DIGESTION OF CARBOHYDRATE,
PROTEIN, AND FAT
Biology 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 (1015%)
 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

DIGESTION OF LIPIDS
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.
