Name: activated sugars for polysaccharide synthesis
Uploaded: 2025-06-12T09:37:21.000Z
Duration: 1 min 26 s
Channel: JoVE

Les polysaccharides comme le glycogène et l’amidon sont synthétisés à partir de sucres nucléosidiques diphosphates tels que l’uridine diphosphate glucose (UDPG) ou l’adénosine diphosphate glucose (ADPG). Il se produit sur un fragment de polymère préexistant, servant d’amorce d’allongement de chaîne. Les glycogènes ou les synthases d’amidon étendent ces chaînes en ajoutant des unités de glucose à leurs extrémités non réductrices. L’UDPG se forme lorsque le glucose-1-phosphate réagit avec l’uridine triphosphate, catalysé par l’UDP-glucose pyrophosphorylase. Les sucres UDP jouent un rôle crucial dans la biosynthèse de la paroi cellulaire bactérienne. De même, l’ADPG, synthétisé à partir du glucose-1-phosphate et de l’adénosine triphosphate via l’ADP-glucose pyrophosphorylase, joue un rôle clé dans la synthèse du glycogène et de l’amidon. Au-delà de la synthèse directe, les cellules peuvent générer du glucose par gluconéogenèse, en utilisant des sources non glucidiques telles que le lactate, les acides aminés et le glycérol. Ce glucose peut être converti en UDPG ou ADPG pour la biosynthèse des polysaccharides. Ces polysaccharides favorisent la survie microbienne en contribuant à la biosynthèse de la paroi cellulaire, au stockage du carbone et à la conservation de l’énergie.

biosynthèse des polysaccharides

Biosynthesis of Polysaccharides

Les polysaccharides tels que le glycog&#232;ne et l&#8217;amidon sont synth&#233;tis&#233;s &#224; partir de sucres nucl&#233;oside-diphosphate, principalement l&#8217;uridine diphosphate glucose (UDPG) et l&#8217;ad&#233;nosine diphosphate glucose (ADPG). Ces donneurs de glucose activ&#233;s jouent un r&#244;le cl&#233; dans le m&#233;tabolisme et la biosynth&#232;se des glucides. L&#8217;UDPG est principalement impliqu&#233; dans la synth&#232;se du glycog&#232;ne chez les animaux et de nombreuses bact&#233;ries, tandis que l&#8217;ADPG est fondamental dans la synth&#232;se de l&#8217;amidon chez les plantes et certaines bact&#233;ries.
L&#8217;UDPG est form&#233;e lorsque le glucose-1-phosphate r&#233;agit avec l&#8217;uridine triphosphate (UTP), dans une r&#233;action catalys&#233;e par l&#8217;UDP-glucose pyrophosphorylase. Cette r&#233;action g&#233;n&#232;re un donneur de glucose &#224; haute &#233;nergie qui intervient dans de nombreuses voies biosynth&#233;tiques. Bien que l&#8217;UDPG contribue au m&#233;tabolisme des glucides, elle sert &#233;galement de pr&#233;curseur &#224; d&#8217;autres sucres UDP, notamment l&#8217;UDP-N-ac&#233;tylglucosamine (UDP-GlcNAc) et l&#8217;UDP-N-ac&#233;tylmuramique (UDP-MurNAc), essentiels &#224; la biosynth&#232;se de la paroi cellulaire bact&#233;rienne.
De mani&#232;re similaire, l&#8217;ADPG est synth&#233;tis&#233;e &#224; partir de glucose-1-phosphate et d&#8217;ATP par l&#8217;ADP-glucose pyrophosphorylase. Cette enzyme est fondamentale pour la synth&#232;se de l&#8217;amidon chez les plantes et certaines bact&#233;ries. Une fois form&#233;, le glycog&#232;ne ou l&#8217;amidon est allong&#233; par l&#8217;ajout d&#8217;unit&#233;s de glucose aux extr&#233;mit&#233;s non r&#233;ductrices des cha&#238;nes polysaccharidiques, via des glycog&#232;ne ou amidon synthases.
R&#244;le de la n&#233;oglucogen&#232;se dans l&#8217;activation des sucres
En plus de la synth&#232;se directe &#224; partir du glucose, les cellules peuvent produire du glucose par n&#233;oglucogen&#232;se, en utilisant des pr&#233;curseurs non glucidiques tels que le lactate, les acides amin&#233;s et le glyc&#233;rol. Ce processus est crucial lorsque les sources externes de glucose sont limit&#233;es. La voie inverse la glycolyse, avec des diff&#233;rences enzymatiques cl&#233;s, permettant &#224; la cellule de produire du glucose &#224; partir d&#8217;interm&#233;diaires m&#233;taboliques comme le phospho&#233;nolpyruvate (PEP). Le PEP est synth&#233;tis&#233; &#224; partir de l&#8217;oxaloac&#233;tate, un interm&#233;diaire du cycle de l&#8217;acide citrique, et joue un r&#244;le central dans le m&#233;tabolisme glucidique microbien.
La n&#233;oglucogen&#232;se partage plusieurs &#233;tapes avec la glycolyse mais utilise des enzymes distinctes pour contourner les r&#233;actions irr&#233;versibles. Par exemple, la phospho&#233;nolpyruvate carboxykinase catalyse la conversion de l&#8217;oxaloac&#233;tate en phospho&#233;nolpyruvate, tandis que la fructose bisphosphatase remplace la phosphofructokinase-1 (PFK-1) pour g&#233;n&#233;rer du fructose-6-phosphate. Une fois le glucose-6-phosphate synth&#233;tis&#233; par n&#233;oglucogen&#232;se, il sert de pr&#233;curseur aux sucres nucl&#233;oside-diphosphate, alimentant la biosynth&#232;se des polysaccharides.
Importance m&#233;tabolique des sucres nucl&#233;oside-diphosphate
Les sucres nucl&#233;oside-diphosphate agissent comme des donneurs de glucose activ&#233;s, facilitant la synth&#232;se des polysaccharides de structure et de r&#233;serve. L&#8217;UDPG, par exemple, est essentielle &#224; la synth&#232;se du glycog&#232;ne et sert de pr&#233;curseur &#224; d&#8217;autres sucres UDP, tels que l&#8217;UDP-galactose et l&#8217;UDP-glucuronique, qui sont indispensables &#224; la biosynth&#232;se de la paroi cellulaire et aux r&#233;actions de glycosylation. Ces sucres remplissent une fonction analogue &#224; celle de l&#8217;ATP dans les r&#233;actions de phosphorylation, permettant le transfert efficace de r&#233;sidus de glucose dans les voies biosynth&#233;tiques.
La capacit&#233; des cellules &#224; synth&#233;tiser des polysaccharides &#224; partir de sucres nucl&#233;oside-diphosphate est cruciale pour la survie, en particulier chez les micro-organismes qui d&#233;pendent du glycog&#232;ne et de l&#8217;amidon comme r&#233;serves de carbone.

