TAILIEUCHUNG - Ebook Harper’s illustrated biochemistry (26th edition): Part 12

(BQ) Part 2 book "Harper’s illustrated biochemistry" presents the following contents: Structure, function and replication of informational macromolecules; biochemistry of extracellular and intracellular communication, special topics. | SECTION IV Structure Function Replication of Informational Macromolecules Nucleotides 33 Victor W. Rodwell PhD BIOMEDICAL IMPORTANCE Nucleotides the monomer units or building blocks of nucleic acids serve multiple additional functions. They form a part of many coenzymes and serve as donors of phosphoryl groups eg ATP or GTP of sugars eg UDP- or GDP-sugars or of lipid eg CDP-acylglyc-erol . Regulatory nucleotides include the second messengers cAMP and cGMP the control by ADP of oxidative phosphorylation and allosteric regulation of enzyme activity by ATP AMP and CTP. Synthetic purine and pyrimidine analogs that contain halogens thiols or additional nitrogen are employed for chemotherapy of cancer and AIDS and as suppressors of the immune response during organ transplantation. PURINES PYRIMIDINES NUCLEOSIDES NUCLEOTIDES Purines and pyrimidines are nitrogen-containing heterocycles cyclic compounds whose rings contain both carbon and other elements hetero atoms . Note that the smaller pyrimidine has the longer name and the larger purine the shorter name and that their six-atom rings are numbered in opposite directions Figure 33-1 . The planar character of purines and pyrimidines facilitates their close association or stacking which stabilizes double-stranded DNA Chapter 36 . The oxo and amino groups of purines and pyrimidines exhibit keto-enol and amine-imine tautomerism Figure 33-2 but physiologic conditions strongly favor the amino and oxo forms. H A 1 .JC. C H N 4 N9 3 H Purine 7 N CH H a Cs 3N Ch HC .QH 2 N 6 1 Pyrimidine Figure 33-1. Purine and pyrimidine. The atoms are numbered according to the international system. Nucleosides Nucleotides Nucleosides are derivatives of purines and pyrimidines that have a sugar linked to a ring nitrogen. Numerals with a prime eg 2 or 39 distinguish atoms of the sugar from those of the heterocyclic base. The sugar in ribonucleosides is D-ribose and in deoxyribonucleosides it is 2-deoxy-D-ribose. The sugar is linked to the .

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• Special topics
• Harper’s illustrated biochemistry
• Replication of informational macromolecules
• Biochemistry of extracellular
• Intracellular communication
• Illustrated biochemistry
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