Nucleic Acids

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Nucleic acids

Transcript of Nucleic Acids

  • Nucleic Acids

  • Nucleic Acids Polynucleotides whose primary structure

    contains a code or set of directions by which they can duplicate themselves and guide the synthesis of proteins.

    2 types of nucleic acids:

    1. DNA found mainly in the nucleus, contains genetic codes to make RNA

    2. RNA found in the cytoplasm although synthesized in the nucleus, contains codes to make proteins

  • What are the monomers of polynucleotides?

    Polynucleotides are composed of nucleotides.

    PHOSPATE SUGAR

    Ribose or

    Deoxyribose

    NUCLEOTIDE

    BASE

    PURINES PYRIMIDINES

    Adenine (A)

    Guanine(G)

    Cytocine (C)

    Thymine (T)

    Uracil (U)

  • The sugar: Ribose for RNA & 2-deoxyribose for DNA

    RIBOSE DEOXYRIBOSE

    CH2OH

    H

    OH

    C

    C

    OH OH

    C

    O

    H HH

    C

    CH2OH

    H

    OH

    C

    C

    OH H

    C

    O

    H HH

    C

  • The nucleobases are purine or pyrimidine derivatives

  • Some unusual nucleobases (found principally in tRNA)

  • Nucleoside = base + sugar

  • Purine Nucleotides

  • Purine Nucleotides

  • Pyrimidine Nucleotides

  • Pyrimidine Nucleotides

  • Pyrimidine Nucleotides

  • How do nucleotides combine to give nucleic acids?

    By formation of an ester bond from one nucleotide to the next. Result: 2 ester bonds (3 of one nucleoside and 5 of the next nucleoside), a 3,5-phosphodiester bond.

  • How do nucleotides combine to give nucleic acids?

    By formation of an ester bond from one nucleotide to the next. Result: 2 ester bonds (3 of one nucleoside and 5 of the next nucleoside), a 3,5-phosphodiester bond.

  • The Structure of DNA In terms of amounts, A=T and G=C (Chargaffs

    Rule, 1950, Austrian chemist who taught in Columbia U.). This led to the conclusion that the DNA structure is composed of 2 polynucleotides forming a helix (Watson & Crick, 1952).

    What stabilizes the helix? H-bonds between bases in opposite chains & base stacking

    Russian chemist Phoebus Levene: discovered the phosphate-sugar-base order in nucleotide, discovered the sugar (ribose) component of RNA, discovered the sugar (deoxyribose) component of DNA

  • The Structure of DNA Chargaffs 2nd Rule

  • The Structure of DNA Base Pairing

  • Are there other conformations of the double helix?

  • Interactions of bases: base stacking

  • In standard B-DNA, each base pair is rotated 32 wrt the preceding base pair: optimal for maximal base pairing, not optimal for maximal overlap of bases, H2O gets into minor groove

  • Propeller-twist: optimal for maximal base overlap, less optimal for maximal base pairing, H2O is eliminated from minor groove

  • Supercoiling in Prokaryotes

  • Supercoiling in Prokaryotes

  • Supercoiling in Eukaryotes

  • Denaturation of DNA Involves breaking of H-bonds between base

    pairs and the disruption of stacking interactions.

    Usually carried out by heating the DNA in solution.

    Greater amount of G-C pairs, higher melting temperature of a DNA molecule.

    G-C pairs are also more hydrophobic, so they stack better, so higher melting temp.

  • The principal kinds of RNA