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Nutrition (Chapter 3)
Need for food:
Food is required for energy, for the growth and repair of cells and to make chemicals for metabolic
reactions occurring in the body.
The 6 common elements found in food are:
The 5 elements present in dissolved salts are:
Carbon (C)
Hydrogen (h)
Nitrogen (N)
Oxygen (O)
Phosphorus (P)
Sulfur (S)
Sodium (Na)
Magnesium (Mg)
Chlorine (Cl)
Potassium (K)
Calcium (Ca)
The 3 trace elements (only found in small amounts in organisms) are:
Iron (Fe)
Copper (Cu)
Zinc (Zn
Biomolecules
 Biomolecules are chemicals that are made inside a living thing.
 The 4 main types of biomolecules found in food are:
Carbohydrates, Lipids (fats, oils), Proteins, Vitamins
 When elements are combined in certain ratios, they form simple biomolecular units.
 The ratio for all carbohydrates = Cx(H2O)y Example: Formula for glucose = C6H12O6 (x = 6, y = 6)
Carbohydrates
Elements in carbohydrates: carbon, hydrogen, oxygen
3 main types of carbohydrates: monosaccharides, disaccharides,
polysaccharides
Monosaccharides
Monosaccharide: a carbohydrate made up of a single sugar unit.
Examples: glucose (fruit, sweets, soft drinks), fructose (fruit)
Disaccharides
Disaccharide: a carbohydrate made up of two sugar units.
Examples:
sucrose = glucose + fructose (table sugar)
Maltose = glucose + fructose (in germinating seeds)
Lactose = glucose + galactose (milk)
Monosaccharide
(glucose)
Disaccharide
(maltose)
Polysaccharide
(starch)
Polysaccharides
Polysaccharide: a carbohydrate made up of many sugar units
Examples: starch, cellulose, glycogen
Starch = many glucose molecules joined together (rice, potatoes, bread, pasta)
Function of starch: to provide energy
Starch is a carbohydrate stored by plants
Cellulose = many glucose molecules joined together (plants)
Function: Important structural function in plants - it is a component of plant cell walls.
Glycogen = many glucose molecules
Function: stored by animals (many in liver and muscles) and can be used for energy
Metabolic Function of Carbohydrates: to provide a source of energy for metabolic activity
Structural function: Cellulose is an important component of plant cell walls
Lipids
 Elements in lipids: carbon, hydrogen, oxygen (no simple ratio, like carbs)
Fats & Oils:
 Fats: are lipids that are solid at room temperature.
 Oils: are lipids that are liquid at room temperature
Sources: butter, olive/sunflower oil, cream, margarine
Structure of Lipids: Lipids are composed of glycerol molecules attached to fatty acid molecules. The
smallest lipid, a triglyceride, contains one glycerol molecule attached to 3 fatty acids.
Phospholipids: Phospholipids are lipid-like substances, where one of the fatty acids is replaced by a
phosphate group or has a phosphate group attached.
Structure of a Phospholipid
Phosphate
Metabolic function of lipids: to provide a source of energy for metabolic activity
Structural Function: component of cell membranes
Proteins
 Elements in Proteins: carbon, hydrogen, oxygen and nitrogen (also sometimes contain small amounts
of sulfur, phosphorous) no simple ratio




Structure: Proteins are composed of small units called amino acids.
Peptide = small chain of up to 20 amino acids
Polypeptide = chain of more than 20 amino acids
Protein = long polypeptide
Primary structure of a protein
aa
aa
aa
aa
aa
aa
peptide bonds
Sources: lean meat, fish, eggs, nuts, peas, beans
 The function of protein is very dependent on their 3D shape and the way in which they are folded.
 Fibrous proteins: show little or no folding. e.g. keratin, myosin
 Globular proteins: show lots of folding. e.g. albumen, enzymes
Metabolic Functions: Proteins are used to make enzymes, which control metabolic reactions.
(Enzymes are proteins which speed up chemical reactions)
Hormones are also proteins. Like enzymes, they regulate metabolic activity.
Structural function: fibrous proteins have a structural function for example: keratin is a component
of hair and skin & myosin is a component of muscles
Vitamins
Some vitamins are water-soluble and some are fat-soluble.
Water soluble – Example: Vitamin C
Function: tissue growth, cell production and to maintain good health
Sources: citrus fruits, such as oranges and lemons
Deficiency disease: Scurvy (soft gums and loose teeth)
Fat soluble – Example: Vitamin D
Function: tissue growth, cell production and to maintain good health
Sources: cod liver oil, egg yolk, dairy products
Deficiency disease: Rickets (bones do not form properly)
Minerals
Minerals are needed by plants and animals in small amounts.
Plants:
Calcium – helps bind cell walls together (absorbs from soil)
Magnesium – part of the structure of chlorophyll (absorbs from soil)
Animals:
Calcium – forms bones and teeth (dairy products)
Iron – required for healthy red blood cells, forms haemoglobin (red meat, green veg)
Water
The human body is about 60% water. Water is very important for living organisms for a number of
reasons:
(1) Water has an important structural function, it is a component of cytoplasm and body fluids.
(2) Water is a good solvent. Many substances in the body can dissolve in water, so it provides a
medium for chemical reactions to take place in.
(3) Water can easily move through membranes in the body and helps to transport many chemicals
around the body.
(4) It plays a direct role in many chemical reactions. Examples: respiration, photosynthesis
(5) It is a good heat absorber. This helps maintain fairly constant body temperature.
Metabolism
Anabolic Reaction: a reaction in which simple molecules are built up into more complex molecules.
Energy is required for anabolic reactions.
Example: Photosynthesis
Carbon dioxide
6CO2
+
Water
6H2O
Sunlight Energy
Glucose
C6H12O6
+
+
Oxygen
6O2
Catabolic Reaction: a reaction in which a complex molecule is broken down into simpler molecules.
Energy is released during a catabolic reaction.
Example: Respiration
Glucose
C6H12O6
+
Oxygen
6O2
Carbon dioxide
6CO2
+
Water
6H2O
+
Energy