Unity and Diversity in Biochemistry: An Introduction to Chemical Biology

By Marcel Florkin; T. Wood | Go to book overview

CHAPTER I
SOME ASPECTS OF BIOCHEMICAL DIVERSITY

THE chemical processes described in Part Three of this book give an approximate and overall view of the metabolism and biosynthetic mechanisms in cells. However, numerous variations on these themes are possible and a few examples follow.


I. TERPENES

We have described (p. 235) the biosynthesis of isoprene from acetyl-CoA as it usually occurs in cells. In the essential oils of plants we find a large number of compounds which demonstrate the large number of possible compounds which can be formed in a similar manner, starting from acetyl- CoA. They are compounds made up of isopentane units. They contain 5, 10, 15, 20 or more carbon atoms and are called respectively, hemiterpenes, mono-, sesqui-, di- or polyterpenes. From the material which is not distillable in steam, by solvent extraction it is possible to obtain a series of other substances containing 20, 30, 40 carbon atoms or more and belonging to the groups of diterpenes (i.e. the resins), the triterpenes (i.e. the saponins), the tetraterpenes (i.e. the carotenoids) or to the polyterpenes (i.e. rubber). Moreover a whole series of organic compounds synthesized by plants are related to isopentane since they contain such units in their structure. Among these isoprenoids are the irones. There are many monoterpenes in plants and in general, but not always, one can consider their formula as being based on two isopentane units joined in head to tail union. The sesquiterpenes can be considered as formed from three isoprene units in head to tail union. The cyclic monoterpenes and sesquiterpenes can be considered as resulting from the rolling up of the same chains.

Certain of the diterpenes can be considered as containing four isopentane units in head to tail union. This is the case of phytol and vitamin A. Others have an irregular arrangement.

Among the tetraterpenes, those related to lycopene and called carotenoids have been described previously). Plants are able to synthesize carotenoid molecules whilst animals are only able to modify them, for example by oxidation. Astaxanthin a carotenoid usually found in crustaceans, is one such oxidation product.

In mammals, birds, and certain amphibians, the ingestion of carotenoids in the food results in an absorption of carotene in the intestine, the extent of

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Unity and Diversity in Biochemistry: An Introduction to Chemical Biology
Table of contents

Table of contents

  • Title Page iii
  • Contents v
  • List of Abbreviations vii
  • Translator's Preface ix
  • Introduction xi
  • Part One xv
  • Chapter I - The Biosphere 1
  • Chapter II - Constituents of the Biosphere 7
  • References 14
  • References 24
  • References 30
  • References 37
  • References 43
  • References 56
  • Chapter III - Modes of Linkage by Covalent Bonds 57
  • References 60
  • References 62
  • References 77
  • References 82
  • Chapter IV - Macromolecules 83
  • References 85
  • References 93
  • References 107
  • References 111
  • Part Two - Enzymes and Biochemical Energetics 129
  • Chapter I - General Principles of Biochemical Energetics 131
  • References 150
  • Chapter II - Enzymes 151
  • References 176
  • Part Three - Chemical Reactions in the Biosphere 177
  • Introduction 179
  • Chapter I - Destructive and Non-Destructive Methods in Modern Biochemistry 181
  • References 182
  • References 184
  • References 185
  • Chapter II - Priming Reactions 186
  • References 197
  • References 199
  • References 207
  • References 209
  • References 223
  • Chapter III - Biosyntheses 229
  • Part Four - Topobiochemistry and Cellular Regulation 271
  • Chapter I - Cellular Topochemistry 273
  • Conclusions 280
  • References 280
  • Chapter II - Cellular Regulation 282
  • References 286
  • Part Five - Biochemical Diversity 287
  • Chapter I - Some Aspects of Biochemical Diversity 289
  • References 303
  • Chapter II - The Inheritance of Biochemical Characteristics 304
  • References 316
  • Chapter III - Biochemistry and Taxonomy 317
  • References 332
  • Chapter IV - Biochemical Evolution 333
  • References 335
  • References 345
  • Part Six - The Metabolism of the Biosphere 347
  • Introduction 349
  • Chapter I - Entry into the Biosphere 351
  • References 365
  • Chapter II - Departure from the Biosphere 366
  • References 370
  • Chapter III - The Cycles 371
  • References 380
  • Index 381
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