1. DNA Structure and Analysis

2. What is the Genetic Material?
Genetics has a long and storied history
Many think of genetics beginning with the discovery of the double helix, but mankind has been studying and manipulating DNA for thousands of years
Although the details for this were not understood until the middle of the 20th Century
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3. Early DNA Experiments

4. Assyrian date palm pollination

5. What is behind this phenomenon?
DNA!

6. The Discovery DNA
As you have seen from the videos, the story of the discovery of the structure of DNA is amazing
But there is more to the story than seen in the videos and the story of the discovery of DNA as the genetic material is as fascinating as that of Watson, Crick, and Franklin
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7. 10.1 The Genetic Material Must Exhibit Four Characteristics
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8. For a molecule to serve as the genetic material, it must be able to
Section 10.1
For a molecule to serve as the genetic material, it must be able to
replicate
store information
express information
allow variation by mutation
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9. Section 10.1
The central dogma of molecular genetics is that DNA makes RNA (transcription), which makes proteins (translation) (Figure 10.1)
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10. Figure 10.1 Simplified view of the central dogma describing information flow involving DNA, RNA, and proteins within cells.
Figure 10.1
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11. 10.2 Until 1944, Observations Favored Protein as the Genetic Material
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12. In the 1940s, many geneticists favored proteins
Section 10.2
The genetic material is physically transmitted from parent to offspring
Proteins and nucleic acids were the major candidates for the genetic material
In the 1940s, many geneticists favored proteins
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13. Proteins are more diverse and abundant in cells
Section 10.2
Proteins are more diverse and abundant in cells
They were the subject of the most active areas of genetic research, with more known about proteins than nucleic acid chemistry
DNA was thought to be too simple to be the genetic material, with only four types of nucleotides as compared to the 20 different amino acids of proteins
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14. 10.3 Evidence Favoring DNA as the Genetic Material Was First Obtained during the Study of Bacteria and Bacteriophages
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15. Section 10.3
Griffith (1927) showed that avirulent strains of Diplococcus pneumoniae could be transformed to virulence (Figure 10.2)
He speculated that the transforming principle could be part of the polysaccharide capsule or a compound required for capsule synthesis
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16. Figure 10. 2 Griffith’s transformation experiment
Figure 10.2 Griffith’s transformation experiment. The photographs show bacterial colonies containing cells with capsules (type IIIS) and without capsules (type IIR).
Figure 10.2
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17. Section 10.3
Avery, MacLeod, and McCarty demonstrated that the transforming principle was DNA and not protein (Figure 10.3)
In their 1944 publication they stated, "The evidence presented supports the belief that a nucleic acid of the deoxyribose type is the fundamental unit of the transforming principle of Pneumococcus Type III."
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18. Figure 10.3 Summary of Avery, MacLeod, and McCarty’s experiment, which demonstrated that DNA is the transforming principle.
Figure 10.3
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19. Section 10.3
Hershey and Chase (1952), using Escherichia coli and an infecting virus (bacteriophage T2), demonstrated that DNA, and not protein, is the genetic material
Using radioisotope 32P and 35S, Hershey and Chase demonstrated that DNA enters the bacterial cell during infection and directs viral reproduction (Figures 10.4 and 10.5)
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20. Figure 10.4 Reproductive cycle of a T-even bacteriophage, as known in The electron micrograph shows an E. coli cell during infection by numerous phages.
Figure 10.4
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21. Figure 10.5 Summary of the Hershey–Chase experiment demonstrating that DNA, and not protein, is responsible for directing the reproduction of phage T2 during the infection of E. coli.
