Through which process does the body break down starch?

Expert Answers

An illustration of the letter 'A' in a speech bubbles

Starch is a polymer known as a polysaccharide. It is constructed of a long chain of glucose monomers joined together. Plants store excess glucose as starch in plastids until such time as it is needed as an energy source. Starch can also be consumed by heterotrophs and broken down to...

See
This Answer Now

Start your subscription to unlock this answer and thousands more. Enjoy eNotes ad-free and cancel anytime.

Start your Subscription

Starch is a polymer known as a polysaccharide. It is constructed of a long chain of glucose monomers joined together. Plants store excess glucose as starch in plastids until such time as it is needed as an energy source. Starch can also be consumed by heterotrophs and broken down to glucose which can be used as an energy source for cellular respiration to produce ATP.

The process by which starch is broken down is called hydrolysis or digestion. Enzymes specific to starch digestion (amylases) are found in the saliva as well as in the small intestine. These catalyze digestion of large starch molecules into simpler glucose monomers.

The process works by the addition of water which acts on the glycosidic linkages between adjacent sugars that are connected in the starch molecule. As water is added, the covalent bond connecting adjacent sugars is broken and the individual sugars are released. The glucose monomers of starch are joined by 1,4 glycosidic linkages which means that the number 1 carbon is connected to the number 4 carbon in two neighboring sugars.

Hydrolysis helps to break the covalent bond between the monomers in starch. By addition of water, a hydrogen atom from the water attaches to one monomer while the hydroxyl (OH) group attaches to the adjacent monomer. Once starch is completely hydrolyzed, the glucose monomers can easily be absorbed by the small intestine into the bloodstream and eventually will be transported to the body cells to use as an energy source.

I have included a link showing a 1,4 glycosidic bond between two glucose molecules. The second link has a diagram of a hydrolysis reaction.

 

Approved by eNotes Editorial Team
An illustration of the letter 'A' in a speech bubbles

The initial breakdown of starch occurs in your mouth by the enzyme called amylase. Amylase is secreted by the salivary glands. It catalyzes the hydrolysis of starch into smaller sugar subunits called monosaccharides. Glucose is the monosaccharide that makes up starch. The glucose is then transported to the digestive system and utilized by cells.

Cellular respiration is the process by which the sugar called glucose is used within an organism. Cellular respiration occurs in the mitochondria of eukaryotic cells. There are three main phases of cellular respiration. Each phase utilizes a different part of the mitochondria. Overall, cellular respiration is the process by which glucose and oxygen are used to make carbon dioxide, water, and adenosine triphosphate (ATP). Adenosine triphosphate is an energy source utilized by cells.

Approved by eNotes Editorial Team