Nucleotide versus Nucleoside

12 Key excerpts on "Nucleotide versus Nucleoside"

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  eBook - ePub

  Essentials of Organic Chemistry

  For Students of Pharmacy, Medicinal Chemistry and Biological Chemistry

  • Paul M. Dewick(Author)
  • 2013(Publication Date)
  • Wiley

    (Publisher)

  14

  Nucleosides, nucleotides and nucleic acids

  14.1 Nucleosides and nucleotides

  The nucleic acids DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are the molecules that play a fundamental role in the storage of genetic information, and the subsequent manipulation of this information. They are polymers whose building blocks are nucleotides, which are themselves combinations of three parts: a heterocyclic base, a sugar, and phosphate. The most significant difference in the nucleotides comprising DNA and RNA is the sugar unit, which is deoxyribose in DNA and ribose in RNA. The term nucleoside is used to represent a nucleotide lacking the phosphate group, i.e. the base-sugar combination. The general structure of nucleotides and nucleosides is shown below.

  Before we analyse nucleotide structure in detail, it is perhaps best that we consider the nature of the various component parts. In nucleic acid structures, there are five different bases and two different sugars.

  The bases are monocyclic pyrimidines (see Box 11.5 ) or bicyclic purines (see Section 11.9.1), and all are aromatic. The two purine bases are adenine (A) and guanine (G), and the three pyrimidines are cytosine (C), thymine (T) and uracil (U). Uracil is found only in RNA, and thymine is found only in DNA. The other three bases are common to both DNA and RNA. The heterocyclic bases are capable of existing in more than one tautomeric form (see Sections 11.6.2 and 11.9.1). The forms shown here are found to predominate in nucleic acids. Thus, the oxygen substituents are in keto form, and the nitrogen substituents exist as amino groups.

  The two sugars are pentoses, D -ribose in RNA and 2-deoxy-D -ribose in DNA. In all cases, the sugar is present in five-membered acetal ring form, i.e. a furanoside (see Section 12.4). The base is combined with the sugar through an N

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  Molecular Biology

  • David P. Clark(Author)
  • 2009(Publication Date)
  • Academic Cell

    (Publisher)

  adenosine monophosphate, or AMP.

  Table 3.01 Naming Bases, Nucleosides and Nucleotides

  Three-letter abbreviations for the bases such as ade, gua, etc., are sometimes used when writing biochemical pathways or for the names of genes involved in nucleotide metabolism. When writing the sequence of a nucleic acid, the single letter abbreviations are used (A, T, G and C for DNA or A, U, G and C for RNA). The letter N is often used to refer to an unspecified base.

  adenosine	The nucleoside consisting of adenine plus (deoxy)ribose
  deoxynucleoside	A nucleoside containing deoxyribose as the sugar
  deoxynucleotide	A nucleotide containing deoxyribose as the sugar
  nucleoside	The union of a purine or pyrimidine base with a pentose sugar
  nucleotide	Monomer or subunit of a nucleic acid, consisting of a pentose sugar plus a base plus a phosphate group
  ribonucleoside	A nucleoside whose sugar is ribose (not deoxyribose)
  ribonucleotide	A nucleotide whose sugar is ribose (not deoxyribose)

  Double Stranded DNA Forms a Double Helix

  A strand of nucleic acid may be represented in various ways, either in full or abbreviated to illustrate the linkages (Fig. 3.06 ). As remarked above, nucleotides are linked by joining the 5 ′- phosphate of one to the 3 ′-hydroxyl group of the next. Typically, there is a free phosphate group at the 5′-end of the chain and a free hydroxyl group at the 3′-end of a nucleic acid strand. Consequently, a strand of nucleic acid has polarity and it matters in which direction the bases are read off. The 5′-end is regarded as the beginning of a DNA or RNA strand. This is because genetic information is read starting at the 5′-end. [In addition, when genes are replicated, nucleic acids are synthesized starting at the 5′-end as described in Ch. 5

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  Organophosphorus Chemistry

  Volume 44

  • David W Allen, David Loakes, John C Tebby(Authors)
  • 2015(Publication Date)
  • Royal Society of Chemistry

    (Publisher)

