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Nucleic Acid Chemistry BIOMEDICAL IMPORTANCE They form a part of many coenzymes. Serve as donors of phosphoryl groups (eg, ATP or GTP) Regulatory nucleotides include the second messengers cAMP and cGMP Synthetic purine and pyrimidine analogs that contain halogens, thiols, or additional nitrogen are employed for chemotherapy of cancer and AIDS BIOMEDICAL IMPORTANCE Suppressors of the immune response during organ transplantation. Genetic diseases of purine metabolism include gout There are few clinically significant disorders of pyrimidine catabolism Nucleic acid DNA or RNA Adenine A DNA or RNA Guanine G DNA or RNA Uracil U RNA only Cytosine C DNA or RNA Thymine T DNA Nucleic acid ↓ Nuclease Nucleotides ↓ Nucleotidase Nucleoside + Phosphoric acid (H3PO4) ↓ Nucleosidase Pentose + Nitrogenous base ↓ ↓ Ribose or Deoxyribose RNA DNA Purines Pyrimidines A, G U, C, T Nitrogenous bases Image from: https://sp2.yimg.com/ib/th?id=HN.608002206304175330&pid=15.1 Nucleosides SUGAR (Pentose) + Nitrogenous Base Nucleotides SUGAR (Pentose) + Nitrogenous Base + Phosphate They are formed by esterification of phosphoric acid to the OH of C5` of Pentose sugar of the nucleoside. Nucleic acid structure Image from: https://sp2.yimg.com/ib/th?id=HN.607999655087770354&pid=15.1 The Polynucleotide structure of nucleic acids is obtained by esterification of phosphate of each nucleotide with the OH group of the C3` of pentose of the adjacent nucleotide. The nucleic acid has 2 ends: The 5 ` end: has a `5 (P) group. The `3 end: has a `3 free (OH) group. Human DNA Human DNA is composed of TWO POLYNUCLEOTIDE STRANDS. DNA PRIMARY STRUCTURE PENTOSE SUGAR: 2-deoxyribose N BASES: A, G, C and T NUCLEOTIDES: dAMP, dGMP, dCMP, dTMP DNA PRIMARY STRUCTURE Sugar and Phosphate form backbone structure (OUTSIDE) Nitorgenous bases (INSIDE) 3` --free OH group of pentose sugar. 5` --free phosphate group Sequence is written from 5 ` → 3 ` direction. DNA secondary structure 2 helices, opposite Backbone (P & S) Outside N Bases (inside) 3.4 Å 10 base (34 Å) 20 Å diameter Image from: http://www.all-about-forensic-science.com/images/dna-pictures8.jpg DNA secondary structure Watson-Crick model of DNA 1. Two helical polynucleotide chains are coiled around a common axis. (DOUBLE HELIX) 2. The chains run in opposite directions. (ANTIPARALLEL) 3. The sugar-phosphate backbones are on the OUTSIDE. 4. The purine and pyrimidine bases lie on the INSIDE of the helix. Complementary Bases A = T - G=C Watson-Crick model of DNA 5. The bases are nearly perpendicular to the helix axis 6. Adjacent bases are separated by 3.4 Å. 7. The helical structure repeats every 34 Å, so there are 10 bases (34 Å per repeat/3.4 Å per base) per turn of helix. 8. The diameter of the helix is 20 Å. https://sp2.yimg.com/ib/th?id=HN.608027112814809070&pid=15.1 DNA Site: Nucleus Mitochondria Functions: Carry genetic informations RNA synthesis Nucleotides Are polyfunctional Acids Free purine or pyrimidine bases are uncharged at physiologic pH Phosphoryl groups of nucleotides ensure that they bear a negative charge at physiologic pH nucleotides absorb light at a wavelength close to 260 nm The concentration of nucleotides and nucleic acids thus often is expressed in terms of “ABSORBANCE AT 260 nm.” Human RNA Site: Mainly in the cytosol, less common in the nucleus. Sugar: Ribose Bases: A, G, C and U. Nucleotides: AMP, GMP, CMP and UMP. RNA (Ribonucleic Acid) Ribosomal RNA (rRNA) constituents of ribosomes, the intricate cellular machines that synthesize proteins. Messenger RNA (mRNA) encode the amino acid sequence of one or more specified by a gene. Transfere RNA (tRNA) read the information encoded in the mRNA and transfer the appropriate amino acid to a growing polypeptide chain during protein synthesis. Ribosomal RNA (rRNA) Its about 80% of total RNA. Function, Synthesis of 2 ribosomal subunits. RIBOSOSMES: Formed of ribonucleoproteins (rRNA + protein) 2 subunits Small (40S) and Large (60S) 40S + 60S form 80S ribosome, responsible of Protein synthesis. Messenger RNA (mRNA) Its about 5% of the total RNA. Carry the message, genetic information from DNA to protein.. Each 3 bases in the mRNA code for one amino acid (CODON) Genetic code. AUG codes for methionine UCA codes for serine Transfere RNA (tRNA) Its about 15% of the total RNA. Carry and transport amino acids to ribosomes. (PROTEIN SYNTHESIS). Each tRNA is compsed of 70 - 90 nts. Clover leaf shape (3 lops and small lump). More than 20 different types of tRNA. ONE ON ONE. (aa : tRNA) Amino acid + tRAN = amino acyle tRNA. https://sp.yimg.com/ib/th?id=HN.608037876000360084&pid=15.1 Image from: http://www.biology.iupui.edu/biocourses/N100/images/13translation.gif DNA Site RNA Cytosol Shape Nucleus & mitochondria Double helix Strand Double stranded Single stramded Purines A, G A, G Pyrimidines C, T C, U Types One Three Functions Carry genetic information, RNA synthesis Protein synthesis Variable