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

Peptidoglykan, eine Schlüsselkomponente der bakteriellen Zellwand, besteht aus abwechselnd N-Acetylglucosamin (NAG) und N-Acetylmuramsäure (NAM) Einheiten, die durch β-1,4-Glykosidbindungen verbunden sind. Die Peptidoglycansynthese umfasst drei Phasen. Im Zytoplasma sind Uridindiphosphat (UDP)-Moleküle kovalent an NAG gebunden. UDP-NAG wird enzymatisch in UDP-NAM umgewandelt. Dann wird eine Pentapeptidkette an UDP-NAM angehängt, um ein UDP-NAM-Pentapeptid zu bilden. In der membranassoziierten Phase ist das NAM-Pentapeptid an Bactoprenolphosphat gebunden und bildet auf der zytoplasmatischen Seite der Plasmamembran das Lipid I. Die Zugabe einer NAG-Einheit zu Lipid I bildet Lipid II, das durch eine Flippase über die Membran in das Periplasma transloziert wird. In der periplasmatischen Phase bilden Glykosyltransferasen glykosidische Bindungen, um das NAG-NAM-Pentapeptid an die wachsende Peptidoglycankette anzuhängen, die an Bactoprenol gebunden ist. Im letzten Schritt bildet das Transpeptidase-Enzym Peptidvernetzungen zwischen Glykanketten, befreit die Kette von Bactoprenol und schließt die Synthese ab, indem es Stammpeptide verknüpft.

peptidoglykansynthese

Struktur des Peptidoglykans
Peptidoglykan ist ein essenzieller Strukturbestandteil der bakteriellen Zellwand, der der Zelle mechanische Festigkeit und Form verleiht. Es besteht aus sich wiederholenden Einheiten von zwei Zuckern &#8211; N-Acetylglucosamin (NAG) und N-Acetylmuramins&#228;ure (NAM) &#8211; die durch &#946;-1,4-glykosidische Bindungen verkn&#252;pft sind. Diese Zuckerketten werden durch kurze Peptidketten quervernetzt und bilden ein netzartiges Polymer, das die bakterielle Plasmamembran umgibt.
Zytoplasmatische Phase &#8211; Synthese der Vorl&#228;ufer
Die Biosynthese von Peptidoglykan beginnt im Zytoplasma mit der Bildung l&#246;slicher Vorl&#228;ufer. In dieser Phase bindet Uridindiphosphat (UDP), ein Ester der Pyrophosphors&#228;ure, an NAG bzw. NAM und bildet UDP-NAG bzw. UDP-NAM. Anschlie&#223;end wird UDP-NAG enzymatisch zu UDP-NAM umgewandelt. An UDP-NAM wird schrittweise eine Pentapeptidkette angeh&#228;ngt, die typischerweise aus L-Alanin, D-Glutamins&#228;ure, meso-Diaminopimelins&#228;ure (oder L-Lysin) und zwei D-Alanin-Resten besteht. Es entsteht das UDP-NAM-Pentapeptid, welches die grundlegende Baueinheit f&#252;r die folgenden Syntheseschritte darstellt.
Membranassoziierte Phase &#8211; &#220;bertragung durch Lipidtr&#228;ger
In der membranassoziierten Phase wird das UDP-NAM-Pentapeptid auf Bactoprenolphosphat &#252;bertragen &#8211; ein Lipidtr&#228;ger, der in der inneren Schicht der Plasmamembran verankert ist. Dadurch entsteht Lipid I. Anschlie&#223;end wird eine NAG-Einheit zu Lipid I hinzugef&#252;gt, wodurch Lipid II gebildet wird, das die vollst&#228;ndige Disaccharid-Pentapeptidstruktur enth&#228;lt. Ein Flippase-Enzym transloziert Lipid II dann &#252;ber die Membran und bringt den Vorl&#228;ufer auf die periplasmatische Seite, wo er in die wachsende Zellwand eingebaut wird.
Periplasmatische Phase &#8211; Polymerisierung und Quervernetzung
In der letzten Phase, die im Periplasma stattfindet, bauen Glykosyltransferasen die Disaccharid-Pentapeptid-Einheiten in das bestehende Peptidoglykan-Netz ein, indem sie die Bildung glykosidischer Bindungen katalysieren. Der abschlie&#223;ende Schritt, die sogenannte Transpeptidation, wird von Transpeptidase-Enzymen durchgef&#252;hrt. Dabei wird die Untereinheit von Bactoprenol freigesetzt und Peptidquervernetzungen zwischen benachbarten Stammpeptiden gebildet, wodurch die strukturelle Integrit&#228;t der Peptidoglykanschicht verst&#228;rkt und der Syntheseprozess abgeschlossen wird.

Peptidoglykansynthese

Struktur des Peptidoglykans
Peptidoglykan ist ein essenzieller Strukturbestandteil der bakteriellen Zellwand, der der Zelle mechanische Festigkeit und ...

Education

Lehre

JoVE Core

Microbiology

Mikrobiologie

Unit

Einheit

Microbial Cell Structure and Function        

Mikrobielle Zellstruktur und Funktion

KEY TERMS AND CONCEPTS

KERNBEGRIFFE UND KONZEPTE

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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