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Nutrients & the
Digestive System
Four Stages of Processing Food
1. Ingestion: taking in and eating food
2. Digestion: breaking down food by
mechanical (chewing) and chemical
processes into smaller molecules
3. Absorption: transporting molecules from
digestive system to the circulatory system
4. Elimination: removal of undigested solid
waste from the body
Macromolecules-Nutrients
• Nutrients are required to perform life
functions and obtain energy for survival
4 Macromoleules:
• Carbohydrates
• Lipids
• Proteins
• Nucleic Acids
Micronutrients
• Vitamins
• Minerals
We also need . . .
•
WATER
•
FIBRE
Carbohydrates
Carbohydrates
•
Carbohydrates are a family of organic
molecules made up of carbon, hydrogen, and
oxygen atoms. Some are small, simple
molecules, while others form long polymers.
•
Carbohydrates have the general formula
(CH2O)x
• Primary function = short-term energy storage
• Provides energy for cellular respiration
Saccharide is derived from Greek meaning
“sweet”
• Monosaccharide: single sugar molecule
– Glucose: sugar found in blood
– Fructose: sugar found in fruit
Glucose
Fructose
• Disaccharide: two sugar molecules joined with
a glycosidic bond.
– Sucrose: table sugar
– Lactose: found in diary products
• Polysaccharide: many sugars linked together
– Starch: stores energy in plants
– Glycogen: stores energy in animals
– Cellulose: found in leaves of plants
• Suffix “ose” is used when naming simple sugars
(e.g., monosaccharides & disaccharides)
Carbohydrates
• Major source of energy
• Monosaccharides provide quick energy
because they do not have to be digested
• Disaccharides and polysaccharides have to be
digested
• Cellulose cannot be digested, therefore it
provides fibre or roughage in our diet
Lipids
Lipids
• Examples: fats, waxes, steroids, phospholipids
• Functions include:
– Long-term energy storage
– Fats cushion and protect organs and joints
– Fat under the skin helps insulate the body
– Steroids = hormones and cholesterol
– Phospholipids = cell membrane
Lipids
• Why are lipids stored by the body?
• Carbon-Hydrogen bonds are a very efficient
way of storing energy
• Lipids store more than twice the energy per
gram than carbohydrates
Proteins
Proteins
• Functions include:
– When embedded into cell membranes :
• help transport substances across membranes
– Give cells support and shape (i.e., cytoskeleton)
– Structure = muscle, skin, organs, hair
– Enzymes: acts as catalysts to speed up chemical
reactions in the cell
Proteins
• Structure
– Proteins are made of long chains of amino acids
– About 22 different Amino Acids
– 8 Amino Acids are considered ESSENTIAL and
must be obtained from the food we eat
Amino Acids
• Amino Acids are joined together peptide
bonds
• Therefore, chains of amino acids are called
polypeptides
• A single protein may be made up of several
polypeptide chains
Breaking Down Macromolecules:
Enzymes
• Before the body can use macromolecules,
they need to be broken down into molecules
small enough to be absorbed by the small
intestine.
• Enzymes are used to speed up the process of
chemically digesting macromolecules!
• This chemical break down is called hydrolysis
Hydrolysis Reaction
• A disaccharide is split into two
monosaccharides by a hydrolysis reaction
where one water molecule is added
Hydrolysis Reaction
Common Enzymes
• Amylase:
– Produced in the salivary glands
– Released into the mouth
– Breaks down polysaccharides
• Pancreatic lipase:
– Produced in the pancreas
– Released into the small intestines
– Breaks down lipids
Common Enzymes
• Pepsin:
– Produced in stomach glands
– Released into the stomach
– Breaks down proteins
Vitamins
• Cannot be used for energy
• Organic substances (C, H, O, N + other atoms)
– Vitamin A: vision
– Vitamin C: boosts immune system
• May act as co-enzymes
Minerals
• Cannot be used for energy
• Inorganic substances: Do not contain Carbon
• For example:
– Iron in hemoglobin of red blood cells
– Calcium in bones and teeth
– Sodium in muscle and nerve cells
– Potassium to regulate heart beat and nerve signals
– Iodine for thyroid (see salt)
– Trace elements (e.g., zinc, selenium)
Water
• One can go without food for several weeks,
but can only go without water for a few days
• Water is used for:
– Transporting nutrients
– Eliminating waste
– Lubricating joints
– Forming bodily fluids; blood & mucus
– Regulating body temerature; sweating
Fibre
• Roughage – cellulose (cannot be digested)
• Functions by aiding digestion
– Keeps digested food moist and soft
(thereby helping to prevent constipation)
– Physically scrubs digestive tract
(cleans and helps to remove toxins)
Homework
• Refer to Section 10.1
• Answer questions on page 410
• # 3, 5-7,9,10, 11,12