Topic 6.1

6.1.1: Why digest large food molecules?

Why digest food?

6.1.2: Why the need for enzymes?

Enzymes are proteins that serve as biological catalysts. They speed up the rate of reaction, at body temperature, without being changed into a different molecule during the process. It is important to remember that an enzyme will act on a specific substrate, such as, proteases break down proteins, carbohydrases break down carbohydrates, lipases break down lipids, and nucleases breakdown nucleic acids. Without enzymes the break down of food molecules small enough for absorption by the body occurs too slowly.

Enzyme digestion

6.1.3: Amylase, protease and lipase

The table below outlines the source, substrate, products and optimum pH for one amylase, one protease and one lipase.

Enzyme Source Substrate Products Optimum pH
Salivary amylase salivary glands starch maltose 7.0
Pepsin stomach wall proteins small polypeptides 1.5 - 2.0
Pancreatic lipase pancreas triglycerides (fats and oils) fatty acids and glycerol 7.0

6.1.4 & 6.1.5: The human digestive system

The human digestive system consists of an alimentary canal and associated accessory glands. The main parts to identify in the figure below include the mouth, esophagus, stomach, small intestine, large intestine and anus along with the digestive glands - liver and pancreas. Also include the gall bladder. Make note of the interconnections between these structures the functions of the stomach, small intestine and large intestine.

Enzyme digestion

6.1.6 & 6.1.7: Villus structure

Absorption is the process by which the nutrients of food move from the small intestine into the bloodstream. It requires the digestion of food into monomers that are small enough to pass across cell membranes. The structure of the villus is related to its role in the absorption and the transport of the products of digestion. The figure below illustrates how its structure is relation to its function. Assimilation is the building of polymers using monomers. Fat monomers are assimilated in epithelial cells; glycogen is assimilated in liver cells, amino acids are assimilated in all cell types.

Enzyme digestion

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