The following sections of this BookRags Literature Study Guide is offprint from Gale's For Students Series: Presenting Analysis, Context, and Criticism on Commonly Studied Works: Introduction, Author Biography, Plot Summary, Characters, Themes, Style, Historical Context, Critical Overview, Criticism and Critical Essays, Media Adaptations, Topics for Further Study, Compare & Contrast, What Do I Read Next?, For Further Study, and Sources.
(c)1998-2002; (c)2002 by Gale. Gale is an imprint of The Gale Group, Inc., a division of Thomson Learning, Inc. Gale and Design and Thomson Learning are trademarks used herein under license.
The following sections, if they exist, are offprint from Beacham's Encyclopedia of Popular Fiction: "Social Concerns", "Thematic Overview", "Techniques", "Literary Precedents", "Key Questions", "Related Titles", "Adaptations", "Related Web Sites". (c)1994-2005, by Walton Beacham.
The following sections, if they exist, are offprint from Beacham's Guide to Literature for Young Adults: "About the Author", "Overview", "Setting", "Literary Qualities", "Social Sensitivity", "Topics for Discussion", "Ideas for Reports and Papers". (c)1994-2005, by Walton Beacham.
All other sections in this Literature Study Guide are owned and copyrighted by BookRags, Inc.
Peptidoglycan is the skeleton of bacteria. Present in both Gram-positive and Gram-negative bacteria, the peptidoglycan is the rigid sac that enables the bacterium to maintain its shape.
This rigid layer is a network of two sugars that are cross-linked together by amino acid bridges. The sugars are N-acetyl glucosamine and N-acetyl muramic acid. The latter sugar is unique to the peptidoglycan, and is found no where else in nature.
The peptidoglycan in Gram-negative bacteria is only a single layer thick, and appears somewhat like the criss-cross network of strings on a tennis racket. The layer lies between the two membranes that are part of the cell wall of Gram-negative bacteria, and comprises only about twenty percent of the weight of the cell wall. In Gram-positive bacteria, the peptidoglycan is much thicker, some 40 sugars thick, comprising up to ninety percent of the weight of the cell wall. The cross bridging is three-dimensional in this network. The peptidoglycan layer is external to the single membrane, and together they comprise the cell wall of Gram-positive bacteria.
Research has demonstrated that the growth of the peptidoglycan occurs at sites all over a bacterium, rather than at a single site. Newly made peptidoglycan must be inserted into the existing network in such a way that the strength of the peptidoglycan sheet is maintained. Otherwise, the inner and outer pressures acting on the bacterium would burst the cell. This problem can be thought of as similar to trying to incorporate material into an inflated balloon without bursting the balloon. This delicate process is accomplished by the coordinate action of enzymes that snip open the peptidoglycan, insert new material, and bind the old and new regions together. This process is also coordinated with the rate of bacterial growth. The faster a bacterium is growing, the more quickly peptidoglycan is made and the faster the peptidoglycan sac is enlarged.
Certain antibiotics can inhibit the growth and proper linkage of peptidoglycan. An example is the beta-lactam class of antibiotics (such as penicillin). Also, the enzyme called lysozyme, which is found in the saliva and the tears of humans, attacks peptidoglycan by breaking the connection between the sugar molecules. This activity is one of the important bacterial defense mechanisms of the human body.