  Nucleotides and oligonucleotides: mononucleotides Raman Narukulla a and Yao-Zhong Xu * b DOI: 10.1039/9781782622765-00170 The 60th anniversary of DNA’s discovery marks the conclusion of our first hour of discovery. Each of tick of the year builds on our understanding; to think how differently we viewed things in 1953, and how much progress we have made since then. This chapter is to discuss some selected research work published in the year 2013 on the chemical synthesis of nucleotides and oligonucleotides with an interest in medicinal appli-cations. Due to limited space, it would not be possible to include all relevant articles in it. Nucleotides are the building blocks of nucleic acids which play vital roles in many biological processes. Chemically, a nucleotide is made of a nucleoside (base and sugar) and a phosphate group. Therefore a molecule similar to these compounds could be used as a potential therapeutic agent. Indeed, chemically modified nucleosides and nucleotides have been used for such a purpose. For instance, the first anti-cancer drug methotrexate acted on both thymidylate synthase and on de novo purine synthesis. The importance of these moieties has created great interest and resulted in the formation of a new field of chemistry of nucleic acid components, i.e ., modified nucleotides and oligonucleotides. Relevant research articles on this subject will be discussed in the sections below. 1 Nucleoside monophosphates Nucleoside monophosphates, also called mononucleotides or simply nucleotides, are moieties consisting of one (occasionally two) nucleosides and a single phosphate. They are generally prepared from mono-phosphorylation of nucleosides. 1.1 Modified nucleoside monophosphates There are a limited number of naturally occurring nucleotides, however, synthetic methods are now offering an unlimited number of modified nucleoside monophosphates for biological studies or medicinal exploit-ations.

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  Introduction to Organic Chemistry

  • William H. Brown, Thomas Poon(Authors)
  • 2016(Publication Date)
  • Wiley

    (Publisher)

  Bases are numbered according to the patterns of pyrimidine and purine, the parent compounds. A nucleoside is a compound containing a pentose, either d‐ribose or 2‐deoxy‐d‐ribose bonded to a heterocyclic aromatic amine base by a β‐N‐glycosidic bond (Section 17.4A). Table 20.1 gives the names of the nucleosides derived from the four most common hetero‐ cyclic aromatic amine bases. The monosaccharide component of DNA is 2‐deoxy‐ d‐ribose (the “2‐deoxy” refers to the absence of a hydroxyl group at the 2′ position), whereas that of RNA is d‐ribose. The glycosidic bond is between C‐1′ (the anomeric carbon) of ribose or 2‐deoxyribose and N‐1 of a pyrimidine base or N‐9 of a purine base. Figure 20.2 shows the structural formula for uridine, a nucleoside derived from ribose and uracil. A nucleotide is a nucleoside in which a molecule of phosphoric acid is esterified with a free hydroxyl of the monosaccharide, most commonly either the 3′‐hydroxyl or the 5′‐hydroxyl. A nucleotide is named by giving the name of the parent nucleoside, followed by the word “monophosphate.” The position of the phosphoric ester is speci- fied by the number of the carbon to which it is bonded. Figure 20.3 shows a structural formula and a ball‐and‐stick model of adenosine 5′‐monophosphate. Monophosphoric esters are diprotic acids with pK a values of approximately 1 and 6. Therefore, at a pH Nucleoside A building block of nucleic acids, consisting of D‐ribose or 2‐deoxy‐D‐ribose bonded to a heterocyclic aromatic amine base by a β‐N‐glycosidic bond. Nucleotide A nucleoside in which a molecule of phosphoric acid is esterified with an OH of the monosaccharide, most commonly either the 3′‐OH or the 5′‐OH. H N H CH 2 OH OH OH H H O HN O O a β-N -glycosidic bond β-D-riboside Uridine uracil anomeric carbon 1' 1 2' 2 3 4 5 6 3' 4' 5' FIGURE 20.2 Uridine, a nucleoside. Atom numbers on the monosaccharide rings are primed to distinguish them from atom numbers on the heterocyclic aromatic amine bases.

