Grade 12 digestive enzymes

Enzymes digest most macromolecules in food into monomers in the small intestine

Stomach Acids

The stomach contains gastric glands which release digestive acids to create a low pH environment (pH ~2)
The acidic environment functions to denature proteins and other macromolecules, aiding in their overall digestion
The stomach epithelium contains a mucous membrane which prevents the acids from damaging the gastric lining
The pancreas releases alkaline compounds (e.g. bicarbonate ions), which neutralise the acids as they enter the intestine

Bile

The liver produces a fluid called bile which is stored and concentrated within the gall bladder prior to release into the intestine
Bile contains bile salts which interact with fat globules and divide them into smaller droplets (emulsification)
The emulsification of fats increases the total surface area available for enzyme activity (lipase)

Enzymes

Enzymes are biological catalysts which speed up the rate of a chemical reaction (i.e. digestion) by lowering activation energy
Enzymes allow digestive processes to therefore occur at body temperatures and at sufficient speeds for survival requirements
Enzymes are specific for a substrate and so can allow digestion of certain molecules to occur independently in distinct locations

Carbohydrate digestion begins in the mouth with the release of amylase from the salivary glands (amylase = starch digestion)
Amylase is also secreted by the pancreas in order to continue carbohydrate digestion within the small intestine
Enzymes for disaccharide hydrolysis are often immobilised on the epithelial lining of the small intestine, near channel proteins
Humans do not possess an enzyme capable of digesting cellulose (cellulase) and hence it passes through the body undigested

The pancreas also releases nucleases which digest nucleic acids (DNA, RNA) into smaller nucleosides

Protein digestion begins in the stomach with the release of proteases that function optimally in an acidic pH (e.g. pepsin = pH 2)
Smaller polypeptide chains enter the small intestine where they are broken down by endopeptidases released by the pancreas
These endopeptidases work optimally in neutral environments (pH ~ 7) as the pancreas neutralises the acids in the intestine

Lipid breakdown occurs in the intestines, beginning with emulsification of fat globules by bile released from the gall bladder
The smaller fat droplets are then digested by lipases released from the pancreas

Amylase digests amylose into maltose subunits (disaccharide) and digests amylopectin into branched chains called dextrins

Both maltose and dextrin are digested by enzymes (maltase) which are fixed to the epithelial lining of the small intestine
The hydrolysis of maltose / dextrin results in the formation of glucose monomers

Starch is a polysaccharide composed of glucose monomers and accounts for ~ 60% of the carbohydrates consumed by humans

Starch can exist in one of two forms – linear chains (amylose) or branched chains (amylopectin)

The digestion of starch is initiated by salivary amylase in the mouth and continued by pancreatic amylase in the intestines

Starch digestion by amylase does not occur in the stomach as the pH is unsuitable for amylase activity (optimal pH ~ 7)

Glucose can be hydrolysed to produce ATP (cell respiration) or stored in animals as the polysaccharide glycogen

Glucose monomers can also be generated from the breakdown of other disaccharides (such as lactose and sucrose)

12.1 C Digestive Enzymes

Google Sites

Report abuse