Cellular Digestion: Monomers, Polymers, and Digestive Enzymes

Cellular Digestion: Monomers, Polymers, and Enzymes

Cells may absorb simple molecules (monomers). Monomers are scarce in nature. Typically, there are large molecules (polymers), where hundreds or thousands of simple molecules are joined together, forming foods. Digestion is a process where digestive enzymes break down the bonds between monomers, releasing free monomers. Digestive enzymes are specific to each polymer.

For example, amylase breaks down the links between glucose molecules in starch. Lipase separates fatty acids from glycerol in fats. Proteases break the links between amino acids in proteins, releasing them. The digestive system is essentially a tube. Food undergoes a series of transformations during its journey.

These actions are of two types: mechanical (food fragmentation, mixing, etc.) and chemical (digestive enzymes break down food, and other chemical substances aid enzyme action).

The Mouth and Initial Digestion

The mouth is the entry point for food. It has structures that prepare food:

• Teeth fragment food.
• Glands secrete saliva.
• Tongue moves and mixes everything.

Different types of teeth cut, tear, and grind food. From the mouth, food passes through the pharynx.

Pharynx and Esophagus

The pharynx is a passage for both the respiratory and digestive systems. The epiglottis prevents food from entering the respiratory tract. The pharynx leads to the esophagus, a tube about 25 cm long, which connects to the stomach through a muscular ring called a sphincter. The cardiac sphincter controls food intake.

Small and Large Intestines

The pyloric sphincter connects the stomach to the small intestine. The small intestine has three sections: duodenum, jejunum, and ileum. The ileum connects to the large intestine through the ileocecal valve. The large intestine has three parts: cecum, colon, and rectum.