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  Electrochemistry of Biological Molecules

  • Glenn Dryhurst(Author)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  Purine and Pyrimidine Nucleosides and Nucleotides, Polyribonucleotides, and Nucleic Acids I. INTRODUCTION, NOMENCLATURE, AND STRUCTURE The structure and nomenclature of the purine and pyrimidine nucleosides and nucleotides have been outlined in Chapters 3 and 4, respectively. Polynucleotide is a rather broad term that includes not only nucleic acids, i.e., a nucleic acid is a natural polynucleotide, but also synthetic substances containing only specified nucleotides or a particular sequence of nucleotides. There are two types of nucleic acid. If the sugar associated with the constituent nucleotides is deoxyribose and the pyrimidine bases are cytosine and thymine, the nucleic acid is deoxyribonucleic acid, D N A . If the sugar is ribose and the pyrimidine bases are (mostly) cytosine and uracil, the nucleic acid is ribonucleic acid, R N A . The constituent purine bases in both types of nucleic acid are adenine and guanine. At first sight the sequences of bases in nucleic acids appear to be somewhat random, but in fact the sequence of purine and pyrimidine bases in D N A contains the information for their own replication and for the synthesis of ribosomal, messenger, and transfer R N A molecules. 1 Part of the D N A sequence is copied exactly during synthesis of messenger R N A , except that uracil replaces thymine. Messenger R N A acts as a template for protein synthesis since each three-base sequence in the messenger R N A directs the incorporation of a particular amino acid into a growing peptide chain (protein). As mentioned in earlier chapters, in a similar manner the nucleic acids contain the information for the transfer of genetic information. In double-stranded nucleic acids the amount of adenine always equals the amount of thymine ( D N A ) or uracil ( R N A ) , and the amount of guanine always 269 5 270 5 Purine and Pyrimidine Nucleosides and Nucleotides equals the amount of cytosine.

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  The Molecular Fabric of Cells

  • BIOTOL, B C Currell, R C E Dam-Mieras(Authors)
  • 2013(Publication Date)
  • Butterworth-Heinemann

    (Publisher)

  b) Not a nucleoside! Thymine is just the nitrogenous pyrimidine base, thymine. c) Uridine is the nucleoside compound of uracil and ribose (hence -OH on both C-2' and C-3' of the sugar). 4.4 Nucleotides nucleotide If phosphoric acid (H3 PO4) is esterified to the sugar moiety of a nucleoside, a nucleotide is created. The phosphate is always linked to one of the free hydroxyl groups of the Nucleic acids 79 sugar ie to C-3' or C-5' of ribose. Nucleotides which contain 2-deoxy-D-ribose are called deoxyribonucleotides; those containing D-ribose are known as ribonucleotides. Deoxyribonucleotides are the components of DNA; ribonucleotides are the building blocks of RNA. 4.4.1 Mononucleotides Mononucleotides are named according to the nucleoside which they contain and the position at which the phosphate is attached. Thus a nucleotide containing adenine, ribose and a phosphate linked to the C-5' of ribose becomes AMP adenosine-5'-monophosphate (routinely abbreviated as AMP. The 5' indicates that the phosphate is attached to the C-5' of the sugar). Collectively they are known as nucleoside - monophosphates (NMP). Nucleotides may contain more than one N Dp phosphate group, whereupon they become nucleoside-diphosphates (NDP), if two are present; nucleoside-triphosphates (NTP) when 3 phosphates are present. The NTP arrangements for naming nucleotides are summarised in Figure 4.7. Note that at physiological pH (7-7.5), the hydroxyl groups on the phosphates will, to a large extent, be deprotonated. ATP is thus negatively charged and, in the cytoplasm of cells, is routinely complexed with Mg ++ ions. In enzyme reactions involving ATP, the true substrate is thought to be Mg ++ -ATP. NMP BASE O O O vl ßl cd O -P -O -P -O -P -O -C H ? Ώ II II II | X ° ° ° !fH H-c l ' ' / I H C — C H OH OH I I nucleoside I I nucleoside-5-monophosphate I I nucleoside-5-diphosphate nucleoside-5-triphosphate Figure 4.7 The generalised structure of a nucleoside, and nucleoside-5-mono, di- and triphosphates.

