1. Purines and Pyrimidines4

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

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

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

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

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

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

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

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

11. Nucleotides
Nucleotides are phosphoric acid esters of Nucleosides. 4

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

13. Adenosine Diphosphate (ADP)
OCH2 OH N
NH2

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

15. Nucleic acids are polynucleotides.4

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:
Purine
Pyrimidine
Adenine (A) 30.3% Thymine (T) 30.3% Guanine (G) 19.5% Cytosine (C) 19.9% Total purines: 49.8% Total pyrimidines: 50.1%

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

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

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)4

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 ABDULLA MSc. BIOCHEMISTRY
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