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

I polisaccaridi come il glicogeno e l'amido sono sintetizzati da zuccheri nucleosidici difosfato come uridina difosfato glucosio (UDPG) o adenosina difosfato glucosio (ADPG). Si verifica su un frammento di polimero preesistente, che funge da primer per l'allungamento della catena. Il glicogeno o l'amido sintasi estendono queste catene aggiungendo unità di glucosio alle loro estremità non riducenti. L'UDPG si forma quando il glucosio-1-fosfato reagisce con l'uridina trifosfato, catalizzata dalla UDP-glucosio pirofosforilasi. Gli zuccheri UDP svolgono un ruolo cruciale nella biosintesi della parete cellulare batterica. Allo stesso modo, l'ADPG, sintetizzato dal glucosio-1-fosfato e dall'adenosina trifosfato tramite ADP-glucosio pirofosforilasi, svolge un ruolo chiave nella sintesi del glicogeno e dell'amido. Oltre alla sintesi diretta, le cellule possono generare glucosio attraverso la gluconeogenesi, utilizzando fonti non glucidiche come lattato, aminoacidi e glicerolo. Questo glucosio può essere convertito in UDPG o ADPG per la biosintesi dei polisaccaridi. Questi polisaccaridi supportano la sopravvivenza microbica contribuendo alla biosintesi della parete cellulare, allo stoccaggio del carbonio e al risparmio energetico.

biosintesi dei polisaccaridi

Biosynthesis of Polysaccharides

I polisaccaridi come il glicogeno e l&#8217;amido sono sintetizzati a partire da zuccheri nucleoside difosfato, principalmente uridina difosfato glucosio (UDPG) e adenosina difosfato glucosio (ADPG). Questi donatori attivati di glucosio agiscono come intermedi chiave nel metabolismo e nella biosintesi dei carboidrati. L&#8217;UDPG &#232; coinvolta principalmente nella sintesi del glicogeno negli animali e in molti batteri, mentre l&#8217;ADPG riveste un ruolo fondamentale nella sintesi dell&#8217;amido nelle piante e in alcuni batteri.
L&#8217;UDPG si forma dalla reazione tra il glucosio-1-fosfato e l&#8217;uridina trifosfato (UTP), catalizzata dall&#8217;enzima UDP-glucosio pirofosforilasi. Questa reazione genera un donatore di glucosio ad alta energia che partecipa a numerose vie biosintetiche. Sebbene l&#8217;UDPG contribuisca al metabolismo dei carboidrati, essa funge anche da precursore per altri zuccheri UDP, tra cui UDP-N-acetilglucosamina (UDP-GlcNAc) e UDP-N-acetilmuramico (UDP-MurNAc), essenziali per la biosintesi della parete cellulare batterica.
Analogamente, l&#8217;ADPG &#232; sintetizzata a partire da glucosio-1-fosfato e ATP tramite l&#8217;enzima ADP-glucosio pirofosforilasi. Questo enzima &#232; fondamentale per la sintesi dell&#8217;amido nelle piante e in determinati batteri. Una volta formati, le glicogeno sintasi o le amido sintasi aggiungono unit&#224; di glucosio alle estremit&#224; non riducenti delle catene polisaccaridiche, estendendone la lunghezza.
Il ruolo della gluconeogenesi nell&#8217;attivazione degli zuccheri
Oltre alla sintesi diretta dal glucosio, le cellule possono generare glucosio attraverso la gluconeogenesi, che utilizza precursori non glucidici come il lattato, gli amminoacidi e il glicerolo. Questo processo &#232; cruciale in condizioni di carenza di fonti esogene di glucosio. La via rappresenta una reversibilit&#224; della glicolisi, con differenze enzimatiche chiave, permettendo alla cellula di produrre glucosio da intermedi metabolici come il fosfoenolpiruvato (PEP). Il PEP &#232; sintetizzato a partire da ossalacetato, un intermedio del ciclo dell&#8217;acido citrico, e riveste un ruolo centrale nel metabolismo dei carboidrati nei microrganismi.
La gluconeogenesi condivide delle tappe con la glicolisi ma utilizza diversi enzimi per superare le reazioni irreversibili. Per esempio, la fosfoenolpiruvato carbossichinasi catalizza la conversione dell&#8217;ossalacetato in fosfoenolpiruvato, mentre la fruttosio bisfosfatasi sostituisce la fosfofruttochinasi-1 (PFK-1) per favorire la sintesi del fruttosio-6-fosfato. Una volta sintetizzato il glucosio-6-fosfato tramite la gluconeogenesi, esso funge da precursore per gli zuccheri nucleoside difosfato, alimentando la biosintesi dei polisaccaridi.
Significato metabolico dei nucleoside difosfato costituiti da zuccheri
I nucleosidi difosfato costituiti da zuccheri fungono da donatori attivi di glucosio, facilitando la sintesi di polisaccaridi strutturali e di riserva. L&#8217;UDPG, ad esempio, &#232; essenziale per la sintesi del glicogeno e serve da precursore per altri zuccheri UDP, come l&#8217;UDP-galattosio e l&#8217;UDP-acido glucuronico, che sono fondamentali per la biosintesi della parete cellulare e per le reazioni di glicosilazione. Questi zuccheri funzionano in modo analogo all&#8217;ATP nelle reazioni di fosforilazione, permettendo un efficiente trasferimento dei residui di glucosio nelle vie biosintetiche.
La capacit&#224; delle cellule di sintetizzare polisaccaridi a partire da nucleosidi difosfato costituiti da zuccheri &#232; cruciale per la sopravvivenza, in particolare nei microrganismi che si affidano al glicogeno e all&#8217;amido come riserve di carbonio.

Biosintesi dei polisaccaridi

I polisaccaridi come il glicogeno e l&#8217;amido sono sintetizzati a partire da zuccheri nucleoside difosfato, principalmente uridina difosfato glucosio ...

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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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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.

microbiology

Activated Sugars for Polysaccharide Synthesis

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