Biological Molecules

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Author:
sarahnym
ID:
158166
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Biological Molecules
Updated:
2012-06-11 11:43:17
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Nucleic Acids
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Biological Molecules - Nucleic Acids
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  1. NUCLEIC ACIDS


    • genetic materials on which genetic information are encoded
    • consist of nucleotides (monomers), which consist of pentose sugar, nitrogenous base and phosphate group
    • 2 types: DNA & RNA
  2. DNA
    - double helix structure consisting of 2 antiparallel polynucleotide chains
    - monomer: deoxyribonucleotides

    Deoxyribose sugar: C2 linked to -H instead of -OH (in RNA)

    • Nitrogenous base:
    • Purines (2 rings) - Adenine & Guanine
    • Pyrimidines (1 ring) - Thymine, Cytosine & Uracil (RNA)

    • Phosphate group:
    • bonded to C5, formed by condensation reaction between H3PO4 & C5.
  3. Nucleoside = sugar + base
    Nucleotide = sugar + base + 1 phosphate group

    Nucleoside diphosphate = sugar + base + 2 phosphate groups
    Nucleoside triphosphate = sugar + base + 3 phosphate groups
  4. FORMATION OF POLYNUCLEOTIDES

    • 5' phosphate group of 1 free nucleoside triphosphate & 3' C of pervious nucleotide combine to form a phosphodiester bond, a strong covalent bond, releasing pyrophosphate (PPi)
    • Creates sugar-phosphate backbone consisting of alt sugar & phosphate groups with bases projecting sideways
    • 5' ends with phosphate group, 3' ends with free OH group
  5. FORMATION OF DNA DOUBLE HELIX STRUCTURE

    • 2 polynucleotide chains pair up & coil around central axis, forming right-handed double helix
    • Complementary base pairing between purines & pyrimidines:
    • A:T (2 H bonds). G:C (3 H bonds)
    • A:T & C:G = Purine:Pyrimidine = 1:1
  6. All cells of same organism have same amt of DNA (except gametes)
    Alt large major grooves & smaller minor grooves along axis.
    Proteins can interact specifically with exposed atoms in grooves w/o disrupting base pairings.
    • Stability & integrity of double helix maintained by:
    • H bonds between complementary bases
    • Hydrophobic interactions between stacked bases
    • Strong covalent phosphodiester bonds between adj nucleotides
  7. RIBONUCLEIC ACID
    single-stranded
    monomer: ribonucleotide

    Ribose sugar: OH group attached to C2

    • Nitrogenous base: A,G,C,U

    Phosphate group: same as DNA
  8. TYPES OF RNA

    1. mRNA
    • single-stranded, containing info transcribed from DNA
    • Acts as messenger that transfers genetic messages encoded in DNA from nucleus to ribosomes.
    • acts as template for translation (protein sysnthesis)
  9. 2. tRNA
    • specific sequence coded from DNA that allows folding of single RNA strand by forming intramolecular H bonds between complementary bases. (clover leaf structure)
    • Transfers specific amino acids from cytoplasmic pool to ribosome during translation of proteins.
    • Dual recognition sites for involvement in protein synthesis:
    • 1. Amino acid attachment site
    • triplet CCA always at 3' end where enzyme attached amino acid to tRNA
    • 2. Anticodon site
    • composed of 3 nucleotides
    • Each anticodon complementary to corresponding codon on mRNA.
  10. 3. rRNA
    • - component of ribosomes, together with proteins.
    • - 80S ribosomes: 40S small subunit & 60S large subunit
    • - 70S ribosomes: 30S small subunit & 50S large subunit
    • - folds into 3D structure via intermolecular H bonding

    • 1. Acts as an enzyme (ribozyme) providing peptidyl trnasferase activity, catalysing formation of peptide bonds between amino acids
    • 2. Structural role to help orientate ribosomal proteins into correct position within ribosome
    • 3. Large & small subunit interact, aiding in binding of 2 subunits during translation
    • 4. Stabilises interaction between mRNA & tRNA.

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