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  Asymmetric Synthesis of Natural Products

  • Ari M. P. Koskinen(Author)
  • 2022(Publication Date)
  • Wiley

    (Publisher)

  Thus, the nucleotides or deoxynucleotides are the actual building blocks of RNA and DNA, respectively. Asymmetric Synthesis of Natural Products, Third Edition. Ari M.P. Koskinen. © 2023 John Wiley & Sons Ltd. Published 2023 by John Wiley & Sons Ltd. 208 Asymmetric Synthesis of Natural Products Table 6.1 Length of genome and number of proteins coded in different eukaryotes. Species M bp Coded proteins Human Homo sapiens 3100 20 000 Rapeseed Brassica napus 125 25 500 Roundworm Chaenorhabditis elegans 97 19 000 Fruit fly Drosphila melanogaster 180 13 600 Baker’s yeast Saccharomyces cerevisiae 12,1 5800 N N NH 2 NH 2 NH 2 N N H N N H N NH O N N H adenine (A) guanine (G) O HN N H O O HN N H O O Me cytosine (C) uracil (U) thymine (T) purines pyrimidines Figure 6.1 Nucleobases O HO OH HO O HO OH HO OH deoxyribose (DNA) ribose (RNA) N N N N O HO HO N N NH 2 NH 2 N N O O O HO deoxyadenosine (dA) deoxynucleoside P – O – O deoxyadenosine monophosphate deoxynucleotide Figure 6.2 DNA and RNA The nucleosides are joined together through phosphodiester linkages between the 5’- and 3’-hydroxyl groups of con- secutive sugars (Figure 6.3). The 2’-hydroxyl group of the RNA can participate as a neighboring group in the hydrolytic cleavage of the adjacent phosphodiester. This intrinsic instability of the RNA polymer is important in preventing RNA from accumulating in the cell. Nucleosides, Nucleotides, and Nucleic Acids 209 N N N N NH 2 NH 2 NH 2 NH 2 NH 2 NH 2 O O P O N O N O O P O O NH N N O N O O P O O NH O O N O O P O O O O P O O O – O – O – O – O – O – O – O – O – O – A adenine C cytosine T thymine G guanine N N N N O O P O N O N O O P O O NH N N O N O O P O O NH O O N O O P O O O O P O O DNA RNA OH OH OH OH U uracil 3' 5' 3' 5' Figure 6.3 DNA and RNA chains The nucleic acids differ in their stability, structure, and function. The three-dimensional structures of DNA and RNA are different, and this is the structural reason for their different functions in cells.

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  Nucleic Acids in Chemistry and Biology

  • G Michael Blackburn, Michael J Gait, David Loakes, David M Williams, Jane A Grasby, Stephen Neidle(Authors)
  • 2015(Publication Date)
  • Royal Society of Chemistry

    (Publisher)

  CHAPTER 3 Nucleosides and Nucleotides

  CONTENTS 3.1    Chemical Synthesis of Nucleosides 3.1.1    Formation of the Glycosylic Bond 3.1.2    Building the Base onto a C-1 Substituent of the Sugar 3.1.3    Synthesis of Acyclonucleosides 3.1.4    Syntheses of Base and Sugar-Modified Nucleosides 3.2    Chemistry of Esters and Anhydrides of Phosphorus Oxyacids 3.2.1    Phosphate Esters 3.2.2    Hydrolysis of Phosphate Esters 3.2.3    Synthesis of Phosphate Diesters and Monoesters 3.3    Nucleoside Esters of Polyphosphates 3.3.1    Structures of Nucleoside Polyphosphates and Co-Enzymes 3.3.2    Synthesis of Nucleoside Polyphosphate Esters 3.4    Biosynthesis of Nucleotides 3.4.1    Biosynthesis of Purine Nucleotides 3.4.2    Biosynthesis of Pyrimidine Nucleotides 3.4.3    Nucleoside Di- and Triphosphates 3.4.4    Deoxyribonucleotides 3.5    Catabolism of Nucleotides 3.6    Polymerisation of Nucleotides 3.6.1    DNA Polymerases 3.6.2    RNA Polymerases 3.7    Therapeutic Applications of Nucleoside Analogues 3.7.1    Anti-Cancer Chemotherapy 3.7.2    Anti-Viral Chemotherapy          References

  3.1 CHEMICAL SYNTHESIS OF NUCLEOSIDES

  The first nucleoside syntheses were planned to prove the structures of adenosine and the other ribo- and Modern syntheses have been aimed at producing nucleoside analogues for using them as inhibitors of nucleic acid metabolism (Section 3.7) and for incorporation into synthetic oligonucleotides (Section 4.4.1). These have a variety of uses such as therapeutic applications using antigene or antisense technologies (Section 5.7.1),1 studying RNA and DNA structure,

  2 ,3

  DNA–protein interactions (Chapter 10) and nucleic acid catalysis (Section 5.7.3). In spite of advances in stereospecific synthesis, it remains more economical to produce the major nucleosides by degrading nucleic acids than by total synthesis.

