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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
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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.
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Nucleoside = sugar + base
Nucleotide = sugar + base + 1 phosphate group
Nucleoside diphosphate = sugar + base + 2 phosphate groups
Nucleoside triphosphate = sugar + base + 3 phosphate groups
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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
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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
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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
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RIBONUCLEIC ACID
single-stranded
monomer: ribonucleotide
Ribose sugar: OH group attached to C2
- Nitrogenous base: A,G,C,U
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Phosphate group: same as DNA
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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)
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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.
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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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