Bacterial Cell Wall Synthesis: ..

Other candidates for enzymes involved include: (1) pectin methyl esterase which would break the calcium bridges between pectins by esterifying the carboxyl groups; and (2) hydrolases – which would hydrolyze the cross-linking glycans (hemicelluloses). For example, xyloglucan endotransglycosylase (XET) has been shown to cleave cross-linking glycans that could allow slippage of the wall components

Incorporation of new cell wall in differently shaped bacteria

In both gram-positive and gram-negative bacteria, the scaffold of the cell wall consists of the ..

Antibacterial Inhibitors of Cell Wall Synthesis

When the Gram stain was developed by Hans Christian Gram in 1884 the molecular basis of the stain was unknown. In fact very little was understood about bacteria in general. He just determined empirically that when bacterial smears were run through a four-step staining procedure using two different dyes, some cells retained the first dye and stained purple, while other only retained the second dye and stained pink. Years later it was discovered that the basis for this differential reaction relates to the cell wall as shown in .

Antibiotics; Inhibitors of Cell Wall Synthesis

The structure and synthesis of prokaryotic cell walls is unique and many compounds found in the bacterial cell wall are found nowhere else in nature. It is true that plants also make cell walls, but they are chemically and structurally different. There are two basic types of bacterial cell wall structures that have been studied in detail: gram-positive and gram-negative. These two classes of bacterial cells look very different following staining with the Gram stain and this has been a standard basis for starting to identify different bacterial species. Figures 2-36 and 2-37 show Gram stains of gram-positive and gram-negative bacteria, respectively.

The matrix of the wall is analogous tothe rubber in the tire and is comprised of non-cellulosic wall components.

Bacterial Cell Structure and Function

Oligosaccharins, which can result from normal development or pathogen attack, serve a variety of functions including: (a) stimulate ethylene synthesis; (b) induce phytoalexin (defense chemicals produced in response to a fungal/bacterial infection) synthesis; (c) induce chitinase and other enzymes; (d) increase cytoplasmic calcium levels and (d) cause an "oxidative burst". This burst produces hydrogen peroxide, superoxide and other active oxygen species that attack the pathogen directly or cause increased cross-links in the wall making the wall harder to penetrate.

Let's look at how this system works. Consider a pathogenic fungus like . In contact with the host plant the fungus releases enzymes such as pectinase that break down plant wall components into oligosaccharins. The oligosaccharins stimulate the oxidative burst and phytoalexin synthesis, both which will deter the advance of the fungus. In addition, the oligosaccharins stimulate chitinase and glucanase production in the plant. These are released and begin to digest the fungal wall. Fragments of fungal wall also act as oligosaccharins in the plant to further induce phytoalexin synthesis. Cool!

Functions of the cell wall

Inhibition of Cell Wall Biosynthesis

Bacteria growing in a suitable medium increase in number by having each cell increase in size, and then each cell divides to produce two daughter cells. The increase in cell number in a culture is, therefore, a result of the activity of the cell during the division cycle, between the period of birth by division and the subsequent division. There is a close relation between the composition of the growth medium and the bacterial growth rate and Deoxyribonucleic acid (DNA) replication. The exponential growth of bacteria can be understood from the increase of cellular material, such as ribonucleic acid and protein, which, in turn, generate more cellular components. Recent studies have revealed a relation between the cell cycle and the control of initiation of DNA replication, cell division and cell surface synthesis.

The actual content of the wall components varies with species and age. All plant cells have a middle lamella and primary wall.

Peptidoglycan layer is also the structure of bacterial cell wall

Erythromycin and other macrolide antibiotics inhibit protein synthesis by binding to the 23S rRNA molecule (in the 50S subunit) of the bacterial ribosome blocking the exit of the growing peptide chain. of sensitive microorganisms. (Humans do not have 50 S ribosomal subunits, but have ribosomes composed of 40 S and 60 S subunits). Certain resistant microorganisms with mutational changes in components of this subunit of the ribosome fail to bind the drug. The association between erythromycin and the ribosome is reversible and takes place only when the 50 S subunit is free from tRNA molecules bearing nascent peptide chains. Gram-positive bacteria accumulate about 100 times more erythromycin than do gram-negative microorganisms. The non ionized from of the drug is considerably more permeable to cells, and this probably explains the increased antimicrobial activity that is observed in alkaline pH.

Comparison of the thick cell wall of Gram-positive bacteria with the comparatively thin cell wall of Gram-negative bacteria

to 60% of the cell wall mass in gram-positive bacteria.

Presentation Summary : PowerPoint lecture on the Bacterial Cell Wall and Differential Staining used in an actual college microbiology classroom.