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

History of DNA 1928: Griffith finds “transforming principle” material that changed the harmless bacteria into disease-causing bacteria Avery said that DNA must be the transforming principle or genetic material Hershey and Chase experiment with bacteriophages convinced scientists that the genetic material is DNA 4

DNA Discovery Early 1950’s Watson and Crick Used work of Hershey,Chase, Chagaff, Pauling and said that DNA was a double helix. In 1953 published paper that said that DNA was double helix, in which two strands of DNA wind around each other like a twisted ladder. 5

Rosalind Franklin During the same time that Watson and Crick were doing their research Franklin produced a x-ray photograph of DNA that indicated it was a helix. Her coworker Maurice Wilkins showed the data to Watson and Crick, which helped them discover DNA’s structure. 6

7 DNA Why do we study DNA? We study DNA for many reasons, e.g., its central importance to all life on Earth, medical benefits such as cures for diseases, better food crops.

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

9 The Shape of the Molecule DNA is a very long polymer. The basic shape is like a twisted ladder or zipper. This is called a double helix.

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

11 One Strand of DNA The backbone of the molecule is alternating phosphates and deoxyribose sugar The “rungs” are nitrogenous bases. phosphate deoxyribose bases

12 Nucleotides CC C O Phosphate O C C O -P O O O O O O O One deoxyribose together with its phosphate and base make a nucleotide. Nitrogenous base Deoxyribose

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

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

15 Two Kinds of Bases in DNA Pyrimidines are single ring bases.Pyrimidines are single ring bases. Purines are double ring bases.Purines are double ring bases. C C C C N N O N C C C C N N N N N C

16 Thymine and Cytosine are pyrimidines Thymine and cytosine each have one ring of carbon and nitrogen atoms.Thymine and cytosine each have one ring of carbon and nitrogen atoms. C C C C N N O N cytosine C C C C N N O O thymine C

17 Adenine and Guanine are purines Adenine and guanine each have two rings of carbon and nitrogen atoms.Adenine and guanine each have two rings of carbon and nitrogen atoms. C C C C N N N Adenine N N C C C C C N N O N Guanine N N C

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

19 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

20 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

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

22 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.

How does DNA make more DNA? During the S phase of mitosis. Enzyme called DNA helicase causes the DNA molecule to ‘unzip” 23

Replication cont. As the molecule unzips, free nucleotides from the nucleoplasm bond to the single strands. Enzyme DNA polymerase bonds these new nucleotides into a chain. This process continues until the entire molecule has been unzipped and replicated. After the DNA molecule has been replicated the end result is a new strand of DNA that is a complement to the original.(2 strands identical to the original) 24

25 Central Dogma Process DNA- RNA- PROTEINS