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1 of the 3 macronutrients
Elemental Composition
Proteins are made up of atoms of:
 Carbon
C
 Hydrogen
H
 Oxygen
O
 Nitrogen
N
 and sometimes small amounts of Phosphorus (P),
Sulphur (S) and Iron (Fe)
 Nitrogen is needed for growth.
 Proteins are the only nutrients that contain the
element nitrogen.
 These elements are bonded together in small
molecules called amino acids.
 Amino acids are bonded together into long chains
called proteins
Basic Structure of protein – Amino
Acids
 There are 20 different amino
acids but each has the same
basic structure.
C = carbon atom
H= Hydrogen atom
NH2 = Amino group
COOH = Carboxyl group
R = Variable group
e.g. in the amino acid Glycine the R
= H (one Hydrogen Atom)
H
COOH
C
R
NH2
Formation of a Peptide Bond
H
COOH
C
R
H
NH2
COOH
C
R
NH
2
Biological Value of Protein
The Biological Value of a protein is a measure of the quality of the
protein and is expressed as a %.
High Biological Value
• Contain all essential Amino
Acids in the correct
proportion for the bodies
needs
• Complete proteins
• Animal sources
Low Biological Value
• Lack some essential amino
acids or do not contain them
in the correct proportion
• Incomplete protein
• Plant sources
Sources of protein
Animal protein
Cheese 26%
Meat 20%
Fish 17%
Eggs 12%
Milk 3%
Plant protein
Soya beans 40%
Nuts 24%
Rice 7 %
Peas 6%
Beans
Chicken
Peas
Lentils
Cereals
Essential Amino Acids
 There are over 20 different amino acids.
 8 are Essential Amino Acids that cannot be made by
the body and must be eaten e.g. Lysine, Leucine,
Isoleucine.
 There are 2 extra essential amino acids for children-
Arginine and Histidine
 The rest are Non-Essential Amino Acids these can be
made by the body e.g. Glycine, Cystine, Cysteine.
Supplementary Value of Protein
 When low biological value foods, that lack essential
amino acids, are eaten together they can provide
all the essential amino acids.
 The essential amino acids missing in one food can
be made up for by being present in the other food
and visa versa.
 This complementary value of protein means that
vegans can get all the essential amino acids without
eating animal food
 Example; Bread is lacking Lysine but is high in
Methionine. Beans are lacking Methionine but high
in Lysine. By eating beans on toast both essential
amino acids are included in the meal.