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Transcript of NUCLEIC ACIDS INTRODUCTION - kadima/CHE525/NUCLEIC ACIDS_INTRODUCTI · PDF fileNUCLEIC...

  • 1

    NUCLEIC ACIDS

    An INTRODUCTION

    Two classes of Nucleic Acids

    Deoxynucleic Acids (DNA) Hereditary molecule of all cellular life Stores genetic information (encodes) Transmits genetic information Information on protein sequence is encoded

    in DNA and translated by the help of messenger Ribonucleic Acid (mRNA)

    Ribonucleic Acids Encode and Translate information on DNA to

    proteins

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    Composition and Structure of Nucleic Acids

    Nucleobases Derivatives of purine and pyrimidine bases

    Sugars Phosphoric acid DNA nucleobases

    Adenine (A) and Guanine (G) Tymine (T) and Cytosine (C)

    RNA nucleobases A and G Uracyl (U) and Cytosine (C)

    Nucleobases

    Uracyl thymine without the methyl group

    DNA nucleobasesAdenine (A) and Guanine (G)Tymine (T) and Cytosine (C)

    RNA nucleobasesA and GUracyl (U) and Cytosine

    1

    7

    3 9 1

    6

    2

    5

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    Sugars-D-ribose and -D-deoxyribose

    DNA Nucleosides

    Base (N9 or N1 atom) + sugar (C1atom) N-glycosidic bond

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    Building Blocks: Nucleotides

    Nucleoside + phosphate group(s)

    5-hydroxylic group of sugar phosphate

    Ester bond

    Polynucleotides

    Backbone : sugar + phosphate Side groups: nucleobases Reading from

    From Nucleotide with free phosphate group (5end)

    To nucleotide with free 3hydroxyl group (the 3 end)

    A T G C sugar phosphate sugar phosphate sugar phosphate sugar ...

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    Double Strand Formation

    Base Pairing

    Double strand DNA is inherently very sensitive/ fragile

    Strands Pairing

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    The Double Helix

    Denatured during replication and mRNA synthesisDenatured during PCR (amplification of DNA)

    Levels of Structural Organization

    Primary Sequence of nucleotide Name of nucleobases used : ATCT

    Secondary Double stranded helix structure

    Tertiary Folding of the double helix Example: super coiled

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    Structure of RNA Single strand Folds on itself thus allowing pairing of

    bases

    Synthesis of Proteins

    Procaryote cell Eucaryote cell

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    Synthesis of Proteins

    Synthesis of Proteins1. Transcription

    One strand of the DNA double helix is used as a template by the RNA polymerase to synthesize a messenger RNA (mRNA).

    mRNA migrates from the nucleus to the cytoplasm. mRNA goes through different types of maturation including one called

    splicing when the non-coding sequences are eliminated. The coding mRNA sequence can be described as a unit of three

    nucleotides called a codon.2. Translation

    The ribosome binds to the mRNA at the start codon (AUG) that is recognized only by the initiator tRNA.

    The ribosome proceeds to the elongation phase of protein synthesis. During this stage, complexes, composed of an amino acid linked to tRNA, sequentially bind to the appropriate codon in mRNA by forming complementary base pairs with the tRNA anticodon.

    The ribosome moves from codon to codon along the mRNA. Amino acids are added one by one, translated into polypeptidic sequences dictated by DNA and represented by mRNA.

    At the end, a release factor binds to the stop codon, terminating translation and releasing the complete polypeptide from the ribosome.

    One specific amino acid can correspond to more than one codon. The genetic code is said to be degenerate.

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    Synthesis of Proteins: Genetic Code

    Protein Synthesis Folding, disulfide bridges formation, post-

    translational modification

    Post-translational modifications Not determined by DNA sequence Cleavage of amino acids Phosphorylation Acetylation glycosylation

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    Analytical Challenges for the Analysis of Biological Macromolecules

    Inherent sensitivity

    Both proteins and nucleic acid 3D structure are very sensitive to environmental conditions such as pH, ionic strength, solvent composition

    Why? stabilized by H-bonds, other dipole-dipole interactions, electrostatic interactions, van der Waals interactions

    Problems Denaturation Crystallization challenges

    Analytical Challenges for the Analysis of Biological Macromolecules

    Size of macromolecules Several signals that must be resolved and analyzed Complex three dimensional Structure NMR challenges

    Number of macromolecules in real samples Separation methods Methods for selective detection

    Amount of sample Sensitivity must be high Amplification