Chapter 3: Nutrition
Leaving Certificate Biology
Higher Level
Function of Food
• Food is a complex of chemicals required
by a living organism to maintain
metabolism and continuity of life
Common Elements in Food
– Carbon
C
– Hydrogen
H
– Oxygen
O
– Nitrogen
N
– Phosphorus
P
– Sulphur
S
Elements in Food as
Dissolved Salts
• 5 elements present in dissolved salts:
– Sodium
Na
– Magnesium
Mg
– Calcium
Ca
– Potassium
K
– Chlorine
Cl
Trace minerals
• 3 trace elements (minerals) present in living organisms:
– Iron
Fe
– Copper
Cu
– Zinc
Zn
Biomolecules
• Biomolecules are chemicals found in and
produced by living organisms
• There are 4 major types of biomolecules:
– Carbohydrates
– Lipids
– Proteins
– Vitamins
Carbohydrates
• C, H, O: Ratio: Cx(H2O)y
• Three categories:
– Monosaccharides
– Disaccharides
– Polysaccharides (CH2O)n
Monosaccharides
 Glucose [C6H12O6] - a reducing sugar
and formed by breakdown of glycogen
 Fructose [C6H12O6] - a reducing sugar
and found in many fruits
 Galactose [C6H12O6] - a reducing sugar
and formed by breakdown of lactose
(found in milk)
Disaccharides
• Maltose (a reducing sugar)
– Found in germinating seeds (e.g. barley)
– Glucose + Glucose → Maltose [C12H22O11] + H2O
• Sucrose (NOT a reducing sugar)
– Commonly known as table sugar
– Glucose + Fructose → Sucrose [C12H22O11] + H2O
• Lactose (a reducing sugar)
– Found in milk - some people have lactose-intolerance
– Glucose + Galactose → Lactose [C12H22O11] + H2O
Polysaccharides
• Starch (also known as amylose)
– Plants store glucose as starch, e.g. potatoes, bananas
– Long chains and some branching of glucose molecules making it
easy to digest
• Cellulose (also known as fibre/roughage)
– Found in cell walls and stems of plants such as celery
– Composed of many glucose molecules bonded together in long
chains making it difficult to digest
• Glycogen
– Animals store glucose as glycogen in liver and muscles
– Glycogen is more branched than starch
Structural and Metabolic roles
of Carbohydrates
• Structural role:
– Cellulose: component of cell walls; keeps
plant upright
• Metabolic role:
– Energy: Mono-, Di-, and Polysaccharides
are metabolised to release energy
Lipids
• Lipids: consist of the elements C, H, and O, but
have fewer O atoms than carbohydrates
– Two main categories:
• Triglycerides
• Phospholipids
– Food sources of lipids:
• Butter, oils, margarines, cream, olives, animal fat
Triglycerides
• Triglycerides: one molecule of glycerol linked to
three fatty acid molecules
– Fats:
solid at room temperature (RT)
– Oils:
liquids at RT - contain different types of
fatty acids than fats
Fatty acid 1
Fig. 1:
A Triglyceride
Glycerol
Fatty acid 2
Fatty acid 3
Phospholipids
• Phospholipids: one fatty acid replaced by
a phosphate
Fig. 2:
A Phospholipid
P
Fatty acid 1
Glycerol
Fatty acid 2
Structural and Metabolic roles
of Lipids
• Structural role:
– Phospholipids: component of cell
membranes of all living cells
– Triglycerides: form adipose tissue that
surrounds important internal organs and
acts as a shock absorber
• Metabolic role:
– Energy: triglycerides are stored by
organisms as a source of energy
Proteins
• Proteins consist of elements: C, H, O, N - no
particular ratios
• Sulfur and phosphorus are also present in some proteins
• There are 20 common amino acids found in proteins
– Two main categories of protein:
• Fibrous proteins - little or no folding (e.g. proteins
found in hair, skin & nails)
• Globular proteins - lots of folding (e.g. protein
hormones, enzymes and antibodies)
Structural and Metabolic roles
of Proteins
• Structural role:
– Skin, nails and hair contain keratin
– Muscle composed of actin and myosin
– Bone, ligaments and tendons contain
collagen
• Metabolic role:
– Enzymes, antibodies and some hormones
are proteins
Vitamins
• Complex organic substances needed only in tiny
amounts
• Share no common chemical characteristics - all
chemically unique
• Identified by letters based on their chemical structure
• A, D, E, and K are fat-soluble vitamins
• B-group and C are water-soluble vitamins
1.3.6 Structural Role of Biomolecules
Vitamins
1. Structural role:
– Vitamins do not have any structural
role in living organisms
1.3.7 Metabolic Role of Biomolecules
Vitamins
2. Metabolic role:
– Homeostasis and normal metabolism