  Modified nucleosides are widely distributed naturally. For example, all species of tRNA contain unusual minor bases and many bacteria and fungi provide rich sources of nucleosides modified in the base, in the sugar or in both base and sugar residues. Since some of these have been found to show a wide and useful range of biological activity, thousands of nucleoside analogues have been synthesised in pharmaceutical laboratories across the world. In recent times, industrial targets for this work have been anti-viral and anticancer agents. For instance, the arabinose analogues of adenosine and cytidine, ara A and ara C, are useful as anti-viral and anti-leukaemia drugs, while 5-iodouridine is valuable for treating Herpes simplex infections of the eye (Figure 3.1

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  Applications

  • Z. Deyl(Author)
  • 2000(Publication Date)
  • Elsevier Science

    (Publisher)

  341 Chapter 14 NUCLEOTIDES, NUCLEOSIDES, NITROGENOUS CONSTITUENTS OF NUCLEIC A C I D S s. ZADRA~IL GENERAL ASPECTS Heterocyclic nitrogenous bases derived from purines and pyrimidines - adenine, guanine o r cytosine, u r a c i l and thymine, and t h e corresponding nucleosides and nucleotides - a r e t h e only, though decisive, c e l l c o n s t i t u e n t s i n l i v i n g organisms bound t o n u c l e i c acids. I n a d d i t i o n t h e r e a r e t h e i r polyphosphate d e r i v a t i v e s (immediate precursors o f n u c l e i c a c i d biosynthesis and n a t u r a l sources o f energy) 01 igonucleotides and modified nucleosides (mostly methylated d e r i v a t i v e s a r i s i n g 4 a t the l e v e l o f macromolecules) c a t a b o l i c processes o f nucleic acids i n t h e c e l l , o r nucleotide coenzymes and a n t i b i o t i c s d e r i v a t i v e s and analogues of t h e n u c l e i c a c i d constituents r e s u l t from i n v i t r o synthetic a c t i v i t y i n organic chemistry l a b o r a t o r i e s where, i n a d d i t i o n t o t h e i n c r e a s i n g l y used nucleotides and 01 igonucleotides6, i n biochemistry and mole- c u l a r b i o l o g y ( s y n t h e t i c l i n k e r s , primers, genes and t h e i r p o r t i o n s ) t h e number o f analogues and antimetabol i t e s 7 , which have been synthesized, t e s t e d and used as p o t e n t i a l and r e a l v i r o s t a t i c s , b a c t e r i o s t a t i c s , c y t o s t a t i c s , c a r c i n o s t a t i c s o r o t h e r therapeutics i s extended.

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  Engström-Finean Biological Ultrastructure

  • J. B. Finean(Author)
  • 2013(Publication Date)
  • Academic Press

    (Publisher)

  C H A P T E R V Role of Nucleic Acids Although proteins may be the foundation stones of biological ultra-structure they owe their design and construction to the nucleic acids which are the ultimate source of the codes of life. Nucleic acids were identified by Miescher in 1871, but it was not until about 1930 that they began to attract any scientific attention. Developments of recent years have been spectacular, and the story of the form in which these mole-cules hold their secrets and of how they perpetuate them and apply them in the construction and maintenance of living systems provides one of the most fascinating chapters of molecular biology. A. The Structure of Nucleic Acids and Nucleoproteins The nucleic acids are polymers of the general form ^ I Base—Sugar—Phosphate I Base—Sugar—Phosphate Nucleotide The monomer (nucleotide) consists of a base, a sugar, and a phosphate. 1. THE SUGAR COMPONENT In practically all nucleic acids analyzed thus far, the sugar component has been found to be either D-ribose or 2-deoxy-D-ribose (Fig. V.l) and this has led to the differentiation of two main types of nucleic acid, ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). From some points of view it may be preferable to use the generic terms pentose nucleic acid (PNA) and deoxypentose nucleic acid (DNA). 193 194 V. Role of Nucleic Acids CH 2 OH OH OH OH H (a) (b) FIG. V.l. Structural formulas of (a) D-ribose and (b) 2-deoxy-r>ribose. 2. THE HETEROCYCLIC BASES, PURINES AND PYRIMIDINES The structural formulas of four of the main purines and pyrimidines found in nucleic acids are given in Fig. V.2. Crystallographic studies of these molecules in isolation have indicated that the ring structures are approximately planar and that there are small variations in the C—N and C—C bond lengths associated with differences in the double bond character arising in particular from the keto and amido groups attached to the rings.

