Key info on shape size came from X ray crystallography done by Maurice Wilkins

Key info on shape size came from x ray

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Key info on shape & size came from X-ray crystallography done by Maurice Wilkins & Rosalind Franklin. The crystallography showed: - DNA is helical -Its width is 2 nanometers (nm) -The bases are stacked 0.34 nm apart Watson & Crick got their inspiration from wire models: They figured out that DNA consists of: - 2 strands of nucleotide polymers with: -bases on the inside -sugar-phosphate backbone on the outside
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Hydrogen bonds hold the bases--and thus the two polymer strands of the double helix--together 2 H-bonds occur between A & T 3 H-bonds occur between G & C Hence GC pairs provide more strength than AT pairs . This explains Chargaff’s Rule: The amount of A=T, and the amount of G=C
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DNA structure explains how genetic information is stored. It explains what genes are. The nucleotides A, T, G, & C act like an alphabet, making sentences that describe genetic information for cells. Genes are segments of DNA that code for a particular function or character. The sequence of nucleotides instructs each cell what to make and when to make it.
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DNA structure also explains how DNA is replicated – i.e., how genetic information is reproduced and transferred from generation to generation in organisms Duplexed DNA : two strands held by together by H-bonds Single-stranded DNA when H-bonds are broken Single-strands act as templates for new DNA strands. They join with complementary nucleotides to form exactly replicated new strands Newly copied DNA (light blue) H-bonded to template DNA (dark blue) DNA structure provides a template (a mould) for replication
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Semi-conservative Replication Replication is semi-conservative i.e., original strands (dark blue template strands) combine with new strands (light blue). In the next generation of replicated DNA, both original dark blue and newer light blue strands act as templates.
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Details of Replication Highly reactive (energized) nucleoside triphosphates (which are closely related to ATP) are joined to growing DNA strands.
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Details of Replication, continued Some nomenclature A nucleotide = phosphate & sugar & base A nucleoside = sugar & base (without phosphate) Nucleoside triphosphates are related to ATP, but have a deoxyribose sugar. Like ATP, they are very reactive.
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The polarity of DNA strands Note the numbering of carbons on the deoxyribose sugar of DNA The phosphate group of the nucleotide (in this case Adenine) is attach to the 5’ carbon The 3’ carbon of the adenine is attached to the phosphate group of the next nucleotide C 5’ The base attaches to the 1’ carbon
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  • Fall '19
  • DNA, Frederick Griffith

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