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4.2 DNA STRUCTURE

4.2 DNA STRUCTURE . DNA is slightly acidic and composed of large amounts of phosphorus and nitrogen. In the 1920’s it was determined that DNA is comprised of three main components A deoxyribose sugar A phosphate group A nitrogenous base. Nitrogenous bases are split into two groups:

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4.2 DNA STRUCTURE

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  1. 4.2 DNA STRUCTURE • DNA is slightly acidic and composed of large amounts of phosphorus and nitrogen. • In the 1920’s it was determined that DNA is comprised of three main components • A deoxyribose sugar • A phosphate group • A nitrogenous base

  2. Nitrogenous bases are split into two groups: • Purines • Double ringed structures • Adenine and Guanine • Pyrimidines • Single ringed structures • Thymine and Cyosine • Chargaff’s Rule: proportion A= proportion T, proportion G=proportion C • A purine will always bond with a pyrimidine

  3. NUCLEOTIDE STRUCTURE • sugar + phosphate + nitrogenous base

  4. Sugar Component • 5 carbon deoxyribose sugar with 4 carbons attached to an oxygen in a ring with the 5th carbon extending out. • Deoxyribose: lost the hydroxyl group (OH) on 2 ‘ carbon • Carbons numbered clockwise with nitrogenous base attached to 1’ by a glycosyl bond and phosphate group attached to 5’ with an ester bond.

  5. Glycosyl Bond: • A bond between a sugar and another organic molecule by way of an intervening N or O atom • Phosphate Group: a group of 4 oxygen atoms surrounding a central phosphorous atom found in the backbone of DNA • Nitrogenous Base: an alkaline, cyclic molecule containing N

  6. DNA Structure Details • Rosalind Franklin and Maurice Wilkins • Used x-ray diffraction to determine DNA structure. • Wilkins took Franklin’s unpublished results to James Watson and Francis Crick. • Watson and Crick took this information to build their double-helix model. • Watson, Crick and Wilkins were awarded the Nobel Prize in 1962 for their efforts… • Composed of two antiparallel strands of nucleotides • One strand runs 5’ to 3’, other runs 3’ to 5’ • 3’ end terminates with hydroxyl group of deoxyribose. • 5’ end terminates with phosphate group • 5’ – ATGCCGTTA – 3’3’ – TACGGCAAT – 5’ • By convention only the 5’ to 3’ strand is written.

  7. Constant diameter of DNA is 2mm • Completes a complete helical turn every 3.4nm or every 10 nucleotides. • Turns in a clockwise direction • If purines bonded to each other, strand would be wider at some points and if pyrimidines bond to one another, strand would be narrower at some points. • Bases are bonded to one another with hydrogen bonds

  8. Antiparallel Nature of DNA Parallel but running in opposite directions 5’ end of one strand of DNA aligns with the 3’ end of the other strand in a double helix

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