: "PowerPoint Presentation Materials to accompany Genetics: Analysis and Principles Robert J. Brooker Copyright ©The McGraw-Hill Companies, Inc. Permission."— Presentation transcript:

1 PowerPoint Presentation Materials to accompany Genetics: Analysis and Principles Robert J. Brooker Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display CHAPTER 9 MOLECULAR STRUCTURE OF DNA AND RNA

2 To fulfill its role, the genetic material must meet several criteria 1. Information: It must contain the information necessary to make an entire organism 2. Transmission: It must be passed from parent to offspring 3. Replication: It must be copied In order to be passed from parent to offspring 4. Variation: It must be capable of changes To account for the known phenotypic variation in each species 9-3 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 9.1 IDENTIFICATION OF DNA AS THE GENETIC MATERIAL

3 The data of many geneticists, including Mendel, were consistent with these four properties However, the chemical nature of the genetic material cannot be identified solely by genetic crosses 9-4 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 9.1 IDENTIFICATION OF DNA AS THE GENETIC MATERIAL

4 Griffith studied a bacterium (Diplococcus pneumoniae) now known as Streptococcus pneumoniae S. pneumoniae comes in two strains S  Smooth Secrete a polysaccharide capsule Protects bacterium from the immune system of animals Produce smooth colonies on solid media R  Rough Unable to secrete a capsule Produce colonies with a rough appearance 9-5 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Frederick Griffith Experiments with Streptococcus pneumoniae

5 In addition, the capsules of two smooth strains can differ significantly in their chemical composition 9-6 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Figure 9.1 Rare mutations can convert a smooth strain into a rough strain, and vice versa However, mutations do not change the type of the strain

6 9-7 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display In 1928, Griffith conducted experiments using two strains of S. pneumoniae: type IIIS and type IIR 1. Inject mouse with live type IIIS bacteria Mouse died Type IIIS bacteria recovered from the mouse’s blood 2. Inject mouse with live type IIR bacteria Mouse survived No living bacteria isolated from the mouse’s blood 3. Inject mouse with heat-killed type IIIS bacteria Mouse survived No living bacteria isolated from the mouse’s blood 4. Inject mouse with live type IIR + heat-killed type IIIS cells Mouse died Type IIIS bacteria recovered from the mouse’s blood

7 9-8 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Figure 9.2

8 9-9 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Griffith concluded that something from the dead type IIIS was transforming type IIR into type IIIS He called this process transformation The substance that allowed this to happen was termed the transformation principle Griffith did not know what it was The nature of the transforming principle was determined using experimental approaches that incorporated various biochemical techniques

9 Avery, MacLeod and McCarty realized that Griffith’s observations could be used to identify the genetic material They carried out their experiments in the 1940s At that time, it was known that DNA, RNA, proteins and carbohydrates are major constituents of living cells They prepared cell extracts from type IIIS cells containing each of these macromolecules Only the extract that contained purified DNA was able to convert type IIR into type IIIS Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display The Experiments of Avery, MacLeod and McCarty 9-10

10 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 9-11 Figure 9.3 Avery et al also conducted the following experiments To further verify that DNA, and not a contaminant (RNA or protein), is the genetic material

11 In 1952, Alfred Hershey and Marsha Chase provided further evidence that DNA is the genetic material Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Hershey and Chase Experiment with Bacteriophage T They studied the bacteriophage T2 It is relatively simple since its composed of only two macromolecules DNA and protein Figure 9.4 Made up of protein Inside the capsid

12 Figure 9.5 Life cycle of the T2 bacteriophage

13 The Hershey and Chase experiment can be summarized as such: Used radioisotopes to distinguish DNA from proteins 32 P labels DNA specifically 35 S labels protein specifically Radioactively-labeled phages were used to infect nonradioactive Escherichia coli cells After allowing sufficient time for infection to proceed, the residual phage particles were sheared off the cells => Phage ghosts and E. coli cells were separated Radioactivity was monitored using a scintillation counter Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 9-14

14 The Hypothesis Only the genetic material of the phage is injected into the bacterium Isotope labeling will reveal if it is DNA or protein 9-15 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Testing the Hypothesis Refer to Figure 9.6

15 9-16 Figure 9.6 Testing the Hypothesis

16 9-17 Figure 9.6

17 The Data 9-18 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

18 Interpreting the Data 9-19 Most of the 35 S was found in the supernatant But only a small percentage of 32 P These results suggest that DNA is injected into the bacterial cytoplasm during infection This is the expected result if DNA is the genetic material

