Bacterial and Archaea Structure and Function. • Prokaryotes differ from eukaryotes in size and simplicity. – most lack internal membrane systems. Localization of Other Proteins Involved in Bacterial Cell Wall Synthesis. Actin Homologues in Bacteria and Their Role in Cell Wall Synthesis. The location of the mucopeptide in the cell wall of Bacteroides convexus was deter- mined by electron microscope after enzymatic and chemical treatment.

Bacterial Cell Wall Pdf

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Abstract: Peptidoglycan is the major component of the cell envelope of virtually all bacteria. It has structural roles and acts as a selective sieve. The bacterial cell wall represents a very complex structure disconnecting the Pages PDF · The Outer Membrane of the Gram-Negative Bacteria and their. The 3D structure of the bacterial peptidoglycan, the major constit- uent of the cell wall, is one of the most important, yet still unsolved, structural.

Bacterial DNA is naked lacked histone protein Function: It contains and stores hereditary information of the cell.

It controls all cell activities. Ribosome: Bacterial ribosome is of 70s type. Ribosomes are rounded granules found freely floating in the cytoplasm Ribosomes are known as universal cell organelle because it is found in both bacterial cell and eukaryotic cell. Chemically the ribosomes are made up of nucleic acids particularly RNA and proteins.

Function: It helps in protein synthesis Mesosome: Mesosome is a spherical or round sac like structure found commonly in gram positive bacteria. Function: It is the site for respiration in bacterial cell Cytoplasm: It is colorless, viscus fluid present inside cell membrane. All the cell organelles and inclusions are found floating in cytoplasmic fluid.

It contains proteins, lipid, minerals, nucleic acids, glycogen, water etc.

Bacterial Cell Wall, Volume 27

Function: It helps to distribute water, oxygen as other substances throughout the cell. Literally, all the cellular content including nucleus, and other cell organelle are floating in cytoplasm.

Spores endospore : Spore is metabolically dormant structure produced during unfavourable condition by the process called sporulation Sporulation occur during late log phase or early stationary phase Under favourable condition spores germinate to give vegetative cell.

Gram-positive bacteria: These bacteria stain violet by Gram staining. It is based on the chemical and physical properties of their cell walls. Primarily, it detects peptidoglycan, which is present in a thick layer in Gram-positive bacteria.


The Gram stain is almost always the first step in the identification of a bacterial organism, and is the default stain performed by laboratories over a sample when no specific culture is referred. In Gram-positive bacteria, the cell wall is thick nanometers , and consists of several layers of peptidoglycan.

They lack the outer membrane envelope found in Gram-negative bacteria. Running perpendicular to the peptidoglycan sheets is a group of molecules called teichoic acids, which are unique to the Gram-positive cell wall. Teichoic acids are linear polymers of polyglycerol or polyribitol substituted with phosphates and a few amino acids and sugars. The teichoic acid polymers are occasionally anchored to the plasma membrane called lipoteichoic acid, LTA , and apparently directed outward at right angles to the layers of peptidoglycan.

Teichoic acids give the Gram-positive cell wall an overall negative charge due to the presence of phosphodiester bonds between teichoic acid monomers.

The functions of teichoic acid are not fully known but it is believed to serve as a chelating agent and means of adherence for the bacteria. These are essential to the viability of Gram-positive bacteria in the environment and provide chemical and physical protection. One idea is that they provide a channel of regularly-oriented, negative charges for threading positively-charged substances through the complicated peptidoglycan network.

Another theory is that teichoic acids are in some way involved in the regulation and assembly of muramic acid sub-units on the outside of the plasma membrane. There are instances, particularly in the streptococci, wherein teichoic acids have been implicated in the adherence of the bacteria to tissue surfaces and are thought to contribute to the pathogenicity of Gram-positive bacteria.

Mycoplasmas and Other Cell-Wall-Deficient Bacteria Some bacteria lack a cell wall but retain their ability to survive by living inside another host cell. Learning Objectives Distinguish between bacteria with and without cell walls Key Takeaways Key Points Examples of bacteria that lack a cell wall are Mycoplasma and L-form bacteria.

Mycoplasma is an important cause of disease in animals and is not affected by antibiotic treatments that target cell wall synthesis. Mycoplasma acquire cholesterol from the environment and form sterols to build their cytoplasmic membrane.

Key Terms osmotic environment: environment with controlled net movement of molecules from a region of high solvent concentration to a region of low solvent concentration through a permeable membrane. For most bacterial cells, the cell wall is critical to cell survival, yet there are some bacteria that do not have cell walls.