Figure 10.5
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22. 10.4 Indirect and Direct Evidence Supports the Concept that DNA Is the Genetic Material in Eukaryotes
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23. Protein is abundant in the cytoplasm and DNA is not
Section 10.4
Protein is abundant in the cytoplasm and DNA is not
Mitochondria and chloroplast perform genetic function, and DNA is also part of these organelles
DNA is found only where the primary genetic function occurs
This provides indirect evidence for DNA as the genetic material
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24. Again, this provides indirect evidence for DNA as the genetic material
Section 10.4
UV light is capable of inducing mutations in the genetic material and is most mutagenic at a wavelength of 260 nm
DNA and RNA absorb UV light most strongly at 260 nm, but protein absorbs most strongly at 280 nm, a wavelength at which no significant mutagenic effects are observed
Again, this provides indirect evidence for DNA as the genetic material
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25. 10.5 RNA Serves as the Genetic Material in Some Viruses
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26. Some viruses have an RNA core rather than a DNA core
Section 10.5
Some viruses have an RNA core rather than a DNA core
Experiments with tobacco mosaic virus (1956) demonstrated that RNA serves as the genetic material for these viruses
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27. Replication of the viral RNA is dependent on RNA replicase
Section 10.5
Replication of the viral RNA is dependent on RNA replicase
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28. 10.6 Knowledge of Nucleic Acid Chemistry Is Essential to the Understanding of DNA Structure
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29. Nucleotides are the building blocks of DNA They consist of
Section 10.6
Nucleotides are the building blocks of DNA
They consist of
a nitrogenous base
a pentose sugar
a phosphate group
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30. There are two kinds of nitrogenous bases
Section 10.6
There are two kinds of nitrogenous bases
Purines
Adenine (A)
Guanine (G)
Pyrimidines
Cytosine (C)
Thymine (T)
Uracil (U) (Figure 10.7)
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31. Figure 10.7 (a) Chemical structures of the pyrimidines and purines that serve as the nitrogenous bases in RNA and DNA. The nomenclature for numbering carbon and nitrogen atoms making up the two bases is shown within the structures that appear on the left. (b) Chemical ring structures of ribose and 2-deoxyribose, which serve as the pentose sugars in RNA and DNA, respectively.Web Tutorial 10.1DNA Structure
Figure 10.7
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32. Figure 10.7a (a) Chemical structures of the pyrimidines and purines that serve as the nitrogenous bases in RNA and DNA. The nomenclature for numbering carbon and nitrogen atoms making up the two bases is shown within the structures that appear on the left. (b) Chemical ring structures of ribose and 2-deoxyribose, which serve as the pentose sugars in RNA and DNA, respectively.Web Tutorial 10.1DNA Structure
Figure 10.7a
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33. Figure 10.7b (a) Chemical structures of the pyrimidines and purines that serve as the nitrogenous bases in RNA and DNA. The nomenclature for numbering carbon and nitrogen atoms making up the two bases is shown within the structures that appear on the left. (b) Chemical ring structures of ribose and 2-deoxyribose, which serve as the pentose sugars in RNA and DNA, respectively.Web Tutorial 10.1DNA Structure
Figure 10.7b
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34. DNA and RNA both contain A, C, and G Only DNA contains T
Section 10.6
DNA and RNA both contain A, C, and G
Only DNA contains T
Only RNA contains U
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35. RNA contains ribose as its sugar DNA contains deoxyribose
Section 10.6
RNA contains ribose as its sugar
DNA contains deoxyribose
(Figure 10.7b)
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36. A nucleoside contains the nitrogenous base and the pentose sugar
Section 10.6
A nucleoside contains the nitrogenous base and the pentose sugar
A nucleotide is a nucleoside with a phosphate group added (Figure 10.8)
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37. Figure 10.8 Structures and names of the nucleosides and nucleotides of RNA and DNA.
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38. Section 10.6
The C-5' position is the location of the phosphate group on a nucleotide
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39. Section 10.6
Nucleotides can have one, two, or three phosphate groups and are called NMPs, NDPs, and NTPs, respectively (Figure 10.9)
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40. Figure 10.9 Basic structures of nucleoside diphosphates and triphosphates, as illustrated by deoxythymidine diphosphate and deoxyadenosine triphosphate
Figure 10.9
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41. Section 10.6
Nucleotides are linked by a phosphodiester bond between the phosphate group at the C-5' position and the OH group on the C-3' position (Figure 10.10)
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42. Figure (a) Linkage of two nucleotides by the formation of a – phosphodiester bond, producing a dinucleotide. (b) Shorthand notation for a polynucleotide chain.
Figure 10.10
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43. Figure 10.10a (a) Linkage of two nucleotides by the formation of a – phosphodiester bond, producing a dinucleotide. (b) Shorthand notation for a polynucleotide chain.
Figure 10.10a
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44. Figure 10.10b (a) Linkage of two nucleotides by the formation of a – phosphodiester bond, producing a dinucleotide. (b) Shorthand notation for a polynucleotide chain.
Figure 10.10b
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45. 10.7 The Structure of DNA Holds the Key to Understanding Its Function
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46. Section 10.7
Chargaff (1949–1953) showed that the amount of A is proportional to T and the amount of C is proportional to G, but the percentage of C + G does not necessarily equal the percentage of A + T (Table 10.3)
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47. Table 10.3 DNA Base Composition Data
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48. Section 10.7
X-ray diffraction studies by Rosalind Franklin (1950–1953) of DNA showed a 3.4 angstrom periodicity, characteristic of a helical structure (Figure 10.11)
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49. Figure X-ray diffraction photograph of the B form of purified DNA fibers. The strong arcs on the periphery show closely spaced aspects of the molecule, providing an estimate of the periodicity of nitrogenous bases, which are 3.4 Å apart. The inner cross pattern of spots shows the grosser aspect of the molecule, indicating its helical nature.