– Note: for the Leaving Certificate you need to
know one fat-soluble and one water-soluble
vitamin, their functions, and the diseases
caused by their deficiency
1.3.7 Metabolic Role of Biomolecules
• Vitamin A:
– Properties:
• Fat-soluble; 2 types: retinol (from animal sources) and
carotene (from plant sources); stored in liver
– Functions:
• Necessary for healthy epithelia tissue: skin, retina
(vision); bone growth; energy regulation; antioxidant
– Sources:
• Animal products: liver, eggs, milk
• Fruit and vegetables: carrots, tomatoes, sweet
potatoes, apricots
– Symptoms of vitamin A deficiency:
• Night-blindness
• Brain and spinal cord injury in infants
1.3.7 Metabolic Role of Biomolecules
• Vitamin D:
– Properties:
• Fat-soluble; 2 types:
– D2 (ergocalciferol - produced by UV action on skin)
– D3 (cholecalciferol - from animal sources)
– Functions:
• Necessary for proper uptake of calcium, teeth and
bone growth and bone mineralisation
– Sources:
• Main source is sunlight action on skin; cod liver oil
– Symptoms of vitamin D deficiency:
• Rickets in children
• Osteomalacia in adults (more frequent in women)
1.3.7 Metabolic Role of Biomolecules
• Vitamin E (tocopherol):
– Properties:
• Fat-soluble; stored in adipose tissue;
– Functions:
• Antioxidant - protects important biomolecules
such as protein and DNA from oxidation (damage)
– Sources:
• Vegetable oils, leafy green vegetables
• Whole grains, wheat germ, milk, eggs, meat, fish
– Symptoms of vitamin E deficiency:
• Muscle weakness and muscular dystrophy
• Sterility in animals
• Anaemia in infants
1.3.7 Metabolic Role of Biomolecules
• Vitamin K: fat-soluble in its natural form
– Properties: 3 types:
• K1: fat-soluble; food-based
• K2: fat-soluble; made by bacteria found in the gut
• K3: water-soluble; man-made; 2-3 times more
potent than K1 and K2
– Functions:
• Blood clotting
– Sources:
• K1: liver and green vegetables; K2: intestinal bacteria
– Symptoms of vitamin K deficiency:
• Bleeding - inability of wounds to form clots
1.3.7 Metabolic Role of Biomolecules
•
Vitamin B Complex Vitamins: 8 types
1.
2.
3.
4.
5.
6.
7.
8.
–
Thiamine (Vitamin B1)
Riboflavin (Vitamin B2)
Niacin/Nicotinic acid/Nicotinate (Vitamin B3)
Pyridoxine (Vitamin B6)
Folic acid/Folate
Cyanocobalamin (Vitamin B12)
Pantothenic acid/Pantothenate
Biotin
Functions:
•
All 8 vitamins of the B group function as coenzymes
(activate enzymes) involved in carbohydrate, protein
and DNA metabolism
1.3.7 Metabolic Role of Biomolecules
• Thiamine (Vitamin B1):
– Properties:
• Water-soluble
– Function:
• Coenzyme in carbohydrate metabolism
– Sources:
• Pork, wheat germ, yeast, black beans, sunflower seeds
– Symptoms of vitamin B1 deficiency:
• Beriberi (neurological and cardiovascular abnormalities)
1.3.7 Metabolic Role of Biomolecules
• Riboflavin (Vitamin B2):
– Properties:
• Water-soluble
– Function:
• Coenzyme in protein metabolism
– Sources:
• Organ meats, milk, vegetables
– Symptoms of vitamin B2 deficiency:
• Ariboflavinosis (lesions in mouth and lips)
1.3.7 Metabolic Role of Biomolecules
• Niacin/Nicotinic Acid/Nicotinate (Vitamin B3):
– Properties:
• Water-soluble
– Function:
• Coenzyme in carbohydrate metabolism
– Sources:
• Meat, peanuts, coffee
– Symptoms of vitamin B3 deficiency:
• Pellagra (dermatitis; diarrhoea, dementia)
1.3.7 Metabolic Role of Biomolecules
• Pyridoxine (Vitamin B6):
– Properties:
• Water-soluble
– Function:
• Coenzyme in protein metabolism
– Sources:
• Pork, liver, bananas, whole grains
– Symptoms of vitamin B6 deficiency:
• Extremely rare; no specific term for B6 deficiency;
symptoms include dermatitis and convulsions
1.3.7 Metabolic Role of Biomolecules
• Folic Acid/Folate:
– Properties:
• Water soluble
– Function:
• Necessary for DNA replication & formation of RBCs
– Sources:
• Liver, green leafy vegetables
– Symptoms of Folic Acid deficiency:
• Swollen tongue, heart-burn, diarrhoea, fatigue,
depression, megaloblastic anaemia, spina bifida
(which can be prevented by pregnant women taking folic
acid supplements); most common vitamin deficiency
1.3.7 Metabolic Role of Biomolecules
• Cyanocobalamin (Vitamin B12):
– Properties:
• Water-soluble; stored in the liver
– Function:
• Necessary for folic acid use in DNA replication
– Sources:
• Meat, fish, shellfish, poultry, milk