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  Organic and Biological Chemistry

  • H. Stephen Stoker(Author)
  • 2015(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 502-b CHAPTER 11 Nucleic Acids 11-24 What nitrogen-containing base and what sugar are pres-ent in each of the following nucleotides? a. GMP b. dAMP c. CMP d. dCMP 11-25 What is the name of each of the nucleotides in Problem 11-23? 11-26 What is the name of each of the nucleotides in Problem 11-24? 11-27 Consider the following nucleotide. O O A P O 2 O P O 2 A CH 2 N O O N H O CH 3 O H OH a. What is the name of the nucleotide? b. Would this nucleotide be found in both DNA and RNA, only in DNA, or only in RNA? c. What is the name for the type of bond that connects the phosphate and sugar subunits? d. What is the name for the type of bond that connects the sugar and base subunits? 11-28 Consider the following nucleotide. O O OH CH 2 O N H N O NH 2 N N OH A P O 2 P O 2 A O O a. What is the name of the nucleotide? b. Would this nucleotide be found in both DNA and RNA, only in DNA, or only in RNA? c. What is the name for the type of bond that connects the phosphate and sugar subunits? d. What is the name for the type of bond that connects the sugar and base subunits? ▲ 11-29 Indicate whether each of the following is (1) a nucleoside, (2) a nucleotide, or (3) neither a nucleoside nor a nucleotide. a. Adenosine b. Adenine c. dAMP d. Adenosine 5 ′ -monophosphate ▲ 11-30 Indicate whether each of the following is (1) a nucleoside, (2) a nucleotide, or (3) neither a nucleoside nor a nucleotide. a. Cytosine b. Cytidine c. CMP d. Deoxycytidine 5 ′ -monophosphate Primary Nucleic Acid Structure (Section 11-4) 11-31 For the trinucleotide 5 ′ G – C – A 3 ′ a. How many nucleotide subunits are present in its “backbone”? b.

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  Carbohydrates

  • J. B. Harborne(Author)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  Nucleotide sugars were isolated from a large variety of organisms, both prokaryotic and eukary- otic, and their biosynthesis was explored in detail. Their function as donors of carbo- hydrate moieties in the biosynthesis of oligosaccharides, polysaccharides, proteo- glycans, glycolipids, and a large variety of simple and complex glycosides of plants, has now been amply demonstrated. The high water-mark of nucleotide sugar research was reached in the late 1970s, and the number of new publications concerned with these compounds has been constantly decreasing. Since they are connected with such a large variety of metabolic processes, nucleotide sugars have now become common laboratory reagents and are used almost daily in many investigations. Nonetheless, in the realm of plant biochemistry some intriguing unsolved problems involving nucleotide sugars remain. Perhaps the most interesting and enigmatic of these is the biosynthesis of the L-arabinofuranosyl moiety. This structure is widely distributed among plant poly- saccharides, yet its mode of formation remains a complete mystery. Another problem of considerable significance, at least quantitatively, concerns the synthesis of cellulose and other polysaccharides of the plant cell wall. These are all presumably derived from nucleotide sugar precursors, but the details of the overall processes are still surprisingly obscure. Attempts to solve these and similar problems will doubtless occupy plant biochemists and physiologists for some time to come. III. SUMMARY OF THE BIOSYNTHESIS OF NUCLEOTIDE SUGARS IN HIGHER PLANTS Current knowledge of the biosynthesis of sugar nucleotides in higher plants is summar- ised in Fig. 2.1. Many of the compounds and reactions depicted have been demon- strated in other organisms, both prokaryotic and eukaryotic. Some reactions, like the sucrose biosynthesis and utilisation sequences, are found uniquely in plants.

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