Figure 10.11
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50. Section 10.7
Watson and Crick (1953) proposed that DNA is a right-handed double helix in which the two strands are antiparallel and the bases are stacked on one another
The two strands are connected by A-T and G-C base pairing, and there are 10 base pairs per helix turn (Figure 10.12)
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51. Figure 10. 12 (a) The DNA double helix as proposed by Watson and Crick
Figure (a) The DNA double helix as proposed by Watson and Crick. The ribbonlike strands constitute the sugar-phosphate backbones, and the horizontal rungs constitute the nitrogenous base pairs, of which there are 10 per complete turn. The major and minor grooves are apparent. The solid vertical bar represents the central axis. (b) A detailed view depicting the bases, sugars, phosphates, and hydrogen bonds of the helix. (c) A demonstration of the antiparallel nature of the helix and the horizontal stacking of the bases.
Figure 10.12
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52. Figure 10.12b (a) The DNA double helix as proposed by Watson and Crick. The ribbonlike strands constitute the sugar-phosphate backbones, and the horizontal rungs constitute the nitrogenous base pairs, of which there are 10 per complete turn. The major and minor grooves are apparent. The solid vertical bar represents the central axis. (b) A detailed view depicting the bases, sugars, phosphates, and hydrogen bonds of the helix. (c) A demonstration of the antiparallel nature of the helix and the horizontal stacking of the bases.
Figure 10.12b
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53. Section 10.7
The A-T and G-C base pairing provides complementarity of the two strands and chemical stability to the helix
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54. Section 10.7
A-T base pairs form two hydrogen bonds, and G-C base pairs form three hydrogen bonds (Figure 10.14)
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55. Figure 10. 14 Ball-and-stick models of and base pairs
Figure Ball-and-stick models of and base pairs. The dashes (– – –) represent the hydrogen bonds that form between bases.
Figure 10.14
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56. Section 10.7
The arrangement of sugars and bases along the axis provides another stabilizing factor
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57. 10.8 Alternative Forms of DNA Exist
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58. Section 10.8
Under different conditions of isolation, different conformations of DNA are observed
The Watson-Crick DNA model of B-DNA is seen under aqueous, low-salt conditions and is believed to be the biologically significant conformation
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59. It is doubtful that A-DNA occurs in vivo
Section 10.8
A-DNA is slightly more compact than B-DNA (Figure 10.15) and is prevalent under high-salt or dehydration conditions
It is doubtful that A-DNA occurs in vivo
C-DNA, D-DNA, E-DNA, and P-DNA are also right-handed forms of DNA that are less compact than B-DNA
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60. Figure The top half of the figure shows computer-generated space-filling models of B-DNA (left), A-DNA (center), and Z-DNA (right). Below is an artist’s depiction illustrating the orientation of the base pairs of B-DNA and A-DNA. (Note that in B-DNA the base pairs are perpendicular to the helix, while they are tilted and pulled away from the helix in A-DNA.)
Figure 10.15
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61. Figure 10.15a The top half of the figure shows computer-generated space-filling models of B-DNA (left), A-DNA (center), and Z-DNA (right). Below is an artist’s depiction illustrating the orientation of the base pairs of B-DNA and A-DNA. (Note that in B-DNA the base pairs are perpendicular to the helix, while they are tilted and pulled away from the helix in A-DNA.)
Figure 10.15a
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62. Figure 10.15b The top half of the figure shows computer-generated space-filling models of B-DNA (left), A-DNA (center), and Z-DNA (right). Below is an artist’s depiction illustrating the orientation of the base pairs of B-DNA and A-DNA. (Note that in B-DNA the base pairs are perpendicular to the helix, while they are tilted and pulled away from the helix in A-DNA.)
Figure 10.15b
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63. Z-DNA forms a left-handed double helix (Figure 10.15)
Section 10.8
Z-DNA forms a left-handed double helix (Figure 10.15)
DNA might have to assume a structure other than the B form for some of its genetic functions; however, this awaits further study
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64. 10.9 The Structure of RNA Is Chemically Similar to DNA, but Single Stranded
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65. Section 10.9 In RNA, the sugar ribose replaces deoxyribose of DNA and
uracil replaces thymine of DNA
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66. In addition, some viruses have a double-stranded RNA genome
Section 10.9
Most RNA is single stranded, although some RNAs form double-stranded regions as they fold into different secondary structures
In addition, some viruses have a double-stranded RNA genome
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67. Section 10.9
There are three classes of cellular RNAs that function during expression of genetic information
messenger RNA (mRNA)
ribosomal RNA (rRNA)
transfer RNA (tRNA)
These all originate as complementary copies of one of the two DNA strands during transcription
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68. Section 10.9
The characteristics of these RNAs in prokaryotic and eukaryotic cells are summarized in Table 10.4
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69. Table 10.4 RNA Characterization
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70. rRNAs are structural components of ribosomes for protein synthesis
Section 10.9
rRNAs are structural components of ribosomes for protein synthesis
mRNAs are the template for protein synthesis
tRNAs carry amino acids for protein synthesis
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71. HOMEWORK Part I: Answer the following questions from the chapter 10 problems. Part II: Complete Mastering Assignment #1 #3 #5
Post your answers in your Box Folder. ID file as “Ch 10 DNA Structure Homework”
Due Feb 17 Monday, 9:00 AM
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