Bacterial cell structure pdf

Their structural simplicity makes S-layers a suitable model for analyzing structure-function relationships as well as dynamic aspects of membrane morphogenesis. It provides details of methods available for the preparation of cell walls and their components. All the sections are written by researchers with first-hand practical experience of the techniques. The book concentrates on techniques that are available to most laboratories and provides complete information for workers new to the field, while at the same time serving as a valuable reference work for those already engaged in cell-surface research.

Knowledge of the biochemistry of the cell wall components and the genetic background helps to understand their significance with regard to microbiology and immunology of bacteria.

This book represents the second edition of a publication which was presented nearly 20 years ago in the German language Die bakterielle Zellwand. Since that time our knowledge in this field has been significantly enlarged. Why study bacterial cell walls? They are essential structures in bacteria.

They are made of chemical components found nowhere else in nature. They may cause symptoms of disease in animals. They are the site of action of some of our most important antibiotics. Gram-positive cell wall is thick homogeneous monolayer Gram-negative cell wall is thin heterogeneous multilayer. To prevent rupture or osmotic lysis of the cell protoplast Lysis of a pair of dividing E. Bacterial cell walls always contain murein, which is a type of peptidoglycan.

Other characteristics of bacterial cell walls Gram-positive cell walls contain teichoic acids. Teichoic acids are thought to stabilize the Gram positive cell wall and may be used in adherence. Other characteristics of bacterial cell walls Gram-negative cell walls include an outer membrane.

Other characteristics of bacterial cell walls Outer membrane of Gram-negatives has two important properties 1. It protects the cells from permeability by many substances including penicillin and lysozyme.

It is the location of lipopolysaccharide endotoxin which is toxic for animals. The proteins associate with both sides of the membrane, or may imbed in the membrane, or pass through the membrane. The cytoplasmic membrane of E.

Functions of the membrane during expression of virulence Functions permeability barrier to antibiotics or host defensins transport of nutrients export of toxic substances sensing the environment specialized enzymatic processes. Endospores are produced as intracellular structures within the cytoplasm of certain bacteria, most notably Bacillus and Clostridium species. Endospore forming bacteria left to right: Clostridium botulinum, Bacillus brevis, Bacillus thuringiensis. Resting dormant cells cryptobiotic i.

Several unique surface layers not found in vegetative cells: exosporium, spore coat, cortex, and core wall. Highly resistant to heat boiling , acids, bases, dyes dont stain irradiation, disinfectants, antibiotics, etc. Endospore formation is NOT a mechanism of reproduction.

Rather it is a mechanism for survival in deleterious environments. During the process of spore formation, one vegetative cell develops into one endospore. The sequential steps of endospore formation in a Bacillus species. The process of endospore formation takes about six hours. Eventually the mature endospore is released from its mother cell as a free spore Free endospore. Under favorable nutritional and environmental conditions, an endospore germinates into a vegetative cell.

Bacillus anthracis causes anthrax Bacillus cereus causes food poisoning Clostridium tetani causes tetanus Clostridium botulinum causes botulism Clostridium perfringens causes food poisoning and gas gangrene Clostridium difficile causes antibioticinduced diarrhea and pseudomembranous colitis.

Which are more sensitive to Penicllin? Chapter 4. Open navigation menu. Close suggestions Search Search. User Settings.

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There are two main types of teichoic acid: ribitol teichoic acids and glycerol teichoic acids. A major component of the gram-positive cell wall is lipoteichoic acid.

One of its purposes is providing an antigenic function. The Gram-negative cell wall Gram-negative cell walls are thin and unlike the Gram-positive cell walls, they contain a thin peptidoglycan layer adjacent to the cytoplasmic membrane. The chemical structure of the outer membrane's lipopolysaccharides is often unique to specific bacterial sub-species and is responsible for many Magrndira Mani Vinayagam Academia.

Lipopolysaccharides, also called endotoxins, are composed of polysaccharides and lipid A which are responsible for much of the toxicity of Gram-negative bacteria. It consists of characteristic lipopolysaccarides embedded in the membrane.

Plasma membrane The plasma membrane or bacterial cytoplasmic membrane is composed of a phospholipid bilayer and thus has all of the general functions of a cell membrane such as acting as a permeability barrier for most molecules and serving as the location for the transport of molecules into the cell and energy conservation.

As a phospholipid bilayer, the lipid portion of the outer membrane is impermeable to charged molecules. However, channels called porins are present in the outer membrane that allow for passive transport of many ions, sugars and amino acids across the outer membrane. These molecules are therefore present in the periplasm, the region between the cytoplasmic and outer membranes. The periplasm contains the peptidoglycan layer and many proteins responsible for substrate binding or hydrolysis and reception of extracellular signals.

Extracellular external structures Fimbrae and pili Fimbrae sometimes called "attachment pili" are protein tubes that extend out from the outer membrane in many members of the Proteobacteria. They are generally short in length and present in high numbers about the entire bacterial cell surface. Fimbrae usually function to Magrndira Mani Vinayagam Academia. A few organisms e. Myxococcus use fimbrae for motility to facilitate the assembly of multicellular structures such as fruiting bodies.

