Name: building the bacterial cell wall
Uploaded: 2025-06-12T09:29:31.000Z
Duration: 1 min 28 s
Channel: JoVE

K12 Standards

Virginia  Standards of Learning

HIgh School

Biology

BIO.4

BIO.4.c

Peptidoglycan Synthesis

O peptidoglicano, um componente chave da parede celular bacteriana, é feito de unidades alternadas de N-acetilglucosamina, ou NAG, e ácido N-acetilmurâmico ou NAM unidas por ligações glicosídicas β-1,4. A síntese de peptidoglicano envolve três fases. No citoplasma, as moléculas de difosfato de uridina (UDP) estão covalentemente ligadas ao NAG. O UDP-NAG é convertido enzimaticamente em UDP-NAM. Em seguida, uma cadeia pentapeptídica é adicionada ao UDP-NAM para formar um pentapeptídeo UDP-NAM. Na fase associada à membrana, o NAM-pentapeptídeo está ligado ao fosfato de bactoprenol, formando lipídio I no lado citoplasmático da membrana plasmática. A adição de uma unidade NAG ao Lipídio I forma o Lipídio II, que é translocado através da membrana para o periplasma por uma flippase. Na fase periplasmática, as glicosiltransferases formam ligações glicosídicas para adicionar o pentapeptídeo NAG-NAM-à cadeia peptidoglicana em crescimento ligada ao bactoprenol. Na etapa final, a enzima transpeptidase forma ligações cruzadas de peptídeos entre as cadeias de glicanos, libera a cadeia do bactoprenol e completa a síntese ligando os peptídeos do tronco.

síntese de peptidoglicano

Estrutura do Peptidoglicano
O peptidoglicano &#233; um componente estrutural vital da parede celular bacteriana, conferindo resist&#234;ncia mec&#226;nica e forma &#224; c&#233;lula. Ele &#233; composto por unidades repetidas de dois a&#231;&#250;cares&#8212;N-acetilglicosamina (NAG) e N-acetilmur&#226;mico (NAM)&#8212;ligados por liga&#231;&#245;es glicos&#237;dicas &#946;-1,4. Essas cadeias de a&#231;&#250;cares s&#227;o entrecruzadas por cadeias pept&#237;dicas curtas, formando um pol&#237;mero em forma de malha que envolve a membrana plasm&#225;tica bacteriana.
Fase Citoplasm&#225;tica &#8211; S&#237;ntese de Precursores
A bioss&#237;ntese do peptidoglicano inicia-se no citoplasma com a forma&#231;&#227;o de precursores sol&#250;veis. Nesta etapa, o difosfato de uridina (UDP), um &#233;ster do &#225;cido pirofosf&#243;rico, liga-se a NAG e NAM para formar UDP-NAG e UDP-NAM, respectivamente. O UDP-NAG &#233; ent&#227;o convertido enzimaticamente em UDP-NAM. Uma cadeia pentapept&#237;dica&#8212;tipicamente composta por L-alanina, &#225;cido D-glut&#226;mico, &#225;cido meso-diaminopim&#233;lico (ou L-lisina) e dois res&#237;duos de D-alanina&#8212;&#233; adicionada sequencialmente ao UDP-NAM, formando UDP-NAM-pentapept&#237;deo. Este composto serve como unidade estrutural fundamental para as etapas subsequentes da s&#237;ntese do peptidoglicano.
Fase Associada &#224; Membrana &#8211; Transfer&#234;ncia por Carreador Lip&#237;dico
Na fase associada &#224; membrana, o UDP-NAM-pentapept&#237;deo &#233; transferido para o bactoprenol-fosfato, um carreador lip&#237;dico embutido no folheto interno da membrana plasm&#225;tica. Essa transfer&#234;ncia resulta na forma&#231;&#227;o do Lip&#237;deo I. Em seguida, uma unidade de NAG &#233; adicionada ao Lip&#237;deo I, gerando o Lip&#237;deo II, que agora cont&#233;m a estrutura completa de dissacar&#237;deo-pentapept&#237;deo. Uma enzima flippase ent&#227;o transloca o Lip&#237;deo II atrav&#233;s da membrana, entregando o precursor ao lado peripl&#225;smico para incorpora&#231;&#227;o na parede celular em crescimento.
Fase Peripl&#225;smica &#8211; Polimeriza&#231;&#227;o e Liga&#231;&#245;es Cruzadas
Na fase final, localizada no periplasma, as glicosiltransferases incorporam as unidades de dissacar&#237;deo-pentapept&#237;deo &#224; malha de peptidoglicano existente por meio da cat&#225;lise da forma&#231;&#227;o de liga&#231;&#245;es glicos&#237;dicas. A &#250;ltima etapa, conhecida como transpeptida&#231;&#227;o, &#233; realizada por enzimas transpeptidases. Essa rea&#231;&#227;o libera a subunidade do bactoprenol e forma liga&#231;&#245;es pept&#237;dicas cruzadas entre os pept&#237;deos troncais adjacentes, refor&#231;ando a integridade estrutural da camada de peptidoglicano e completando o processo de bioss&#237;ntese.

