Digestive Enzymes
Production
Location
Action
Main Function of Enzymes
• 'Digestive enzymes' are enzymes (biological
catalysts) that break down polymeric
macromolecules into their smaller building blocks,
in order to facilitate their absorption by the body.
• Digestive enzymes are found in the digestive tract
of animals (including humans) where they aid in
the chemical digestion of food
• Enzymes are large quaternary proteins that
function by lowering the activation energy
required for a reaction to take place - essentially
speeding them up.
Enzyme Function
• In the digestive system the reaction that is
catalyzed repeatedly is a hydrolysis reaction
(splitting by adding water)
• The polymers polypeptides, polysaccharides
and lipid molecules have bonds broken at
specific locations by specific enzymes.
• The purpose is to reduce these
macromolecules into their simplest building
blocks - monomers so that they can be
absorbed
Lock and Key Model
• Enzymes have specific 3-D shapes that allow
certain substrate molecules to fit into their
active site so that the reaction can be
catalyzed
Enzyme Production
• Digestive enzymes are diverse and are found in:
• The saliva secreted by the salivary glands,
• in the stomach secreted by cells lining the
stomach,
• in the pancreatic juice secreted by pancreatic
exocrine cells,
• and in the secretions of the small intestine, or as
part of the lining of the gastrointestinal tract.
Enzymes by location
• Mouth
• lingual lipase: Lipid digestion initiates in the
mouth. Lingual lipase starts the digestion of the
lipids/fats.
• amylase: Carbohydrate digestion also initiates in
the mouth. Amylase produced by the salivary
glands breaks complex carbohydrates to smaller
chains, or even simple sugars. It is sometimes
referred to as ptyalin.
Stomach
• The enzymes that are secreted in the stomach are called
gastric enzymes.
• Pepsinogen is the main gastric enzyme. It is produced by
the stomach cells in its inactive form pepsinogen
• Pepsinogen is then activated by the stomach acid into its
active form, pepsin.
• Pepsin breaks down the protein in the food into smaller
particles, such as polypeptides and amino acids. Protein
digestion, therefore, first starts in the stomach.
Pancreas
Trypsinogen is an inactive(zymogenic) protease that, once
activated in the duodenum, into trypsin, breaks down
proteins at the basic amino acids. Trypsinogen is
activated via the duodenal enzyme enterokinase into its
active form trypsin.
Chymotrypsinogen, which is a inactive(zymogenic)
protease that, once activated by duodenal enterokinase,
into chymotrypsin breaks down proteins at their
aromatic amino acids. It can also be activated by trypsin.
Carboxypeptidase is a protease that takes off the terminal
amino acid group from a protein
Pancreatic enzymes continued
Several elastases that degrade the protein elastin and
some other proteins.
Pancreatic lipase that degrades triglycerides into fatty
acids and glycerol.
Cholesterol esterase that degrades cholesteral
Phospholipase that degrades phospholipids
Several nucleases like DNAase and RNAase that
degrade nucleic acids into nucleotides
And further still….
Pancreatic amylase that breaks down, besides starch
and glycogen, most other carbohydrates.
Humans lack the enzyme to digest the carbohydrate
cellulose, mainly due to its special hydrogenbonding structure (really strong).
Small Intestine
• Throughout the lining of the small intestine there are numerous
"brush border" enzymes whose function is to further cleave the
already-broken-down products of digestion into absorbable
particles. Some of these enzymes include:
• Sucrase:
breakdown sucrose into glucose and fructose
• Lactase:
breakdown lactose into glucose and galactose
• Maltase
breakdown lactose into glucose and glucose
• Breakdown of Disaccharides into Monosaccharides!!
Chemical Digestion completed
• And that does it - macromolecules broken down
into their basic building block units:
• monosaccharides,
• amino acids,
• glycerol and fatty acids,
• and nucleotides
• (vitamins and minerals are already done)