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Purines and Pyrimidines

Purines and Pyrimidines. 6. 6. 7. 5. 1. 5. N. N. 1. N. 8. 4. 2. 2. 9. N H. 4. N. N. 3. 3. Purine and Pyrimidine are the names of the parent compounds of two types of nitrogen-containing heterocyclic aromatic compounds. Pyrimidine. Purine. O. O. CH 3. H N. H N. O.

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Purines and Pyrimidines

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  1. Purines and Pyrimidines

  2. 6 6 7 5 1 5 N N 1 N 8 4 2 2 9 N H 4 N N 3 3 • Purineand Pyrimidine are the names of the parent compounds of two types of nitrogen-containing heterocyclic aromatic compounds. Pyrimidine Purine

  3. O O CH3 HN HN O O NH NH Important Pyrimidines • Pyrimidines that occur in DNA: • Cytosine and Thymine. (C & T) • Pyrimidines in RNA: • Cytosine and Uracil. (C & U) NH2 HN O NH Uracil Thymine Cytosine

  4. NH2 O N N HN N NH NH H2N N N Important Purines • Adenine and Guanine are the principal purines of both DNA and RNA. Adenine Guanine

  5. Nucleosides • A nucleoside is a pyrimidine or purine N-glycoside of D-ribofuranose or 2-deoxy-D-ribofuranose. • The purine or pyrimidine part of a nucleoside is referred to as a purine or pyrimidineBase.

  6. NH2 N N O HOCH2 O HO OH Cytidine • Pyrimidine nucleosides Cytidine occurs in RNA; its 2-deoxy analog occurs in DNA

  7. O H3C NH O N HOCH2 O HO Thymidine • Pyrimidine nucleosides Thymidine occurs in DNA

  8. O NH O N HOCH2 O HO OH Uridine • Pyrimidine nucleosides Uridine occurs in RNA

  9. NH2 N N N N HOCH2 O HO OH Adenosine • Purine nucleosides Adenosine occurs in RNA; its 2-deoxy analog occurs in DNA

  10. O N NH N NH2 N HOCH2 O HO OH Guanosine • Purine nucleosides Guanosine occurs in RNA; its 2-deoxy analog occurs in DNA

  11. Nucleotides • Nucleotides are phosphoric acid esters of Nucleosides.

  12. NH2 O N OCH2 HO N P 5' HO N N O 1' 4' 3' 2' HO OH Adenosine 5'-Monophosphate (AMP) • Adenosine 5'-monophosphate (AMP) is also called 5'-adenylic acid.

  13. NH2 N N O O N N OCH2 HO O P P O HO HO HO OH Adenosine Diphosphate (ADP)

  14. NH2 N N O O O N N HO OCH2 P O O P P O HO HO HO HO OH Adenosine Triphosphate (ATP) • ATP is an important molecule in several biochemical processes including:energy storage.

  15. Nucleic Acids • Nucleic acids are polynucleotides.

  16. Nucleic Acids • Nucleic acids first isolated in 1869 (Johann Miescher) • Oswald Avery discovered (1945) that a substance which caused a change in the genetically transmitted characteristics of a bacterium was DNA. • Scientists revised their opinion of the function of DNA and began to suspect it was the major functional component of genes.

  17. Composition of DNA • Erwin Chargaff (Columbia Univ.) studied DNAs from various sources and analyzed the distribution of purines and pyrimidines in them. • The distribution of the bases adenine (A), guanine (G), thymine (T), and cytosine (C) varied among species. • But the total purines (A and G) and the total pyrimidines (T and C) were always equal. • Moreover: %A = %T, and %G = %C

  18. Composition of Human DNA For example: • Adenine (A) 30.3% Thymine (T) 30.3% • Guanine (G) 19.5% Cytosine (C) 19.9% • Total purines: 49.8% Total pyrimidines: 50.1% Purine Pyrimidine

  19. 2-deoxyribose 2-deoxyribose A T Base Pairing • A and T are present in equal amounts in DNA because of complementary hydrogen bonding.

  20. 2-deoxyribose 2-deoxyribose G C Base Pairing • Likewise, the amounts of G and C in DNA were equal because of complementary hydrogen bonding.

  21. The DNA Duplex • A double-stranded structure for DNA in which a purine or pyrimidine base in one chain is hydrogen bonded to its complement in the other. • •Gives proper ratios (A=T and G=C) • •Because each pair contains one purine and one pyrimidine, the A---T and G---C distances between strands are approximately equal.

  22. Two antiparallel strands of DNA are paired by hydrogen bonds between purine and pyrimidine bases.

  23. DNA is coiled • A strand of DNA is too long (about 3 cm in length). • To fit inside a cell, it is coiled. • Efficient coiling of DNA is accomplished with the aid of proteins called histones. • DNA winds around histone proteins to form nucleosomes.

  24. Ribonucleic Acids (RNA)

  25. Three main types of RNA : • 1- Messenger RNA (mRNA): • Transfers DNA code to ribosomes for translation. • 2- Transfer RNA (tRNA): • Brings amino acids to ribosomes for protein synthesis. • 3- Ribosomal RNA (rRNA): • Ribosomes are made of rRNA and protein.

  26. ABDULLATIF TAHA ABDULLAMSc. BIOCHEMISTRY سبحانك لا علم لنا إلا ما علمتنا * إنك أنت العليم الحكيم 0

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