Volume 86 Issue 49 | p. 15
Issue Date: December 8, 2008

Cover Stories: Genes To Gasoline

Lignocellulose: A Complex Biomaterial

Department: Science & Technology | Collection: Green Chemistry
Credit: Genome Management Information System/ORNL
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Credit: Genome Management Information System/ORNL

Plant cell walls are complex structures composed mostly of lignocellulose—the most abundant organic material on Earth—which is a matrix of cross-linked polysaccharide networks, glycosylated proteins, and lignin. This matrix has three main components: cellulose (38–50%), hemicellulose (17–32%), and lignin (15–30%).

Cellulose is a polysaccharide consisting of a linear chain of several hundred to more than 10,000 d-glucose units linked by β-1,4 bonds. This bonding motif differs from the α-1,4 glucose linkage of starch, such as cornstarch that comes from corn kernels.

This structural difference proves to be quite significant. Cellulose chains are linear and somewhat rigid, but starch takes on a coiled chain structure. That makes the cellulose chains amenable to forming numerous hydrogen bonds, which, unlike starch, leads the cellulose chains to assemble into cablelike bundles of crystalline fibrils that have high tensile strength and are resistant to hydrolysis to glucose.

Hemicellulose is also a polysaccharide, but it is typically made up of chains of xylose interspersed with side chains containing arabinose, galactose, mannose, glucose, acetyl, and other sugar groups, depending on plant type. Hemicellulose contains 500 to 3,000 sugar units and includes a small amount of pectin, another polysaccharide, with which it forms a cross-linked network.

Lignin is a cross-linked macromolecule composed of three types of substituted phenols (phenylpropanoids). It fills the spaces in the cell wall between cellulose, hemicellulose, and pectin and is covalently linked to hemicellulose. Lignin resembles a kind of phenol-formaldehyde resin that acts like glue to hold the lignocellulose matrix together. Lignin helps provide additional strength to cell walls and resistance to insects and diseases.

 

Cover Story

 
Chemical & Engineering News
ISSN 0009-2347
Copyright © American Chemical Society
Comments
Thiago Gomes (Wed Jan 29 20:54:46 EST 2014)
This is not actually a comment, but a question: I would like to know whether I could use that picture illustrating plant cell wall composition in my Ph. D. thesis or to whom I should ask for permission. The thesis is a nonprofit, academic work, and will be available online. Thanks in advance.
Steve Ritter (Mon Feb 03 11:12:23 EST 2014)
This graphic was once available at the Department of Energy's
Office of Biological and Environmental Research image gallery. I am not sure if it is still there but you can check at the following website https://public.ornl.gov/site/gallery/default.cfm. If not, There are related images there that might work. You will need to read the description about how to use the images, but they should be available for you to use. Good luck.

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