DNA DNA is the only organic molecule capable of duplicating itself which allows cells to divide which allows for life to exist. DNA is contained in the nucleus of eukaryotic cells in long strands called chromosomes. (winding)

DNA STRUCTURE a PHOSPHATE group, and one of four NITROGENOUS bases: The basic unit of DNA is the NUCLEOTIDE. It is made up of a 5 carbon sugar molecule called DEOXYRIBOSE, a PHOSPHATE group, and one of four NITROGENOUS bases: Adenine, Thymine, Guanine, and Cytosine.

DNA STRUCTURE DNA forms long chains as phosphates on one nucleotide bond to the OH on the sugar of another nucleotide. The bases stick out to the side.

DNA STRUCTURE Two strands of DNA are able to stick together because of hydrogen bonding between bases; one strand running one way and the other running the other way.

DNA STRUCTURE The bonding is VERY specific: Adenine bonds to Thymine  Guanine bonds to Cytosine (Chargaff’s rule) Thymine and Cytosine are called pyrimidines. Adenine and Guanine are purines.

DNA STRUCTURE So if T matches always with A and C matches with G, the two strands can be “complementary”. A T G C LEADING STRAND (5’ => 3’) A T G C A G T C T G G T C A A COMPLEMENTARY STRAND (3’<= 5’) (LAGGING STRAND) What is the complementary sequence in the bottom strand?

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