**2. Structure and composition of the cell wall**

It has been estimated that the net CO2 fixation by land plants per year is approximately 56 X 109 tons and that the worldwide biomass production by land plants is 170–200 X 109 tons (Table 1). Of this amount, 70% is estimated to represent plant cell walls (revised in [9]).

Lignocellulose is a renewable organic material and is the major structural component of all cell plants. Lignocellulose plant biomass consists of three major components: cellulose (40– 50 %), hemicellulose (20–40 %) and lignin (20–30 %) (Figure 1).

**Figure 1.** Structural organization of the plant cell wall. Cellulose is protected of degradation by hemicelluloses and lignin. Source: Office of Biological and Environmental Research of the U.S. Department of Energy Office of Science.

Hydrolysis of Biomass Mediated by Cellulases for the Production of Sugars

http://dx.doi.org/10.5772/53719

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Cell walls should play a wide array of disparate and sometimes opposing roles: the resist‐ ance to mechanical stress is necessary as well as the shape of the cell and protection against pathogens; at the same time, besides it must be reasonably flexible to withstand shear forces,

Cellulose is the main component in the plant cell walls, and is made of parallel unbranched D-glucopyranose units linked by β-1,4-glycosidic bonds that form crystalline and highly or‐ ganized microfibrils through extensive inter and intramolecular hydrogen bonds and Van der Waals forces, amorphous cellulose correspond to regions where this bonds are broken and the ordered arrangement is lost (Figure 2).The cellulose chains aggregated into microfi‐ brils are reported to consist of 24 to 36 chains based on scattering data and information

Consecutive glucose molecules along chains in crystalline cellulose are rotated by 180º,

meaning that the disaccharide (cellobiose) is the repeating unit [22].

and permeable enough to allow the passage of signalling molecules into the cell [19].

science.energy.gov/ber/

**3. Cellulose structure**

about the cellulose synthase [20-21].


**Table 1.** Worldwide annual production of biomass

Minor components are proteins, lipids, pectin, soluble sugars and minerals (Table 2) [9]. It has a thickness of ~0.1 a 10 µm contrasting with <0.01 µm of cell membrane formed by pro‐ teins and phospholipids [18].

Examples of such biomass are angiosperms (hardwoods), gymnosperms (softwoods) and graminaceous plants (grasses such as wheat, giant reed and *Miscanthus*).

**Figure 1.** Structural organization of the plant cell wall. Cellulose is protected of degradation by hemicelluloses and lignin. Source: Office of Biological and Environmental Research of the U.S. Department of Energy Office of Science. science.energy.gov/ber/

Cell walls should play a wide array of disparate and sometimes opposing roles: the resist‐ ance to mechanical stress is necessary as well as the shape of the cell and protection against pathogens; at the same time, besides it must be reasonably flexible to withstand shear forces, and permeable enough to allow the passage of signalling molecules into the cell [19].