Síntese de Peptidoglicano

Estrutura do Peptidoglicano
O peptidoglicano &#233; um componente estrutural vital da parede celular bacteriana, conferindo resist&#234;ncia mec&#226;nica ...

Education

JoVE Core

Microbiology

Microbiologia

Unit

Unidade

Microbial Cell Structure and Function        

Estrutura e Função da Célula Microbiana

KEY TERMS AND CONCEPTS

TERMOS E CONCEITOS-CHAVE

building the bacterial cell wall

Peptidoglycan builds the bacterial cell wall and gives the cell its shape and strength. It is a mesh-like polymer around the bacterial plasma membrane. The polymer is made of repeating sugar units, N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM), linked by β-1,4 glycosidic bonds. Short peptide chains cross-link the sugar chains and make the wall more rigid.

Peptidoglycan biosynthesis starts in the cytoplasm with soluble precursors. Uridine diphosphate, or UDP, binds to NAG and NAM to form UDP-NAG and UDP-NAM. UDP-NAG is then converted into UDP-NAM by enzymes. A pentapeptide chain is added step by step to UDP-NAM. This chain usually includes L-alanine, D-glutamic acid, meso-diaminopimelic acid or L-lysine, and two D-alanine residues. The product, UDP-NAM-pentapeptide, becomes the core building block for the later stages.

Next, the pathway moves to the membrane-associated phase. UDP-NAM-pentapeptide is transferred to bactoprenol phosphate, a lipid carrier in the inner leaflet of the plasma membrane, and this forms Lipid I. A NAG unit is then added to make Lipid II. Lipid II contains the complete disaccharide-pentapeptide structure. A flippase enzyme then moves Lipid II across the membrane to the periplasmic side, where the cell wall grows.

The final stage happens in the periplasm. Glycosyltransferases add the disaccharide-pentapeptide units to the growing peptidoglycan mesh by forming glycosidic bonds. The last step is transpeptidation, which is carried out by transpeptidase enzymes. This reaction releases the subunit from bactoprenol and creates peptide cross-links between neighboring stem peptides. These links strengthen the peptidoglycan layer and complete the synthesis process.

Building the Bacterial Cell Wall

prokaryotic vs. eukaryotic cells

Cell Organization in Prokaryotes and Eukaryotes

Prokaryotic and eukaryotic cells show two major patterns of cell organization. These differences shape the structure, size, and function of living things across the domains of life. Prokaryotic cells, such as bacteria and archaea, are simple in structure. They do not have a nucleus or other membrane-bound organelles. Their DNA is usually a single circular molecule found in the nucleoid region, which is not surrounded by a nuclear membrane. Prokaryotes are usually very small, about 0.1 to 5.0...

microbial morphologies 

Microbial Shapes and Cell Forms

Microbial shapes and cell forms help bacteria, archaea, and eukaryotic microbes survive in many environments. Cell shape affects how these organisms grow, take up nutrients, and handle waste. It also reflects the link between structure and function. Among bacteria, cocci and bacilli are the most common shapes. Cocci are spherical cells, and they may appear alone or in pairs called diplococci, chains called streptococci, clusters called staphylococci, or groups of four called tetrads. Bacilli...

bacterial cell wall 

Gram-Positive and Gram-Negative Walls

Bacterial cell walls give bacteria their shape and help protect them from osmotic stress. This rigid but flexible layer surrounds the plasma membrane and supports cellular integrity. Its main building block is peptidoglycan, a mesh-like polymer that adds strength while still allowing some flexibility. Peptidoglycan is made of alternating N-acetylglucosamine, or NAG, and N-acetylmuramic acid, or NAM. Short amino acid chains connect these sugar units and help form the strong network. The...

archaeal cell wall

Archaeal Cell Wall Types and Functions

Archaeal cell walls protect archaea and help them survive in extreme environments. Unlike bacterial cell walls, they do not have the peptidoglycan layer found in most bacteria. Instead, archaea use a range of materials, including proteins, polysaccharides, and pseudomurein, to build their outer layer. The most common archaeal cell wall is the S-layer, or surface layer. It is made of tightly packed protein or glycoprotein units that form a crystalline lattice. These repeating patterns can make...

