1 And the RACE BEGINS! Once DNA was identified as the genetic molecule the race was on to determine its structure. The combined work of different researchers led to its discovery in February 1953.

2 Important Experiments of the 1950’sErwin Chargaff Analyzed the DNA of many living organisms. In every sample he found equal amounts of certain nitrogen bases.

3 Chargaff’s DNA Nucleotide Sample Testing Results

4 ADENINE (A) = THYMINE (T) CYTOSINE (C) = GUANINE (G) In every sample of DNA from every organism, the amount of ADENINE (A) = THYMINE (T) CYTOSINE (C) = GUANINE (G) Chargaff’s Base Pairing Rules

5 Chargaff’s Research ImplicationsChargaff finding explained how all organisms have the same universal DNA but still be so different. All organisms contain the same nitrogen bases in their DNA but the amount of each base is different for each organism.

6 2. Rosalind Franklin and Maurice WilkinsUsed a technique called x-ray crystallography to capture the first images of DNA which suggested that it had a spiral or helical shape and an even width.

7 Rosalind’s boss, Maurice Wilkins, showed her Photo 51 to other researchers without her knowledge.

8 . 3. James Watson and Francis Crick Based their model on other’s research. Used Franklin’s photograph of DNA and Chargaff’s rules of base pairing to develop a model of DNA.

9 In 1953 they published a paper in the scientific journal Nature.

10 Watson and Crick’s findingsDNA’s structure is: double stranded two strands complementary to each other shaped like a double helix structure would likely allow it to replicate /copy itself.

11 Awarded the the Nobel Prize in Medicine in 1962Francis Harry Compton Crick James Dewey Watson Maurice Hugh Frederick Wilkins

12 Rosalind Franklin died of cancer at the age of 38.Nobel Prize is not awarded posthumously.

13 KEY CONCEPT DNA structure is the same in all organisms.

14 Nucleic Acid StructureDNA and RNA are polymers made up of billions of repeating monomer units called nucleotides. Phosphate Sugar Nitrogen-containing base

15 Monomer - Nucleotide Polymer – DNA

16 Each Nucleotide is composed of 3 molecules bonded together Nucleotide Structure Each Nucleotide is composed of 3 molecules bonded together 1. Phosphate (P) 2. 5 Carbon Sugar (S) 3. Nitrogen-containing base Phosphate Sugar Nitrogen-containing base

17 Nucleotides are named for the nitrogen base they contain.Types of Nucleotides There are 5 types of nucleotides but each nucleic acid only contains 4 types. Nucleotides are named for the nitrogen base they contain. Nitrogen bases are grouped based on their ring structure.

18 Types of Nitrogen Bases in Nucleotidedepends on base1. Pyrimidines – Single ring structure *Cytosine -- C *Thymine – T (Only in DNA) *Uracil – U (Only in RNA) 2. Purines – Double ring structure *Guanine - G *Adenine - A .

19 Types of Nucleotides depend on their nitrogen base

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21 Explained Chargaff’s RuleBase Pairing in DNA– One purine (double ring) hydrogen bonds with one pyrimidine (single ring) Explained Chargaff’s Rule C G T A

22 Hydrogen bonds between the base pairs hold the two strands of DNA together in the double helixBase pairing allows the DNA molecule to maintain an even width along its entire length C G T A

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24 What makes each individual organism unique is the order of their base pairs – the base sequence - in their DNA.

25 LET’S COMPARE DNA TO RNA

26 Comparison of DNA and RNADNA RNA Name Deoxyribonucleic Acid Ribonucleic Acid Sugar type Deoxyribose Ribose Nitrogen Bases A,T,G,C A,U,G,C # of Strands Double stranded Single Stranded

27 DNA 2 antiparallel strandsThe sugar-phosphate backbone is connected by covalent bonds. Hydrogen bonds between base pairs hold strands together hydrogen bond covalent bond

28 RNA Single strand Ribose sugar Uracil instead of thymine

29 Functions of Nucleic AcidsDNA –the cell’s “blueprint” or recipe for making proteins RNA – 3 types. Each type has a specific job in making proteins.