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The Digestive System
Part I
The Chemistry of Life
The Chemistry of Life
Questions for Consideration
1. List the 5 nutrients required to maintain good health;
2. List two ways the body uses:a) Lipids
b) Proteins
c) Carbohydrates
d) Vitamins
e) Minerals
3. List some foods that are mainly carbohydrates.
4. List some foods that are mainly fats.
5. Are fats good or bad for you? Justify your answer.
Chemistry of Life
The Chemistry of Life
In order to fully understand the digestive system you must have a
good understanding of both biology (anatomy) and chemistry.
Biochemistry
Chemistry of Life
• Food can be classified into 3 nutrient types:
1.Carbohydrates
2.Proteins
3.Fats (also called lipids)
Chemistry of Life
Carbohydrates• The body’s most important source of energy;• The largest component of our regular diet ;• Sources of carbohydrates include:
• potatoes, • rice,• corn, • bread, • pasta and • Many fruits (high sugar content)
Chemistry of Life
Carbohydrates• Carbohydrates are made of either single sugar molecules
or chains of sugar molecules.
• Saccharide = Greek word meaning “sugar”
• Monosaccarides = a carbohydrate made of only 1 sugar molecule
• Disaccharides = carbohydrates made of 2 sugar molecules
Chemistry of Life
Carbohydrates• Monosaccarides = a carbohydrate made of only 1 sugar
molecule (e.g. Glucose and fructose)
• Sugars are made of carbon, oxygen and hydrogen
• Glucose • The simplest sugar
• C6H12O6
Most sugars end in “ose”
Chemistry of Life
Carbohydrates• Fructose = a sugar found in fruit
• Lactose = a sugar found in milk
• Maltose = a sugar found in beer
• Sucrose = table sugar (made of glucose + fructose)
Chemistry of Life
Complex Carbohydrates• Carbohydrates made up of many sugar molecules linked in
long chains.
• Starch = 2000 - 6000 glucose molecules
• Excess sugars are usually stored as starches by plants. When a plant needs energy it breaks down a starch molecule into individual glucose molecules.
Wheat products (such as bread and pasta are rich sources of starches.
Chemistry of Life
Complex Carbohydrates• Cellulose
• A polysaccaride that makes up the cell walls of plants.• Often called fiber or roughage in our diet• Indigestible• Holds water in our large intestine and helps to eliminate wastes
Chemistry of Life
Checking Your Understanding
1) What is the difference between a monosaccaride, a
disaccaride and a polysaccharide?
2) What is the difference between gluose, sucrose and
starch?
3) What is the difference between starch and cellulose?
4) What is the primary purpose of carbohydrates in our diet?
Chemistry of Life
Lipids• Lipids can be divided into 3 groups:
1. Fats, oils and waxes;
2. Phospholipids;
3. Steroids
• Lipids are also storage compounds for energy (like carbohydrates)
• One gram of lipid contains 2x as much energy as 1 g of carbohydrate
Chemistry of Life
Lipids
• What lipids do in the body:
• absorption of vitamins,
• insulate the body,
• a major component of cell membranes,
• protect and cushion the organs of the body,
• are building blocks for hormones.
Chemistry of Life
Unsaturated vs. Saturated Fats• Saturated fats = contain no double bonds and the
maximum number of hydrogen atoms• Saturated fats are often solid (like butters and lard)
• Animal fats are usually saturated
• Unsaturated fats = contain one or more double bonds and therefore are missing hydrogen atoms.• Unsaturated fats are often very soft or liquids (oils)• Many plant fats are unsaturated.
Chemistry of Life
Chemistry of Life
Hydrogenation of Fats
Unsaturated fats (like plant fats) can be made more solid by adding hydrogen atoms.
Margarine is an example
of a hydrogenated fat.
Chemistry of Life
Checking Your Understanding #2
1) What are fats?
2) Name the three groups of lipids.
3) What is the difference between saturated and unsaturated
fats?
4) What is hydrogenation? What is the result of
hydrogenation?
Chemistry of Life
Proteins
• Proteins are used to build cellular structures;
• Proteins are used in chemical activities;
• Enzymes are proteins that control the rates of many
reactions (including digestion and cellular respiration).
• Proteins are NOT usually used for energy.
Chemistry of Life
Proteins• Proteins are made of carbon, oxygen, hydrogen and
NITROGEN (and sometimes sulfur).
• Proteins are made of 20 different amino acid building blocks.
• Small proteins may contain 8 amino acids, others contain more than 4000 amino acids.
• Polypeptide = a chain of several amino acids forming a protein.
Chemistry of Life
Proteins in our diet
• Our bodies can make most amino acids but there are 8 that our bodies can’t make – we must eat these.
• We call these 8 amino acids “Essential Amino Acids”
Chemistry of Life
Sources of Proteins in our diet
• Meats & Fish
• Beans
• Nuts & Seeds
• Dairy products
• Tofu
• Some Veggies
Chemistry of Life
Checking Your Understanding #3
1) What are proteins used for?
2) What are amino acids?
3) List some foods that are good sources of proteins?
Mini Quiz• Match the following structures with the correct nutrient:
1 A Simple Carbohydrate
2 B Lipid
3 C Protein
4 D Complex Carbohydrate
