Question

Describe in sequence the digestion of proteins in the various regions of the alimentary canal in human beings. How are the end products of protein digestion absorbed into the body?

Answer 1

Proteins:

1. Proteins are the major biomolecules needed by the body to function.
2. They are made up of repeating units called amino acids held together by peptide bonds.
3. During digestion, proteins are broken down into amino acids through hydrolysis.
4. The amino acids can dissolve in the blood and are transported to tissues and organs.
5. Body requires amino acid supplements to build up proteins.
6. Amino acids are of two types namely, essential and nonessential amino acids.
7. Essential amino acids cannot be synthesized by the body and it has to be taken via food.
8. Non-essential amino acids can be synthesized by the body and need not be supplemented in food.

Protein digestion in humans:

1. Digestion is the biochemical process by which food is broken down and converted to energy.
2. Digestion of proteins takes place in the stomach.
3. When the food enters the stomach, it mixes with the HCl and the enzyme pepsin secreted by the cells of the stomach that initiate the breakdown of proteins.
4. Pepsin breaks down the peptide bonds.
5. The pancreatic enzymes trypsin, chymotrypsin, and carboxypeptidase break down the polypeptides and result in smaller units called peptides.
6. Intestinal juice released in the small intestine also contains several digestive enzymes that act on the peptide bonds.
7. The end product of protein digestion in the small intestines is amino acids.
8. Amino acids are then absorbed by an active absorption process.
9. It occurs either by a carrier transport mechanism.

Enzymes involved in protein digestion:

1. The enzyme pepsin plays an important role in the digestion of proteins by breaking down the intact protein to peptides.
2. The enzymes included are pepsin, trypsin and chymotrypsin.
3. Pepsin converts proteins into peptones.
4. Trypsin and chymotrypsin convert peptones into polypeptides.
5. Trypsin cleaves the peptide bonds with basic amino acids and chymotrypsin cleaves the peptide bonds with aromatic amino acids.
6. Specifically, carboxypeptidase, dipeptidase, and aminopeptidase play important roles in reducing the peptides to free amino acids.
7. The amino acids are absorbed into the bloodstream through the small intestines.

Enzyme	Site of Action	Substrate	End Product
Pepsin	Stomach	Proteins	Peptides
Trypsin	Small intestine	Proteins	Peptides
Elastase	Small intestine	Proteins	Peptides
Chymotrypsin	Small intestine	Proteins	Peptides
Carboxypeptidase	Small intestine	Peptides	Amino acids and peptides
Aminopeptidase	Small intestine	Peptides	Amino acids
Dipeptidase	Small intestine	Peptides	Amino acids