peptidoglycan synthesis

Peptidoglycan builds the bacterial cell wall and gives the cell its shape and strength. It is a mesh-like polymer around the bacterial plasma membrane. The polymer is made of repeating sugar units, N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM), linked by β-1,4 glycosidic bonds. Short peptide chains cross-link the sugar chains and make the wall more rigid. Peptidoglycan biosynthesis starts in the cytoplasm with soluble precursors. Uridine diphosphate, or UDP, binds to NAG and NAM to...

plasma membrane in bacteria and archaea

Bacterial vs Archaeal Membrane Lipids

Bacterial and archaeal plasma membranes control what enters and leaves the cell. They also help maintain cell integrity. Although both membranes do the same basic job, their structures are different because bacteria and archaea face different environmental demands. Bacterial plasma membranes are mainly made of phospholipids. These lipids have fatty acid chains linked to a glycerol backbone by ester bonds. They form a bilayer, with hydrophilic glycerol-phosphate heads facing outward and...

outer layers of the cell envelope

Capsules, Slime Layers, and S-Layers

Capsules, slime layers, and S-layers are outer coverings on prokaryotic cells. These layers help bacteria and archaea survive, attach to surfaces, and interact with their environment. They are often made of polysaccharides, polypeptides, proteins, or glycoproteins. Capsules are tightly bound and highly organized layers that stick firmly to the bacterial cell wall. They are usually made of polysaccharides, although some are made of polypeptides. A capsule protects cells from dehydration and can...

flagella and motility in bacteria

Bacterial Flagella as Tiny Rotary Motors

Bacterial flagella are thread-like structures that help cells move and respond to their surroundings. They extend from the cell envelope and support both motility and chemotaxis, which is the ability to move in response to chemical signals. Their design shows how bacteria use specialized structures to survive in different environments. A flagellum has three main parts: the filament, the hook, and the basal body. The filament is the long, helical part made of repeating flagellin protein...

fimbriae, pili, and axial filaments

How Bacteria Stick, Share Genes, and Move

Fimbriae, pili, and axial filaments are bacterial surface structures that help cells attach, exchange genes, and move. These hairlike appendages are made mainly of pilin protein. They support bacterial survival in different environments and can also increase pathogenicity. Fimbriae are fine, filament-like structures that are densely packed on the bacterial surface. They are about 2 to 10 nanometers wide and help bacteria attach to nonliving surfaces and to host tissues. This adhesion is an...

cell inclusions

Prokaryotic Cell Storage Inclusions

Prokaryotic cell storage inclusions help bacteria store nutrients, manage energy, and adapt to changing environments. These inclusions let cells survive when food, phosphate, sulfur, light, or oxygen levels change. They are important examples of how simple cells can still have highly specialized structures. Some inclusions store carbon. Poly-β-hydroxybutyric acid, or PHB, forms granules that act as a long-term carbon and energy reserve. Glycogen granules also store carbon, but they provide a...

endospores and sporulation

How Bacteria Survive with Endospores

Endospores help some bacteria survive harsh conditions. These dormant cells are made mainly by Gram-positive bacteria such as Bacillus and Clostridium. They are highly resistant to heat, ultraviolet and ionizing radiation, drying, and toxic chemicals. In rare cases, endospore-like structures have also been seen in some Gram-negative bacteria, including Coxiella burnetii and Sporosarcina ureae, as well as in other species exposed to extreme conditions. Sporulation begins when bacteria face...

nucleoid

How Prokaryotes Organize DNA

Prokaryotes organize their DNA in the nucleoid, a distinct region where genetic material and associated proteins are packed. Because prokaryotic cells do not have a membrane-bound nucleus, the nucleoid helps keep DNA organized and available for cell activities. In most bacteria and archaea, the DNA is a single, circular, double-stranded molecule that is tightly compacted by supercoiling and protein interactions. Nucleoid-associated proteins, or NAPs, help shape and maintain this DNA region.

surface appendages of archaea

Archaeal Pili and Archaella in Action

Archaeal pili and archaella help archaea survive, attach, and move in challenging environments. These surface appendages support adhesion, biofilm formation, and motility. They give archaeal cells key advantages in habitats that can be extreme. Pili are filament-like structures made from pilin protein subunits. Their main role is adhesion, which means helping cells stick to surfaces. They also support biofilm formation, where cells live in a shared, surface-attached community. Some pili are...

key terms and concepts

Follow peptidoglycan cell wall assembly from cytoplasm to periplasm, including UDP-NAM precursors, Lipid I and II, flippase, and cross-linking.

Building the Bacterial Cell Wall | JoVE K12

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BIO.4.e

Building the Bacterial Cell Wall

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