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History Before the 1940’s scientists didn’t know what material caused inheritance. They suspected it was either DNA or proteins.

History A series of experiments proved that DNA was the genetic material responsible for inheritance.

History In 1952, Alfred Hershey and Martha Chase did an experiment using a virus that infects E. coli bacteria. The experiment proved that DNA and not protein is the factor that influences inheritance.

History Erwin Chargaff discovered the base pairing rules and ratios for different species. Adenine pairs with Thymine Cytosine pairs with Guanine.

History Rosalind Franklin & Maurice Wilkins had taken the 1 st pictures of DNA using X-ray crystallization

This proved that DNA had a helical shape.

History The Nobel Prize in Medicine 1962 Francis Harry Compton Crick James Dewey Watson Maurice Hugh Frederick Wilkins Rosalind Franklin (Died of cancer 1958)

Wilkins has become a historical footnote and Watson & Crick are remembered as the Fathers of DNA WatsonCrick

11 The Double Helix Molecule The DNA double helix has two strands twisted together.

13 DNA DNA.DNA is often called the blueprint of life. In simple terms, DNA contains the instructions for making proteins within the cell.

14 Chromosomes and DNA Our genes are on our chromosomes. Chromosomes are made up of a chemical called DNA.

15 DNA Stands for Deoxyribonucleic acid nucleotidesMade up of subunits called nucleotides Nucleotide made of:Nucleotide made of: Phosphate group 1.Phosphate group 5-carbon sugar 2.5-carbon sugar Nitrogenous base 3.Nitrogenous base

16 One Strand of DNA The backbone of the molecule is alternating phosphates and deoxyribose sugar The teeth are nitrogenous bases. phosphate deoxyribose bases

17 One Strand of DNA One strand of DNA is a polymer of nucleotides. One strand of DNA has many millions of nucleotides. nucleotide

DNA O O=P-O OPhosphate Group Group N Nitrogenous base (A, T, G, C) (A, T, G, C) CH2 O C1C1 C4C4 C3C3 C2C2 5 Sugar Sugar(deoxyribose)

19 Four nitrogenous bases Cytosine C Thymine T Adenine A Guanine G DNA has four different bases:

Nitrogen Bases 2 types of Nitrogen Bases –Purines Double ring –G & A –Pyrimidines Single ring –C & U & T PGA CUT PY A or G T or C

21 Two Stranded DNA Remember, DNA has two strands that fit together something like a zipper. The teeth are the nitrogenous bases but why do they stick together?

22 C C C C N N O N C C C C N N O N N N C Hydrogen Bonds The bases attract each other because of hydrogen bonds. Hydrogen bonds are weak but there are millions and millions of them in a single molecule of DNA. The bonds between cytosine and guanine are shown here with dotted lines

23 Hydrogen Bonds, Hydrogen Bonds, cont. When making hydrogen bonds, cytosine always pairs up with guanine Adenine always pairs up with thymine Adenine is bonded to thymine here C C C C N N N N N C C C C C N N O O C

24 Chargaff’s Rule: Adenine and Thymine always join together A T Cytosine and Guanine always join together C G

DNA DNA is a double- stranded molecule. The strands are connected by complementary nucleotide pairs (A-T & C-G) like rungs on a ladder. The ladder twists to form a double helix.

DNA - double helix P P P O O O P P P O O O G C TATA

27 Question: Adenine CytosineIf there is 30% Adenine, how much Cytosine is present?

28 Answer: CytosineThere would be 20% Cytosine Adenine (30%) = Thymine (30%)Adenine (30%) = Thymine (30%) Guanine (20%) = Cytosine (20%)Guanine (20%) = Cytosine (20%) Therefore, 60% A-T and 40% C-GTherefore, 60% A-T and 40% C-G

29 DNA by the Numbers Each cell has about 2 m of DNA. The average human has 75 trillion cells. The average human has enough DNA to go from the earth to the sun more than 400 times. DNA has a diameter of only m. The earth is 150 billion m or 93 million miles from the sun.