1. Cellulose
Polysaccharides are carbohydrate polymers consisting of tens to hundreds to several thousand
monosaccharide units. All of the common polysaccharides contain glucose as the
monosaccharide unit. Polysaccharides are synthesized by plants, animals, and humans to be
stored for food, structural support, or metabolized for energy.
Cellulose:
The major component in the rigid cell walls in plants is cellulose. Cellulose is a linear
polysaccharide polymer with many glucose monosaccharide units. The acetal linkage
is beta which makes it different from starch. This peculiar difference in acetal linkages results in
a major difference in digestibility in humans. Humans are unable to digest cellulose because the
appropriate enzymes to breakdown the beta acetal linkages are lacking. (More on enzyme
digestion in a later chapter.) Undigestible cellulose is the fiber which aids in the smooth working
of the intestinal tract.
Animals such as cows, horses, sheep, goats, and termites have symbiotic bacteria in the intestinal
tract. These symbiotic bacteria possess the necessary enzymes to digest cellulose in the GI tract.
They have the required enzymes for the breakdown or hydrolysis of the cellulose; the animals do
not, not even termites, have the correct enzymes. No vertebrate can digest cellulose directly.
Even though we cannot digest cellulose, we find many uses for it including: Wood for building;
paper products; cotton, linen, and rayon for clothes; nitrocellulose for explosives; cellulose
acetate for films.
The structure of cellulose consists of long polymer chains of glucose units connected by a beta
acetal linkage. The graphic on the left shows a very small portion of a cellulose chain. All of the
monomer units are beta-D-glucose, and all the beta acetal links connect C # 1 of one glucose to
C # 4 of the next glucose
CELLULOSE DIGESTION IN RUMINANTS
CELLULOSE DIGESTION
Cellulose make up the plant cell wall. Animals which depend on material e.g. leaves, wood have
to digest cellulose in order to release the cell contents required for the nutrition of the animals.
The enzyme which digest cellulose is called cellulase and it is not produced by most animals.
Some micro organisms take bacteria and protozoans can produce cellulase. However animals
which digest cellulose contain micro organisms in their gut which produce cellulose enzyme.
This is a symbiotic relationship.
CELLULOSE DIGESTION IN RUMINANTS
Ruminants are animals which chew the cud. Cud is un chewed grass taken into the rumen which
is returned to the mouth for chewing (regurgitation). Examples include Goats, Sheep, Cattle,
Antelopes and Buffalos. They have a complicated stomach consisting of four chambers.
2. Mouth. There is no enzyme secretion in the mouth so only mastication and Softening of food
occurs. Movement of food in the oesophagus is by Peristalsis.
Rumen. This is the largest component of the stomach where food is stored temporarily before
returning to the mouth for chewing. The food is return to the mouth by anti peristalsis. The
ruminant then lies down quietly and chews the cud. When the food is sufficiently chewed it is
swallowed and passed into the reticulum.
Reticulum. Bacteria action continues. It also separates finely ground material from course ones
and then retains and hard pieces of wood.
Omasum. Consists of parallel leaf like compartments with rough surfaces. The food is ground
finely. Absorption of water takes place at this region
Abomasum. Also called the true stomach. Enzymatic action of proteins takes place here.
Beyond this point digestion takes place like in man.
Other animals like termites eat wood, dry leaves etc which also contain cellulose. The digestion
of cellulose in termites is also done by cellulase enzyme produced by protozoans which live
symbiotically with the termites. The products of cellulose digestion may be glucose or acetic
acid in other animals.