– Symptoms of vitamin B12 deficiency:
• Pernicious anaemia (sore tongue, numbness and
tingling in hands and feet, depression)
1.3.7 Metabolic Role of Biomolecules
• Pantothenic Acid/Pantothenate:
– Properties:
• Water-soluble
– Functions:
• Coenzyme in carbohydrate, lipid and protein
metabolism
– Sources:
• Liver, egg yolk, milk, brussels sprouts
– Symptoms of Pantothenic Acid deficiency:
• Extremely rare - has only occurred under
experimental conditions; has no specific term
1.3.7 Metabolic Role of Biomolecules
• Biotin:
– Properties:
• Water-soluble
– Functions:
• Coenzyme in lipid, protein, and DNA synthesis
– Sources:
• Intestinal bacteria can synthesise biotin, liver, meat
egg yolk, tomatoes
– Symptom of Biotin deficiency:
• Dermatitis
1.3.7 Metabolic Role of Biomolecules
• Ascorbic Acid/Ascorbate (Vitamin C):
– Properties:
• Water-soluble; most animals can manufacture their own
vitamin C - however, primates cannot
– Functions:
• Formation of collagen - maintenance of skin, gums,
cartilage, bones, blood vessels and wound healing;
antioxidant; facilitates iron absorption
– Sources:
• Citrus fruits, green peppers, tomatoes
– Symptoms of vitamin C deficiency:
• Scurvy (tender, sore gums that bleed very easily;
delayed wound healing)
Minerals
• Plants:
– Calcium (Ca):
• Required for the formation of the middle lamella
cement that glues neighbouring plant cells together
– Magnesium (Mg):
• Key component of chlorophyll - lack of magnesium
leads to a deficiency of chlorophyll and reduction in
photosynthesis
Minerals
• Animals:
– Calcium (Ca):
• Required for formation of teeth
• Growth and maintenance of bone
– Iron (Fe):
• Key component of haemoglobin - deficiency of iron
leads to lack of haemoglobin, resulting in anaemia
- tiredness and fatigue
1.3.8
Water
• Water is vital to life as we know it…
– It makes up 70 - 95% of cell mass
– It is an excellent solvent in which all biochemical
reactions occur
– It participates in chemical reactions - e.g.
photosynthesis, respiration and digestion
– Carries substances around the body of animals
and plants
– Carries substances into and out of cells
– Good absorber of heat energy
Anabolism and Catabolism
• Anabolism is the building up of large
biomolecules from smaller molecules
using energy
– e.g. photosynthesis and protein synthesis
• Catabolism is the breaking down of large
biomolecules into smaller molecules with
the release of energy
– e.g. respiration and digestion
Mandatory Experiment:
to conduct qualitative tests for:
a)
b)
c)
d)
Starch
Fat
A Reducing Sugar
A Protein
Title: (a) to test for starch
• Apparatus/Chemicals:
– Record the names of everything you use in the
experiment
• Method:
–
–
–
–
Label test tubes: A and B
Add 2 ml starch solution to test tube A
Add 2 ml of water to test tube B
Add a few drops of iodine solution to both test tubes
and mix
– Observe any colour changes and repeat experiment
• Results:
– Test tube A: red-yellow → blue-black
– Test tube B: no colour change
Title: (b) to test for fats
• Apparatus/Chemicals:
– Record the names of everything you use in the
experiment
• Method:
– Label two pieces of brown paper A and B
– Drop a few drops of water onto brown paper A
(control)
– Rub some butter onto brown paper B (test)
– Place both pieces of brown paper onto a radiator to
dry
– Repeat experiment
• Results:
– Brown paper A: not translucent
– Brown paper B: translucent
Title: (c) to test for a reducing sugar
• Apparatus/Chemicals:
– Record the names of everything you use in the experiment
• Method:
–
–
–
–
–
Label test tubes: A and B
Add 2 ml glucose solution to test tube A
Add 2 ml of water to test tube B
Add 2 ml of Benedict’s reagent to each test tube and mix
Observe any colour changes and repeat experiment
• Results:
– Test tube A: blue → brick red
– Test tube B: no colour change
Title: (d) to test for a protein
• Apparatus/Chemicals:
– Record the names of everything you use in the experiment
• Method:
–
–
–
–
–
Label test tubes: A and B
Add 2 ml diluted milk to test tube A
Add 2 ml of water to test tube B
Add 2 ml of sodium hydroxide to each test tube
Add a few drops of copper sulfate solution to both test
tubes and mix
– Observe any colour changes and repeat experiment
• Results:
– Test tube A: blue → violet
– Test tube B: no colour change