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Always add to 3 end 19 dna is a double helix crick

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Unformatted text preview: ol end. always add to 3’ end 19 DNA is a double helix Crick Wilkins (the boss) Franklin Watson First proposed by James Watson and Francis Crick in a 1953 paper Know these 2 names 20 DNA is a double helix Rosalind Franklin Know this name First proposed by James Watson and Francis Crick in a 1953 paper Based on both X-ray diffraction data, and studies of the chemical composition of DNA, including the finding that the ratio of both A:T and G:C is 1:1 21 Complementary base pairing Adenine and Thymine - 2 hydrogen bonds Guanine and Cytosine - 3 hydrogen bonds 22 The structure of DNA -anti-parallel strands held together by hydrogen bonding between the base pairs. -one complete turn every 34Å 3.4nm -ratio of A to T is always 1:1 as is the ratio of G to C -final piece of the DNA model puzzle 23 not perfectly curved The structure of DNA upward to the right curved. 24 if the known % of A is 12%, what is the % of cytosine? 38% (100% total) The Double Helix may assume alternative forms The majority of naturally occurring DNA molecules have the classic Watson-Crick structure. These are known as B-form DNA and spiral to the right. Some nucleotide sequences (alternating purine:pyrimidine basepair repeats) cause DNA to assume a Z-form, in which case the helix spirals to the left and the backbone takes on a zigzag shape 25 Alternative DNA configurations A form dehydrated B form Z form (1979)26 left handed helix, Wikimedia commons sugars and phosphate arent on backbone The biological role of Z DNA has yet to be defined, but it appears to be present in certain highly active genes. Proteins t...
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