Download Chemical Digestion and Enzymes

Chemical Digestion and Enzymes
The major nutrients taken in by the body through eating are carbohydrates, proteins, fats and nucleic acids.
These large macromolecules need to be broken down by the digestive system into their simpler building blocks.
In order to breakdown these nutrient they under go a chemical reaction called HYDROLYSIS. Hydrolysis is the
use of water to break the bonds between the monomers (building blocks) of the macromolecules.
Hydrolysis is a slow reaction and needs to be sped up. The body solves this problem by making a biological
catalyst called enzymes. Enzymes are special proteins produced by the cell. Enzymes break the bonds between
monomers at very specific locations (linkages).
Enzymes often require special conditions in order to act
i)
ii)
iii)
iv)
some work best in an acidic environment
(i.e. pepsin in the stomach)
other work in a neutral or alkaline (basic) environment
(i.e.. the digestive enzymes in the small intestine)
enzymes are affected by temperature changes
(i.e. higher temperatures will denature the enzyme so that it is no longer functional)
in order for the enzyme to function properly it may require the presence of metallic ions
(i.e. cobalt and magnesium), vitamins, or coenzymes in order to function properly.
There are three groupings of enzymes that are formed by secretory cells and then secreted into the digestive
tract.
Macromolecule
carbohydrates
proteins
fats
Enzyme
Carbohydrases
Proteases
Lipases
Monomers
monosaccharides (glucose, galactose, fructose)
amino acids
glycerol + 3 fatty acids
Digestive Enzymes
Most of the digestive enzyme names start with the name of the substrate they react on
and have the ending "ase" added.
Example: maltose is broken down by an enzyme called maltase.
Some enzymes still use their older names such as pepsin.
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A Summary of Chemical Digestion
In humans and other mammals, chemical digestion begins in
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Salivary glands release the enzyme called salivary amylase,
Amylase breaks down starch into smaller disaccharide sugar molecules
stomach
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gastric juice secreted by the stomach contains hydrochloric acid and the enzyme, pepsin.
Pepsin
begins the breakdown of protein in the stomach
Pepsin functions well within a pH range of 1 to 2.
duodenum
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is 25 cm long
secretes enzymes from its lining,
the pancreas and liver both empty their enzymes into the duodenum to complete the process
of digestion.
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Pancreatic juice is alkaline and thus neutralizes the acidity of partially digested food coming
from the stomach, stopping any further action of pepsin
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produces no enzymes
water is absorbed from indigestible material through its walls
anaerobic bacteria living there,
digest some of this material, and some of it is absorbed for use by the body
synthesize some B vitamins and Vitamin K which is then used by the body.
The total digestion of a large meal takes about 24-33 h
mouth
pancreas
Large
intestine
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The Regulation of Digestive Secretions
The secretion of digestive enzymes is regulated by both nerves and hormones.
A hormone is a chemical regulator that is secreted in one part of the body and transported by the bloodstream
to another part, where it causes a response.
Examples
a) Secretion of Gastric Juices
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Nerve impulse stimulates the lower part of the stomach to produce the hormone gastrin
Gasterin enters the circulatory system and is carried back to the upper part of the stomach
Gasterin then stimulates the digestive glands lining the walls of the upper part of the stomach to
secrete mucin pepsin, hydrochloric acid, lipases.
b) Neutralization of Chyme
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Chyme entering the duodenum stimulates the glands of the duodenum to secrete the hormone
secretin into the bloodstream
Secretin stimulates the duct cells of the pancreas to release an alkaline fluid containing sodium
carbonate and sodium bicarbonate into the duodenum which changes the pH from 2 to 8
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c) The hormone secretin and cholecystokinin (CCK) are secreted by the duodenum and stimulates the
pancreas to release its digestive enzymes into the duodenum. These enzymes also stimulate the gall
bladder to secrete bile salt.
Enzymes of the Human Digestive System
Place where
enzyme acts
Substrate
Enzyme
mouth
starch,
glycogen
salivary amylase
stomach
protein
fats
fats
peptides
peptides
peptides
starch
small
intestine
ribonucleic acid
deoxyribonucleic acid
peptides
tripeptides
maltose
sucrose
lactose
pepsin
lipase
pancreatic lipase
trypsin
chymotrypsin
carboxypeptidase
pancreatic amylase
ribonuclease
deoxyribonuclease
aminopeptidase
tripeptidase
maltase
sucrase
lactase
Products
Origin of
Enzyme
maltose
salivary
glands
peptides
stomach
glands
glycerol + 3 fatty acids
glycerol + 3 fatty acids
simpler peptides
simpler peptides
simpler peptides
pancreas
maltose
ribonucleotides
deoxyribonucleotides
simpler peptides
dipeptide + amino acid
glands in the
walls of the
small intestine
glucose + glucose
glucose + fructose
intestinal
glands
glucose + galactose
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The Roles of Related Organs
Three other organs associated with the digestive tract are the liver, gall bladder, and pancreas.
These organs play vital roles in the digestive process.
The Liver
The liver is the largest organ in the body and has been identified as having over 500 different functions that are
essential to the body's general good health.
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produces bile salts from cholesterol which is released into the small intestine to emulsify fat globules
(break up ) to allow lipase to chemical break the fat up into glycerol and fatty acids
breaks down old red blood corpuscles, and hemoglobin
the decomposed hemoglobin molecules are used to make bile salts.
the liver collects from the bloodstream chemicals that are in excess of the amount needed by the body at
any given time.
The liver converts and stores all monosaccharides (except glucose), into glycogen
The liver will convert the stored glycogen back into glucose when the glucose level in the bloodstream
become low
The liver also stores fat-soluble vitamins A, D, E, and K
the liver works to detoxify various poisons ingested with food and drink in addition to those produced in
the intestines.
The liver is highly evolved organ that performs a wide range of important, specialized functions for the body.
The Gall Bladder
The gall bladder serves as the
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storage warehouse for bile produced in the liver.
bile contains a number of chemicals that include cholesterol
bile salts are used in fat digestion
bile salts are reabsorbed by the small intestine and is carried back to the liver to be recycled back into
bile
The Pancreas
The pancreas is the source of
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several enzymes that act on carbohydrates, fats, and peptides (smaller segments of proteins)
produces and releases a basic solution that changes the pH of chyme (from a strongly acid mixture to
a weakly basic one) after it enters the duodenum.
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