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Nucleic Acids

Nucleic Acids. Components of DNA. DNA is composed of four kinds of nucleotides , each of which consists of – a five carbon sugar ( deoxyribose ) – a phosphate group (PO4-) – one of four bases – adenine (A), guanine (G), thymine (T), or cytosine (C). Nucleotides.

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Nucleic Acids

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  1. Nucleic Acids

  2. Components of DNA DNA is composed of fourkinds of nucleotides, eachof which consists of– a five carbon sugar (deoxyribose) – a phosphate group(PO4-) – one of four bases – adenine(A), guanine (G), thymine(T), or cytosine (C)

  3. Nucleotides Thymine and Cytosine Adenine and Guanine

  4. Edwin Chargaff, in 1949,noted two critical bits of data

  5. The four kinds of nucleotide bases makingup a DNA molecule differ in relativeamounts from species to species

  6. Rosalind Franklin Used x-ray diffraction techniques to produce images of DNA molecules. She concluded: • DNA exists as a long, thin molecule of uniform diameter. • The structure is highly repetitive. • DNA is helical.

  7. Patterns of Base Pairing Watson and Crick used numerous sources of data to build models of DNA.

  8. Patterns of Base Pairing The bases were hydrogen bonded (a weak bond) together in the center of the helix. – T (a pyrimidine) had twohydrogen bonds with A (apurine) – C (a pyrimidine) had threehydrogen bonds with G (apurine)

  9. Patterns of Base Pairing The backbone wasmade of chains ofdeoxyribose sugarcovalently bonded (astrong bond) tophosphate groups. The phosphate groupis bonded to the 3’carbon of onedeoxyribose, and the5’ carbon of another.

  10. Patterns of Base Pairing Each sugar ofthe backbone iscovalentlybonded to thenitrogenousbase off ofcarbon 1.

  11. Patterns of Base Pairing There are 10base pairsper turn ofthe helix.

  12. Patterns of Base Pairing The two sides are anti-parallel,meaning that the sugar andphosphates are running inopposite directions.• Each side ends in a phosphate(5’ end) and a sugar (3’ end) Since the sides are anti-parallel,one side goes in the 3' to 5'direction, and the other goes inthe 5' to 3' direction. The base pairing is constant for all species, but the sequence of base pairs in a nucleotide strand is different from one species to the next.

  13. Where is DNA Located? Prokaryotes • bacteria and Archaea • Circular DNA ina region calledthe nucleoid • Plasmid Eukaryotes • Inside the nucleus • Linear • Highly coiled • Set of eight proteins called histones act as spools to wind the DNA into units called nucleosomeswhich form additional loops called a chromosome.

  14. Where is DNA Located? Inside mitochondria and chloroplasts • Circular • “Naked” – notassociated withprotein

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