Why can we digest starch but not cellulose?

Answer 1

A specific enzyme catalyzes only a specific substrate. Another name for starch is "amylose". So amylase catalyzes amylose. Just like lactase catalyzes lactose. For people who are lactose intolerant, their bodies don't, or in small quantities, produce lactase, so it doesn't get digested. So, only the enzyme "cellulase" will catalyze the hydrolysis of "cellulose".

Answer 2

there is a difference between alpha and beta startches. cellulose is alpha linked, making it much more stable and more difficult to break down. startches that amylose breaks down quickly are beta linked, a much easier bond to break.

Answer 3

Enzymes are chemicals (proteins) that are directed towards a specific function.All enzymes are unique.Only a specific enzyme with a specific substrate will create a reaction. Cellulose is the most abundant polymer on earth but only a few organisms have the enzyme to break down cellulose.

Answer 4

Humans, with animal metabolism, can digest starch because we have the enzyme alpha-amylase to do the job.

Starch is a mixtures of glucans (polymers of glucose) that plants synthesize as their main food reserve, deposited in the cytoplasm of plant cells as insoluble granules of alpha-amylose (a linear polymer of several thousand glucose residues linked by alpha(1-4) bonds), and amylopectin (glucose residues linked by alpha(1-4) bonds and with alpha(1-6) branches every 24 to 30 glucose residues on average).

The enzyme alpha-amylase (present in saliva) randomly hydrolyzes all alpha(1-4) glucosidic bonds of starch (except those next to branches, and its outermost bonds). Once the chewed food reaches the stomach, acidic conditions of gastric juices inhibit the enzymatic activity of salivary alpha-amylase. However, by that time, starch has been reduced from several thousand to fewer than eight gluse units.

Starch digestion continues in small intestine by the action of pancreatic alpha-amylase and produces a mixture of maltose (a disaccharide of alpha(1-4) linked glucose residues), maltotriose (three glucose residues linkd by alpha(1-4) bonds), and dextrins (oligosaccharides with alpha(1-6) branches) that will be degrades into its monosaccharides by specific enzymes present in brush border membranes of the intestinal mucose (i.e., alpha-glucosidase, alpha-dextrinase or debranching enzyme, sucrase, and, at least in infants, a lactase.

Now, animal metabolism cannot metabolize cellulose because alpha-amylase, as the principal enzyme to metabolize starch, and the others that take place in the digestive tract, can hydrolize only glucoses linked with alpha bonds. Cellulose is a polymer of glucoses linked with beta bonds, this a tremendous impediment to alpha-amylase to digest cellulose. This enzymatic hydrolisis is given by microorganims.

Answer 5

The geometry of the bonds is different, and the shapes of enzyme active sites are highly specific.

Answer 6

starch is insoluble....

Answer 7

In a Bio-Catalytic manner.