WEEK 7: DIGESTIVE ENZYMES
An enzyme can be defined as an organic
catalyst which speed up the rate of
chemical changes in living cells but are
not used up in the process. There are two
major types of enzymes:
(1) Intracellular enzymes: These are
enzymes that function inside the cells
of living organisms e.g. respiratory
enzymes in the mitochondrion
(2) Extracellular enzymes: These are
enzymes that functions outside the
cells e.g. digestive enzymes.
CHARACTERISTICS OF ENZYMES
(a) Enzymes are protein in nature
(b) Enzymes speed up the rate of
chemical reactions
(c) Enzymes act in very small quantity
(d) Enzymes are involved in reversible
reaction
(e) Enzymes are specific in action
(f) Enzymes can function outside the
organism producing them
(g) Enzymes are affected by the pH of
their surroundings.
(h) Enzymes have specific temperature
range.
LOCATIONS, SOURCES AND FUNCTIONS
OF ENZYMES
Enzym Source Locatio Effect/Function
es n
1 Ptyalin Salivar Mouth Convert starch to
y gland maltose
2 Renin Gastric Stomac Coagulates milk
gland h
3 Pepsin Gastric Stomac
Converts protein to
gland h peptones
4 Lipase Pancre Duoden
Converts fats and
as um oils to fatty acids
and glycerol
5 Amylas Pancre Duoden Convert starch to
e as um maltose
6 Trypsin Pancre Duoden Converts peptones
as um to polypeptides
7 Erepsin Succus Small Converts
entricu intestin polypeptides to
s e amino acids
8 Maltase Succus Small Converts maltose
entricu intestin to glucose
s e
9 Sucras Succus Small Convert sucrose to
e entricu intestin glucose
s e
WEEK 8: CLASSES OF FOOD
There are six major classes of food eaten
by man. These six classes of food include
carbohydrate, proteins, fats and oils
(lipids), minerals, vitamins and water.
(1) Carbohydrates: This is made up of
carbon, hydrogen and oxygen with a
general formula of Cx (H2O)y. It can be
obtained from sources such as rice,
maize, bread, yam, etc. There are three
major types of carbohydrates.
Types Other Sug Formula Exampl
name ar es
unit
A Monosacchar Simple One C6H12O6 Glucose
ide sugar ,
fructos
e,
galacto
se
B Disaccharide Reduci Two C12H22O11 Sucrose
ng ,
sugar maltose
,
lactose.
C Polysacchari Comple Mor (C6H10O5 Cellulos
de x sugar e )n e,
than starch.
two
Importance of carbohydrates includes:
(a) It provides energy required by
animals
(b) It provides heat for maintaining body
temperature
(c) It is used for building certain parts of
the body
(d) It is used as lubricant (mucus).
(2) Proteins: Proteins are complex
molecules made up of smaller units called
amino acids. Proteins consist of carbon,
hydrogen, oxygen, nitrogen and
sometimes phosphorus and sulphur.
Protein digestion involves the following
process:
Proteins – Peptones – Polypeptides –
Amino acids. Sources of protein include
fish, egg, meat, etc. Importance of protein
includes:
(a) It is used for growth of young ones.
(b) It is used for the repair of worn-out
tissues.
(c) It aids reproduction
(d) It is used for the production of
enzymes and hormones
(3) Fats and Oils (Lipids): At room
temperature, fats are solid while oils are
liquid. Fats and oils are digested into fatty
acids and glycerol. Sources of fats and
oils include palm oil, cheese, margarine,
butter, melon oil, etc. Importance of fats
and oils include
(a) Fats and oils provide more energy
than carbohydrates.
(b) They supply essential fatty acids to
the body.
(c) They are used to maintain body
temperature.
(d) They provide fat soluble vitamins to
the body.
(4) Mineral salts: These minerals are
already present in other classes of food.
They include calcium, phosphorus,
potassium, chlorine, iron, magnesium,
iodine, etc. Mineral salts can be obtained
from sources such as milk, vegetable,
egg, beans, etc. Mineral salts make the
body strong and healthy.
(5) Vitamins: Vitamins are organic food
substances required in small quantity.
Examples of vitamin are vitamin A, B1, B2,
B12, C, D, E, K, etc. Vitamins can be
obtained from sources such as fresh
fruits, milk, vegetables, egg, etc. Vitamins
help to keep the body healthy and to
prevent some diseases.
(6) Water: Water is composed of
hydrogen and oxygen. Sources of water
include rain, tap, pond, stream, etc.,
Importance of water include
(a) It is required for food digestion
(b) It is required for metabolic activities in
the body
(c) It is the main component of the body
(about 75% of the body)
(d) It aids the excretion of metabolic
waste
(e) It acts as a transport medium for
nutrients
Balanced diet is a diet containing the
correct proportion of
BALANCED DIET all the six classes of food
required by the body. The recommended
percentage composition of the six classes
of food in a balanced diet is as follows:
(a) Carbohydrates = 60%
(b) Proteins = 15%
(c) Fats and oils = 15%
(d) Vitamins, minerals and water = 10%
IMPORTANCE OF BALANCED DIET
(a) Balanced diet encourages normal
growth and development.
(b) Balanced diet provides energy for
normal activities.
(c) Balanced diet makes us healthy.
(d) Balanced diet prevents malnutrition
deficiency such as kwashiorkor and
beriberi.
FOOD TEST
Food Test Observatio Inferenc
n e
1 Starch Add few drops Colour Starch
of iodine to change to is
bread or yam. blue-black present
2 Water Dip a blue dry Paper Water
cobalt chloride colour is
paper into a changes present
food from blue
substance to pink
3 Simple (a) put glucose A brick-red Glucose
sugar e.g solution in a or orange is
glucose test tube precipitate present
(b) Add 2% is seen
Benedict
solution
(c) Boil the
mixture for 4-6
minutes
4 Reducing (a) Put sucrose A yellow Sucrose
sugar solution in test precipitate is
e.g. tube is seen present
sucrose (b) Add few
drops of
Benedict or
Fehling
solution
(c) Add few
drops of HCl
(d) Boil the
mixture for
few minutes
5 Fats and (a) Add a The oil spot Fats or
Oils drop of oil on allows light oils is
(Transluce
a filter paper to pass present
nt test) (b) Observe through it
the spot (it is
against translucent
candle light
6 Fats and (a) Add a few The red Fats or
Oils drops of colour will oils is
(Sudan Sudan (III) change to present
test) solution to oil black
in a test tube precipitate
(b) Boil the
solution
7 Protein (a) Add 1cm3 Mixture will Protein
(Biuret of protein to turn to is
test) NaOH in a purple or present
test tube violet
(b) Add 1% colour
copper (II)
solution in
drops
(c) Shake the
mixture after
each drop
8 Protein (a) Put 3cm3 A red Protein
(Millon’s of protein in precipitate is
test) a test tube would present
(b) Add 3cm3 appear
of Millon’s
reagent
(c) Warm the
mixture in a
bath