19

20 9-20 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display In 1956, A. Gierer and G. Schramm isolated RNA from the tobacco mosaic virus (TMV), a plant virus Purified RNA caused the same lesions as intact TMV viruses Therefore, the viral genome is composed of RNA Since that time, many RNA viruses have been found Refer to Table 9.1 RNA Functions as the Genetic Material in Some Viruses

21

22 9-21 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

23 DNA and RNA are large macromolecules with several levels of complexity 1. Nucleotides form the repeating units 2. Nucleotides are linked to form a strand 3. Two strands can interact to form a double helix 4. The double helix folds, bends and interacts with proteins resulting in 3-D structures in the form of chromosomes Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 9.2 NUCLEIC ACID STRUCTURE 9-22

24 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 9-23 Three-dimensional structure Figure 9.7

25 9-24 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display The nucleotide is the repeating structural unit of DNA and RNA It has three components A phosphate group A pentose sugar A nitrogenous base Refer to Figure 9.8 Nucleotides

26 9-25 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Figure 9.8

27 9-26 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Figure 9.9 The structure of nucleotides found in (a) DNA and (b) RNA A, G, C or T These atoms are found within individual nucleotides However, they are removed when nucleotides join together to make strands of DNA or RNA A, G, C or U

28 9-27 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Base + sugar  nucleoside Example Adenine + ribose = Adenosine Adenine + deoxyribose = Deoxyadenosine Base + sugar + phosphate(s)  nucleotide Example Adenosine monophosphate (AMP) Adenosine diphosphate (ADP) Adenosine triphosphate (ATP) Refer to Figure 9.10

29 9-28 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Figure 9.10 Base always attached here Phosphates are attached there

30 9-29 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Nucleotides are covalently linked together by phosphodiester bonds A phosphate connects the 5’ carbon of one nucleotide to the 3’ carbon of another Therefore the strand has directionality 5’ to 3’ The phosphates and sugar molecules form the backbone of the nucleic acid strand The bases project from the backbone

31 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. O–O– HH HO H H O O O P CH 2 Base Repeating unit of deoxyribonucleic acid (DNA) Repeating unit of ribonucleic acid (RNA) Phosphate 2 Deoxyribose O – HH OH HH O O O P CH 2 Base Phosphate Ribose O Fig. 9.9 (TE Art)

32 9-30 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Figure 9.11

33 Figure Copyright © 2006 Pearson Prentice Hall, Inc.

34 9-31 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display In 1953, James Watson and Francis Crick discovered the double helical structure of DNA The scientific framework for their breakthrough was provided by other scientists including Linus Pauling Rosalind Franklin and Maurice Wilkins Erwin Chargaff A Few Key Events Led to the Discovery of the Structure of DNA

35 9-32 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display In the early 1950s, he proposed that regions of protein can fold into a secondary structure  -helix Figure 9.12 To elucidate this structure, he built ball-and-stick models Refer to Figure 9.12b Linus Pauling

36 Fig Rosalind Franklin

37 Photo 51 x-ray diffraction of wet DNA showing the B form double helix taken by Rosalind Franklin and Raymond Gosling on Friday, 2nd May, 1952 by long exposure started the previous day

38 9-34 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display She made marked advances in X-ray diffraction techniques with DNA The diffraction pattern she obtained suggested several structural features of DNA Helical More than one strand 10 base pairs per complete turn Rosalind Franklin

39 9-35 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Chargaff pioneered many of the biochemical techniques for the isolation, purification and measurement of nucleic acids from living cells It was already known then that DNA contained the four bases: A, G, C and T Erwin Chargaff’s Experiment

40 The Hypothesis An analysis of the base composition of DNA in different species may reveal important features about the structure of DNA 9-36 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Testing the Hypothesis Refer to Figure 9.14

41 9-37 Figure 9.14

42 9-38 Figure 9.14

43 The Data 9-39 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

44 Table 10-3 Copyright © 2006 Pearson Prentice Hall, Inc.

45 Interpreting the Data 9-40 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display The compelling observation was that Percent of adenine = percent of thymine Percent of cytosine = percent of guanine the percentage of C + G does not necessarily equal the percentage of A + T This observation became known as Chargaff’s rule It was crucial evidence that Watson and Crick used to elucidate the structure of DNA

46 9-41 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Familiar with all of these key observations, Watson and Crick set out to solve the structure of DNA They tried to build ball-and-stick models that incorporated all known experimental observations A critical question was how the two (or more strands) would interact An early hypothesis proposed that the strands interact through phosphate-Mg ++ crosslinks Refer to Figure 9.15 Watson and Crick

47 9-42 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Figure 9.15 This hypothesis was, of course, incorrect!