Pili are similar in structure to fimbrae but are much longer and present on the bacterial cell in low numbers. Pili are involved in the process of bacterial conjugation where they are called conjugation pili or "sex pili". Type IV pili non-sex pili also aid bacteria in gripping surfaces.

S-layers An S-layer surface layer is a cell surface protein layer found in many different bacteria and in some archaea, where it serves as the cell wall. The exact function of S-layers is unknown, but it has been suggested that they act as a partial permeability barrier for large substrates.

For example, an S-layer could conceivably keep extracellular proteins near the cell membrane by preventing their diffusion away from the cell. In some pathogenic species, an S-layer may help to facilitate survival within the host by conferring protection against host defence mechanisms.

Glycocalyx Many bacteria secrete extracellular polymers outside of their cell walls called glycocalyx. These polymers are usually composed of polysaccharides and some timesprotein. Capsules are relatively impermeable structures that cannot be stained with dyes such as India ink.

They are structures that help protect bacteria from phagocytosis and desiccation. Slime layer is involved in Magrndira Mani Vinayagam Academia. Slime layers can also be used as a food reserve for the cell. Flagella Flagella are whip-like structures protruding from the bacterial cell wall and are responsible for bacterial motility i. The arrangement of flagella about the bacterial cell is unique to the species observed.

A 10 overlaid structures, shown as a rainbow view, from blue at the N-terminus to red at the C-terminus. B Best structure as a cartoon, same colour scheme and orientation.

Labelling of helices and sheets follows that in [30]. MPB70 green. Superpositions and RMSD values in the text were based on the most highly conserved regions of secondary structure, corresponding to residues 45—50, 55— 4.

Discussion 65, 82—94, —, —, — and — from Fdp. Location of the protein interaction site Here we report the structure of a new member of the FAS1 family, which unusually has only a single FAS1 domain. This new member oxygen-dependent regulatory system Phillips-Jones et al. Robert G. Corneal dystrophy mutations affect structural integrity not binding There have been detailed studies of mutations in TGFBIp, which Fig. The binding surface on Fdp. A The surface of Fdp in partially transparent lead to a range of corneal dystrophies, characterized by amyloid-like view.

Conserved regions H1 and H2 are shown in red and blue respectively. They protein deposits in the eye. The N and C termini are indicated by spheres. The equivalent B Suggested binding surface of Fdp; residues 50, 52 and —, all other residues position to R is not well conserved in Fdp Fig. In the Drosophila FAS1 hydrophilic in magenta. The key binding residues D and V are indicated.

The structure, the equivalent residue is in a turn, and it was concluded orientation is the same as in A. The orange surface is domain 3 of Drosophila FAS1, from the crystal structure of domains 3 and 4 [30], oriented so that domain 4 aligns that it should also be exposed in TGFBIp, and consequently mutations with Fdp. For clarity, domain 4 is not shown.

For interpretation of the references to here could affect interactions with other proteins [30]. In support of resent an evolutionarily ancient cell adhesion domain, most likely this suggestion, we note that different mutations at R can have functioning by binding to cell-surface proteins [1,18]. We therefore either stabilizing or destabilizing effects [49,50]. Almost all the other looked for residues that are conserved across a wide range of species, disease-causing mutations are at sites that are buried in Fdp, and and are likely to be functionally important.

To this end, we have pre- are therefore likely to lead to instability and consequent amyloid pared a new sequence alignment that is based on structural similarity formation, rather than loss of interactions, as also suggested by others rather than simply sequence similarity, using the existing structures [27,29,30,32].

Our structure of Fdp is important in guiding the align- ment, because of the low level of sequence similarity between ex- 4. The interaction site is at the dimer interface isting sequences, and the presence of insertions and deletions. The alignment is shown in Fig. These regions are adjacent in the structure, and form tein Fig. Thus much of most exposed region of the protein, as expected. In these maintaining the structure, leaving the most likely binding site as the proteins, the FAS1 domains generally occur in pairs.

An analysis of M. The importance of the C-terminal domain can the same region as being important, together with other residues on also be seen by sequence comparisons of Drosophila FAS1, TGFBIp the opposite face of the protein that were suggested to form a second and periostin Fig.

The best-supported site is the two residues DI much more highly conserved in domains 2 and 4 i. These residues have been domain from each pair than in the other two domains [51].

The clear implication is thetic pentapeptides containing this sequence blocked cell adhesion that the binding site in these proteins is located mainly or entirely [8,17,46]. However, His72 is largely buried in both intermolecular binding Fig. The key residues D and V are Fdp and FAS1, implying that it is unlikely to be involved in protein almost completely buried in the interface Fig.

Further support recognition [47]. In Fdp these are generally either absent or buried, again terface between domains 3 and 4, which could potentially disrupt the making it unlikely that this site is important for Fdp. We conclude that domain reorientation. Inspec- function, and that our imputation of a binding region here is incorrect.