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

Peptidoglycan, a key bacterial cell wall component, is made of alternating N-acetylglucosamine, or NAG, and N-acetylmuramic acid or NAM units joined by &#946;-1,4 glycosidic bonds.Peptidoglycan synthesis involves three phases. In the cytoplasm, uridine diphosphate (UDP) molecules are covalently attached to NAG.UDP-NAG gets enzymatically converted to UDP-NAM. Then, a pentapeptide chain is added to UDP-NAM to form a UDP-NAM-pentapeptide.In the membrane-associated phase, the NAM-pentapeptide is linked to bactoprenol phosphate, forming Lipid I on the cytoplasmic side of the plasma membrane.The addition of a NAG unit to Lipid I forms Lipid II, which is translocated across the membrane to the periplasm by a flippase.In the periplasmic phase, glycosyltransferases form glycosidic bonds to add the NAG-NAM-pentapeptide to the growing peptidoglycan chain attached to bactoprenol.In the final step, the transpeptidase enzyme forms peptide cross-links between glycan chains, releases the chain from bactoprenol, and completes synthesis by linking stem peptides.

peptidoglycan synthesis

Structure of PeptidoglycanPeptidoglycan is a vital structural component of the bacterial cell wall, providing mechanical strength and shape to the cell. It consists of repeating units of two sugars&#8212;N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)&#8212;linked by &#946;-1,4 glycosidic bonds. These sugar chains are cross-linked by short peptide chains, forming a mesh-like polymer that surrounds the bacterial plasma membrane.Cytoplasmic Phase &#8211; Precursor SynthesisPeptidoglycan biosynthesis begins in the cytoplasm with the formation of soluble precursors. In this stage, uridine diphosphate (UDP), an ester of pyrophosphoric acid, binds to NAG and NAM to form UDP-NAG and UDP-NAM, respectively. UDP-NAG is then enzymatically converted into UDP-NAM. A pentapeptide chain&#8212;typically composed of L-alanine, D-glutamic acid, meso-diaminopimelic acid (or L-lysine), and two D-alanine residues&#8212;is sequentially added to UDP-NAM, forming UDP-NAM-pentapeptide. This compound serves as the foundational building block for later stages of peptidoglycan synthesis.Membrane-Associated Phase &#8211; Lipid Carrier TransferIn the membrane-associated phase, the UDP-NAM-pentapeptide is transferred to bactoprenol phosphate, a lipid carrier embedded in the inner leaflet of the plasma membrane. This transfer results in the formation of Lipid I. Next, a NAG unit is added to Lipid I, generating Lipid II, which now contains the complete disaccharide-pentapeptide structure. A flippase enzyme then translocates Lipid II across the membrane, delivering the precursor to the periplasmic side for incorporation into the growing cell wall.Periplasmic Phase &#8211; Polymerization and Cross-LinkingIn the final phase, located in the periplasm, glycosyltransferases incorporate the disaccharide-pentapeptide units into the existing peptidoglycan mesh by catalyzing the formation of glycosidic bonds. The last step, known as transpeptidation, is carried out by transpeptidase enzymes. This reaction releases the subunit from bactoprenol and forms peptide cross-links between adjacent stem peptides, reinforcing the structural integrity of the peptidoglycan layer and completing the biosynthesis process.

Structure of PeptidoglycanPeptidoglycan is a vital structural component of the bacterial cell wall, providing mechanical strength and shape to the cell. ...

Education

JoVE Core

Microbiology

Unit

Microbial Cell Structure and Function        

KEY TERMS AND CONCEPTS

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 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

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flagella and motility in bacteria

Bacterial Flagella as Tiny Rotary Motors

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fimbriae, pili, and axial filaments

How Bacteria Stick, Share Genes, and Move

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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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