Mycoplasma species are widespread examples and some can be intracellular pathogens that grow inside their hosts.

This bacterial lifestyle is called parasitic or saprophytic. Cell walls are unnecessary here because the cells only live in the controlled osmotic environment of other cells. It is likely they had the ability to form a cell wall at some point in the past, but as their lifestyle became one of existence inside other cells, they lost the ability to form walls.

L-form bacteria: L-form bacterial lack a cell wall structure. Consistent with this very limited lifestyle within other cells, these microbes also have very small genomes. They have no need for the genes for all sorts of biosynthetic enzymes, as they can steal the final components of these pathways from the host.

The Bacterial Cell Wall

Similarly, they have no need for genes encoding many different pathways for various carbon, nitrogen and energy sources, since their intracellular environment is completely predictable. Because of the absence of cell walls, Mycoplasma have a spherical shape and are quickly killed if placed in an environment with very high or very low salt concentrations.

However, Mycoplasma do have unusually tough membranes that are more resistant to rupture than other bacteria since this cellular membrane has to contend with the host cell factors. The presence of sterols in the membrane contributes to their durability by helping to increase the forces that hold the membrane together.

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Other bacterial species occasionally mutate or respond to extreme nutritional conditions by forming cells lacking walls, termed L-forms.

This phenomenon is observed in both gram-positive and gram-negative species. L-forms have varied shapes and are sensitive to osmotic shock. Cell Walls of Archaea Archaeal cell walls differ from bacterial cell walls in their chemical composition and lack of peptidoglycans.

Learning Objectives State the similarities between the cell walls of archaea and bacteria Key Takeaways Key Points Archaea are single-celled microorganisms that lack a cell nucleus and membrane -bound organelles. Like other living organisms, archaea have a semi-rigid cell wall that protects them from the environment. The cell wall of archaea is composed of S-layers and lack peptidoglycan molecules with the exception of methanobacteria who have pseudopeptidoglycan in their cell wall.

Key Terms cellulose: A complex carbohydrate that forms the main constituent of the cell wall in most plants and is important in the manufacture of numerous products, such as paper, textiles, pharmaceuticals, and explosives. It includes cytosol, organelles, vesicles, and the cytoskeleton.

As with other living organisms, archaeal cells have an outer cell membrane that serves as a protective barrier between the cell and its environment. Within the membrane is the cytoplasm, where the living functions of the archeon take place and where the DNA is located.

Around the outside of nearly all archaeal cells is a cell wall, a semi-rigid layer that helps the cell maintain its shape and chemical equilibrium.

All three of these regions may be distinguished in the cells of bacteria and most other living organisms. Archaea: Cluster of halobacterium archaea A closer look at each region reveals structural similarities but major differences in chemical composition between bacterial and archaeal cell wall.

Archaea builds the same structures as other organisms, but they build them from different chemical components. For instance, the cell walls of all bacteria contain the chemical peptidoglycan. Archaeal cell walls do not contain this compound, though some species contain a similar one. It is assembled from surface-layer proteins called S-layers.

Likewise, archaea do not produce walls of cellulose as do plants or chitin as do fungi. The cell wall of archaeans is chemically distinct. Methanogens are the only exception and possess pseudopeptidoglycan chains in their cell wall that lacks amino acids and N-acetylmuramic acid in their chemical composition.

The most striking chemical differences between Archaea and other living things lie in their cell membrane. There are four fundamental differences between the archaeal membrane and those of all other cells: 1 chirality of glycerol, 2 ether linkage, 3 isoprenoid chains, and 4 branching of side chains. Damage to the Cell Wall The cell wall is responsible for bacterial cell survival and protection against environmental factors and antimicrobial stress.

Learning Objectives Discuss the effects that damage to the cell wall has on the bacterial cell Key Takeaways Key Points Gram-positive and Gram-negative bacteria are protected by an external cell wall composed of varying layers of peptidoglycan.

Damage to bacterial cell wall compromises its integrity and creates imbalance of electrolytes that trigger cell death.Penicillin mechanism of action: Penicillin acts by binding to penicillin binding proteins and inhibiting the cross-linking of peptidoglycan subunits. Cell membrane of bacteria is composed of phospholipid and proteins. English Copyright: Personal information is secured with SSL technology. This type of cell wall is composed entirely of a thick layer of polysaccharides , which may be sulfated in the case of Halococcus.

Institutional Subscription. Consistent with this very limited lifestyle within other cells, these microbes also have very small genomes.