DIGESTION OF CARBOHYDRATE, PROTEIN, AND FATBiology 233

Exercise 10.2

DIGESTION OF CARBOHYDRATES Enzyme: Amylase Begins in the mouth

with the enzyme Salivary Amylase, which catalyzes the reactions that digest polysaccharides into smaller oligosaccharides.

The amylase is denatured in stomach because of acidity

DIGESTION OF CARBOHYDRATES

The remaining polysaccharides and oligosaccharides are digested in the small intestine with the help of many enzymes, including pancreatic amylase

DIGESTION OF CARBOHYDRATES

There are also enzymes associated with the enterocytes of the small intestine called brush border enzymes these include lactase Maltase sucrase

DIGESTION OF LIPIDS

Enzyme: Lipase Lingual lipase,

secreted by intrinsic salivary glands of the tongue, digests a small amount of fat while food is still in the mouth but becomes more active at the acidic pH of the stomach.

DIGESTION OF LIPIDS

Gastric lipase makes a larger contribution to fat digestion (10-15%)

Most fat digestion occurs in the small intestine through the action of pancreatic lipase

DIGESTION OF LIPIDS

Fat globules are emulsified by bile which is made in the liver and stored in the gall bladder.

The monoglycerides and fatty acids produced by lipase action aggregate to form spherical structures called micelles

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Newly made triglycerides are bound to carrier proteins, forming tiny particles called chylomicrons that are secreted into the lymphatic capillaries (lacteals) of the intestinal villi.

Unlike other products of digestion lipids enter the blood as polymers rather than monomers.

DIGESTION OF PROTEINS The inactive forms of

enzymes are called zymogens.

This is necessary to prevent the enzymes from digesting the cells that produced them.

In the stomach there is also a stable layer of mucus that is stuck to the epithelial surface which protects the stomach from damage from both the acid and pepsin.

DIGESTION OF PROTEINS

Protein digestion begins in the stomach with the enzyme pepsin.

It is secreted by the chief cells of the gastric glands in the form of pepsinogen.

HCL helps convert pepsinogen into the active enzyme pepsin

Digests less than 15% of ingested protein.

DIGESTION OF PROTEINS

Duodenum is also normally protected from the gastric acid by a layer of mucus.

There is also a release of alkaline pancreatic juice to neutralize the chyme.

Also alkaline juice from the duodenal glands

DIGESTION OF PROTEINS

The majority of the protein digestion occurs in the small intestine with pancreatic enzymes such as trypsin and chymotrypsin and the brush border enzymes such as carboxypeptidase, elastase and aminopeptidase

DIGESTION OF PROTEINS Trypsin is released

from the pancreas in the form of trypsinogen and is activated by enterokinase an enzyme secreted by the mucosa of the small intestine.

Trysin will then convert trypsinogen into more trypsin.

It is also chymotrypsinogen and procarboxypeptidase into their active forms

TODAY’S LAB

Follow the directions in your lab manuals Group 1 will digest carbohydrates Group 2 will digest proteins Group 3 will digest fats At the end of the experiments you will

explain to the class your group results. You will be responsible for the information on

the handout given in class.