48 9-43 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display They went back to the ball-and-stick units They then built models with the Sugar-phosphate backbone on the outside Bases projecting toward each other They first considered a structure in which bases form H bonds with identical bases in the opposite strand ie., A to A, T to T, C to C, and G to G Model building revealed that this also was incorrect Watson and Crick

49 9-44 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display They then realized that the hydrogen bonding of A and T resembled that between C and G So they built ball-and-stick models with AT and CG interactions These were consistent with all known data about DNA structure Refer to Figure 9.16 Watson, Crick and Maurice Wilkins were awarded the Nobel Prize in 1962 Rosalind Franklin died in 1958, and Nobel prizes are not awarded posthumously Watson and Crick

50 Fig. 9.16

51 9-45 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display General structural features (Figures 9.17 & 9.18) The DNA Double Helix Two strands are twisted together around a common axis There are 10 bases per complete twist The two strands are antiparallel One runs in the 5’ to 3’ direction and the other 3’ to 5’ The helix is right-handed As it spirals away from you, the helix turns in a clockwise direction

52 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. NH 2 T Key Features Two strands of DNA form a right-handed double helix. The bases in opposite strands hydrogen bond according to the AT/GC rule. The 2 strands are antiparallel with regard to their 5to 3 directionality. 2 nm One nucleotide 0.34 nm One complete turn 3.4 nm O O HH N N H H H H O OO O P O–O– NH 2 H N N N H N HH H OH HH O OO O–O– P O–O– H H H H H O OO O P O–O– NH 2 O O HH N N H2NH2N H N N N H N H H H HH O O O O–O– P O H H H H H O O O O–O– P O H N N H N N H H H H H O OO O–O– P O–O– H2NH2N HO 5  end3  end 3  hydroxyl 3  end5 end 5phosphate TA TA TA P P P P P S S S S S S S S A CG G CG CG G G C C GC G C GC C P P S P P P P P S S S S S P P P P P P P P S S S S S S S S S P S S P P P S S S S P CH 2 H2NH2N A P S P P H CH 3 H N N H O O There are ~10.0 nucleotides in each strand per complete 360° turn of the helix. Fig (TE Art)

53 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Space-filling model of DNA Ball-and-stick model of DNA Minor groove Major groove Minor groove Major groove Fig (TE Art)

54 9-46 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display General structural features (Figures 9.17 & 9.18) The DNA Double Helix The double-bonded structure is stabilized by 1. Hydrogen bonding between complementary bases A bonded to T by two hydrogen bonds C bonded to G by three hydrogen bonds 2. Base stacking Within the DNA, the bases are oriented so that the flattened regions are facing each other

55 9-47 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display General structural features (Figures 9.17 & 9.18) The DNA Double Helix There are two asymmetrical grooves on the outside of the helix 1. Major groove 2. Minor groove Certain proteins can bind within these grooves They can thus interact with a particular sequence of bases

56 9-48 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Figure 9.17

57 9-49 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Figure 9.18

58 9-55 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display To fit within a living cell, the DNA double helix must be extensively compacted into a 3-D conformation This is aided by DNA-binding proteins Refer to 9.21 This topic will be discussed in detail in Chapter 10 The Three-Dimensional Structure of DNA

59 9-56 Figure 9.21 DNA wound around histone proteins

60 9-57 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display The primary structure of an RNA strand is much like that of a DNA strand Refer to Figure 9.22 vs RNA strands are typically several hundred to several thousand nucleotides in length In RNA synthesis, only one of the two strands of DNA is used as a template RNA Structure

61 9-58 Figure 9.22

62 Table 10-4 Copyright © 2006 Pearson Prentice Hall, Inc.

63 9-59 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Although usually single-stranded, RNA molecules can form short double-stranded regions This secondary structure is due to complementary base- pairing A to U and C to G This allows short regions to form a double helix Different types of RNA secondary structures are possible Refer to Figure 9.23

64 9-60 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Figure 9.23 Also called hair-pin Complementary regions Noncomplementary regions Held together by hydrogen bonds Have bases projecting away from double stranded regions

65 9-61 Many factors contribute to the tertiary structure of RNA For example Base-pairing and base stacking within the RNA itself Interactions with ions, small molecules and large proteins Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display Figure 9.24 depicts the tertiary structure of tRNA phe The transfer RNA that carries phenylalanine Molecule contains single- and double- stranded regions These spontaneously interact to produce this 3-D structure Figure 9.24

66 Figure 10-1 Copyright © 2006 Pearson Prentice Hall, Inc.


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