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

Polissacarídeos como glicogênio e amido são sintetizados a partir de açúcares difosfato de nucleosídeos, como uridina difosfato glicose - UDPG ou adenosina difosfato glicose - ADPG. Ocorre em um fragmento de polímero preexistente, servindo como um primer de alongamento da cadeia. As glicogênio ou amido sintase estendem essas cadeias adicionando unidades de glicose às suas extremidades não redutoras. O UDPG se forma quando a glicose-1-fosfato reage com o trifosfato de uridina, catalisado pela UDP-glicose pirofosforilase. Os açúcares UDP desempenham um papel crucial na biossíntese da parede celular bacteriana. Da mesma forma, o ADPG, sintetizado a partir de glicose-1-fosfato e trifosfato de adenosina via ADP-glicose pirofosforilase, desempenha um papel fundamental na síntese de glicogênio e amido. Além da síntese direta, as células podem gerar glicose por meio da gliconeogênese, utilizando fontes não carboidratos, como lactato, aminoácidos e glicerol. Essa glicose pode ser convertida em UDPG ou ADPG para biossíntese de polissacarídeos. Esses polissacarídeos apoiam a sobrevivência microbiana, contribuindo para a biossíntese da parede celular, armazenamento de carbono e conservação de energia.

biossíntese de polissacarídeos

Biosynthesis of Polysaccharides

Polissacar&#237;deos como o glicog&#234;nio e o amido s&#227;o sintetizados a partir de a&#231;&#250;cares nucleot&#237;deo-difosfato, principalmente uridina difosfato glicose (UDPG) e adenosina difosfato glicose (ADPG). Esses doadores de glicose ativada atuam como intermedi&#225;rios-chave no metabolismo e na bioss&#237;ntese de carboidratos. A UDPG est&#225; envolvida principalmente na s&#237;ntese de glicog&#234;nio em animais e em muitas bact&#233;rias, enquanto a ADPG desempenha um papel fundamental na s&#237;ntese de amido em plantas e em certas bact&#233;rias.
A UDPG &#233; formada quando a glicose-1-fosfato reage com uridina trifosfato (UTP) em uma rea&#231;&#227;o catalisada pela UDP-glicose pirofosforilase. Essa rea&#231;&#227;o gera um doador de glicose de alta energia que participa de diversas vias biossint&#233;ticas. Embora a UDPG contribua para o metabolismo de carboidratos, ela serve como precursor para outros a&#231;&#250;cares UDP, incluindo UDP-N-acetilglicosamina (UDP-GlcNAc) e UDP-N-acetilmur&#226;mico (UDP-MurNAc), essenciais para a bioss&#237;ntese da parede celular bacteriana.
De forma semelhante, a ADPG &#233; sintetizada a partir da glicose-1-fosfato e ATP por meio da ADP-glicose pirofosforilase. Essa enzima &#233; fundamental para a s&#237;ntese de amido em plantas e em certas bact&#233;rias. Uma vez formados, as glicog&#234;nio sintases ou amido sintases adicionam unidades de glicose &#224;s extremidades n&#227;o redutoras das cadeias de polissacar&#237;deos, estendendo seu comprimento.
O Papel da Gliconeog&#234;nese na Ativa&#231;&#227;o de A&#231;&#250;cares
Al&#233;m da s&#237;ntese direta a partir da glicose, as c&#233;lulas podem gerar glicose por meio da gliconeog&#234;nese, utilizando precursores n&#227;o carboidratos como lactato, amino&#225;cidos e glicerol. Esse processo &#233; cr&#237;tico quando h&#225; escassez de fontes externas de glicose. A via reverte a glic&#243;lise, com diferen&#231;as enzim&#225;ticas importantes, permitindo &#224; c&#233;lula produzir glicose a partir de intermedi&#225;rios metab&#243;licos como o fosfoenolpiruvato (PEP). O PEP &#233; sintetizado a partir do oxaloacetato, um intermedi&#225;rio do ciclo do &#225;cido c&#237;trico, e desempenha um papel central no metabolismo microbiano de carboidratos.
A gliconeog&#234;nese compartilha etapas com a glic&#243;lise, mas utiliza enzimas distintas para contornar rea&#231;&#245;es irrevers&#237;veis. Por exemplo, a fosfoenolpiruvato carboxiquinase catalisa a convers&#227;o de oxaloacetato em fosfoenolpiruvato, enquanto a frutose bisfosfatase substitui a fosfofrutoquinase-1 (PFK-1) para conduzir a s&#237;ntese de frutose-6-fosfato. Uma vez que a glicose-6-fosfato &#233; sintetizada pela gliconeog&#234;nese, ela serve como precursora para a&#231;&#250;cares nucleot&#237;deo-difosfato, alimentando a bioss&#237;ntese de polissacar&#237;deos.
Import&#226;ncia Metab&#243;lica dos A&#231;&#250;cares Nucleot&#237;deo-Difosfato
Os a&#231;&#250;cares nucleot&#237;deo-difosfato atuam como doadores de glicose ativados, facilitando a s&#237;ntese de polissacar&#237;deos estruturais e de reserva. A UDPG, por exemplo, &#233; essencial para a s&#237;ntese de glicog&#234;nio e serve como precursor de outros a&#231;&#250;cares UDP, incluindo UDP-galactose e UDP-&#225;cido glucur&#244;nico, os quais s&#227;o fundamentais para a bioss&#237;ntese da parede celular e rea&#231;&#245;es de glicosila&#231;&#227;o. Esses a&#231;&#250;cares funcionam de maneira an&#225;loga ao ATP em rea&#231;&#245;es de fosforila&#231;&#227;o, permitindo a transfer&#234;ncia eficiente de res&#237;duos de glicose nas vias biossint&#233;ticas.
A capacidade das c&#233;lulas de sintetizar polissacar&#237;deos a partir de a&#231;&#250;cares nucleot&#237;deo-difosfato &#233; crucial para a sobreviv&#234;ncia, especialmente em microrganismos que dependem do glicog&#234;nio e do amido como reservas de carbono.

Biossíntese de Polissacarídeos

Polissacar&#237;deos como o glicog&#234;nio e o amido s&#227;o sintetizados a partir de a&#231;&#250;cares nucleot&#237;deo-difosfato, principalmente ...

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Microbiology

Microbiologia

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Microbial Metabolism

Metabolismo Microbiano

KEY TERMS AND CONCEPTS

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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.

microbiology

Activated Sugars for Polysaccharide Synthesis

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