ENERGY IN FOOD
Digestive System
Enzymes/pH
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Food and Energy
• Organisms must obtain energy to carry out life
processes
• Amount of energy in food is measured in Calories
• Food also contains the raw materials (nutrients)
used to build/ repair body tissues
• Nutrients supplied by food:
Water Carbohydrates Lipids (fats)
Proteins Vitamins
Minerals
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Function of the Digestive System
• Breaks up food physically & chemically
• Stores food for a short time
• Absorbs digested foods and passes them into the
circulatory system
• Stores and eliminates undigested food from the
body
• Types of Digestion
1. Mechanical: The physical breakdown of food by
non-enzyme means
2. Chemical: The use of enzymes to breakdown food
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Function of the Digestive System, cont.
• Consumers must be able to break down food into
molecules that can be absorbed and used by cells
• In many multicellular organisms, this is accomplished
by a digestive system
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Enzymes and Digestion
• Enzyme – specialized proteins that act as biological
catalysts
• Catalyst – substance that speeds up chemical
reactions and remains unchanged by the reaction
• All the activities of living things are controlled by
chemical reactions
• Without enzymes, these reactions would happen too
slowly or require so much activation energy that the
organism would die
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Enzymes and Digestion, cont.
• Activation energy – amount of energy needed to get
a chemical reaction started
• Chemical reaction – the breaking down and/or
forming of new compounds
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Enzymes…
• Are: a three dimensional protein
• Have: a specific area that attaches to the chemical
compound undergoing change (active site)
• Fit: like a puzzle piece to one type of compound
(substrate)
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Enzymes…
• Need: specific pH range
• Require: constant body temp (Humans – 98.6o F)
 high temperatures denature (change shape) of
enzymes
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Enzyme-Substrate Complex
• When the enzyme binds with its substrate, changes
occur in the enzyme at the active site
• This alteration of the active site is called induced fit
• Induced fit enhances the enzyme’s ability to break
down the substrate
• If the enzyme is missing or damaged, the reaction
cannot happen
• Example: lactose intolerance
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Enzyme Inhibition
Inhibition – keeping something from working correctly
• Competitive Inhibitors:
Chemicals that resemble
and enzyme’s normal
substrate and compete for
the active site
• Allosteric Inhibitors:
Chemicals that do not bond
to active site but to another
part of enzyme; changes
enzyme shape
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Organs of the Digestive System
• Digestion begins in the mouth with:
1. Mechanical - teeth & tongue chop/mix the food
2. Chemical - salivary glands add amylase to break
down starches into simple sugars
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Organs of the Digestive System, cont.
• Pharynx – located at back of throat; opening for
tubes that lead to 2 systems
1. Respiratory – trachea
2. Digestive – esophagus
• Epiglottis – flap of tissue that covers opening to tube
not being used
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Organs of the Digestive System, cont.
• After swallowing, food moves down the esophagus to
the stomach
• The food is moved in a one-way direction by smooth
muscle contractions (peristalsis)
• The Stomach:
1. Digests mechanically & chemically
2. Has pH of 2
3. Secretes enzyme pepsin (acts on proteins)
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Organs of the Digestive System, cont.
After ~ 2 hours the food
leaves the stomach and
enters
The Small Intestine:
• 7 meters long – 2.5 to 3
cm diameter
• Most chemical digestion
and absorption of
nutrients occurs here
• Digestion of carbs ,
proteins, lipids and
nucleic acids
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Organs of the Digestive System, cont.
• Accessory Organs of Small Intestine:
Pancreas
Liver
Gall Bladder
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Organs of the Digestive System, cont.
• After 4-6 hours what is left of your meal leaves your
small intestine and enters
The Large Intestine
• ~ 1.5 meters long
• 3 sections – cecum, colon and rectum
• Absorbs water & salts from the undigested material
• Colonies of E. coli will produce vitamin K (for blood
clotting) and other compounds needed to complete
digestion.
• Solid waste stored in rectum & excreted through
anus
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Organs of the Digestive System, cont.
• Lining of Small Intestine:
The small intestine is folded into fingerlike
projections called villi
The villi are covered in even smaller projections
called microvilli
These structures increase the total surface area over
which nutrients can be absorbed into the blood
stream
• The small and large intestines have an extensive
supply of capillaries; this allows the digested
nutrients to easily enter the circulatory system
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