Biosynthèse des polysaccharides

Les polysaccharides tels que le glycog&#232;ne et l&#8217;amidon sont synth&#233;tis&#233;s &#224; partir de sucres nucl&#233;oside-diphosphate, ...

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activated sugars for polysaccharide synthesis

Activated sugars drive polysaccharide synthesis in cells. Glycogen and starch are built from nucleoside diphosphate sugars, mainly uridine diphosphate glucose (UDPG) and adenosine diphosphate glucose (ADPG). These sugar donors act as high-energy intermediates in carbohydrate metabolism and biosynthesis.

UDPG supports glycogen synthesis in animals and many bacteria. It forms when glucose-1-phosphate reacts with uridine triphosphate (UTP). UDP-glucose pyrophosphorylase catalyzes this reaction. UDPG also serves as a precursor for other UDP sugars, including UDP-N-acetylglucosamine (UDP-GlcNAc) and UDP-N-acetylmuramic acid (UDP-MurNAc). These molecules are important for bacterial cell wall biosynthesis.

ADPG has a key role in starch synthesis in plants and some bacteria. It is made from glucose-1-phosphate and ATP by ADP-glucose pyrophosphorylase. After ADPG is formed, glycogen synthases or starch synthases add glucose units to the non-reducing ends of polysaccharide chains. This extends the chain.

Cells can also make glucose through gluconeogenesis when outside glucose is low. Gluconeogenesis uses non-carbohydrate sources such as lactate, amino acids, and glycerol. The pathway runs in reverse direction from glycolysis, but it uses different enzymes to bypass irreversible steps. Phosphoenolpyruvate carboxykinase converts oxaloacetate to phosphoenolpyruvate, and fructose bisphosphatase replaces phosphofructokinase-1 to help form fructose-6-phosphate.

Gluconeogenesis connects to polysaccharide synthesis after glucose-6-phosphate is made. That compound can be turned into nucleoside diphosphate sugars and then used to build storage and structural polysaccharides. In microbial metabolism, phosphoenolpyruvate made from oxaloacetate is an important part of this process.

Nucleoside diphosphate sugars act like activated glucose donors, much like ATP helps drive phosphorylation reactions. UDPG is important not only for glycogen synthesis, but also as a source of UDP-galactose and UDP-glucuronic acid. These sugars support cell wall biosynthesis and glycosylation reactions. This ability to make polysaccharides helps cells survive, especially microorganisms that use glycogen and starch as carbon reserves.

Activated Sugars for Polysaccharide Synthesis

activated-sugars-for-polysaccharide-synthesis

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Activated sugars drive polysaccharide synthesis in cells. Glycogen and starch are built from nucleoside diphosphate sugars, mainly uridine diphosphate glucose (UDPG) and adenosine diphosphate glucose (ADPG). These sugar donors act as high-energy intermediates in carbohydrate metabolism and biosynthesis. UDPG supports glycogen synthesis in animals and many bacteria. It forms when glucose-1-phosphate reacts with uridine triphosphate (UTP). UDP-glucose pyrophosphorylase catalyzes this reaction.

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key terms and concepts

Learn how UDPG and ADPG activate glucose for glycogen and starch synthesis, and how gluconeogenesis supplies precursors for polysaccharide production.

Activated Sugars for Polysaccharide Synthesis | JoVE K12

JoVE Core Microbiology provides an engaging introduction to the microbial world and its influence on health, industry, and the environment. This comprehensive collection covers key concepts such as microbial structure, metabolism, genetics, and ecology. It introduces essential laboratory techniques and microscopy methods through visually engaging animations. Corresponding scientist-in-action videos bridge classroom concepts with real-world research and applications.

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Activated Sugars for Polysaccharide Synthesis

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