1. The Building Blocks of our Body
Proteins
The Building Blocks of our Body
© PDST Home Economics

2. Elemental Composition
Proteins are made up of atoms of:
Carbon C
Hydrogen H
Oxygen O
Nitrogen N
and sometimes 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

3. Basic Structure of proteins – Amino Acids
Proteins are made up of chains of small molecules called amino acids.
There are 20 different amino acids but each has the same basic structure.
C = carbon atom
H= Hydrogen atom
NH2 = Amino group (basic)
COOH = Carboxyl group (acidic)
R = Variable group, changes for every amino
For example in the amino acid Glycine the R group = H (one Hydrogen Atom)

5. 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.
There are 2 extra essential amino acids for children.
The rest are Non-Essential Amino Acids these can be made by the body

6. Essential and Nonessential Amino Acids

7. 8 essential for adults and 10 for children
Essential Amino acids cannot be made by the body and must be obtained from food
Vincent’s
Lovely
Mother
Took
Him To
London In a
Pram
Valine
Lysine
Methionine
Trytophan
Histidine (children)
Threonine
Leucine
Isoleucine
Arginine (children)
Phenylalnine
8 essential for adults and 10 for children

8. Peptide Bonds or Links
Amino acids join together into long chains called proteins.
Just like the 26 letters of the alphabet can form thousands of words by linking in different ways; the 20 amino acids can form many different proteins
The bond that links one amino acid to another is called a peptide link or bond
Each time 2 amino acids link together a water molecule is taken away and so the linking process is called Condensation.
The reverse of condensation is called Hydrolysis, water molecules are added to protein chains and split the amino acids apart, this happens during protein digestion.

9. Peptide Bonds or Links
The Amino group (NH2) of one amino acid links with the Carboxyl group (COOH) of another amino acid.
The Amino group (NH2) looses one H, the Carboxyl group (COOH) looses an OH group.
The H and OH bond together to form a water molecule (H2O)
The remaining CO and NH bond together to form a peptide link.
Two amino acids joined is called a Dipeptide
Many amino acids joined in a chain is called a Polypeptide

10. Amino Acids Bonding to form protein

11. Protein structure - Primary
Order and number of amino acids in a protein chain for example the protein insulin has over 50 amino acids in its chain arranged in a definite order.

12. Protein structure - Secondary
Involves the folding of the protein chain into a spiral or zig-zag shape
This structure is caused by crosslinks that form between different chains or within the one chain.
There are different types of cross-links
(a) Disulfide links which happen when 2 Sulphur atoms bond .
(b) Hydrogen bonds where a Hydrogen atom in one chain bonds with an Oxygen atom in another chain.
Nother

13. Protein structure - Tertiary
This refers to the 3 dimensional folding of the chain. This structure can be globular or fibrous. The shapes give certain properties to the protein
Globular : In these the protein chain is rolled up like a ball of wool. This structure makes the protein soluble. This type of protein is found in body cells, myoglobin in meat, albumin in egg, haemoglobin in blood.
Fibrous: In these the protein chain takes on a straight, coiled or zig-zag shape. These shapes make the protein insoluble and stretchy or tough. Gluten in wheat and elastin in meat have a coiled structure. Collagen in meat has a zig-zag structure.

14. Sources of protein Animal protein Plant protein Cheese Soya beans
Chicken
TVP
Meat
Nuts
Fish
Lentils
Eggs
Peas
Milk
Beans
Cereal

15. PROTEIN CLASSIFICATION
SIMPLE CONJUGATED DERIVED
These proteins are formed due
to a chemical or enzyme action on a
protein : i.e: Rennin acts on
caesinogen and makes caesin
PROTEIN + NON-PROTEIN
Protein + Lipid = Lipoprotein (lecithin)
Protein + Phosphate = Phosphoprotein (caesin)
Protein + nucleic acid = Nucleoprotein (DNA)
Protein + Colour Pigment = Chromoprotein (Haemoglobin)
ANIMAL PLANT
Classified Classified GLUTENINS : Soluble in acids & alkali
according according Glutenin in wheat
to shape to solubility
PROLAMINES: Soluble in alcohol
FIBROUS GLOBULAR gliadin in wheat
Collagen albumin

16. Properties of protein – effects of heat on protein
Effect of heat
Examples
Coagulation: protein sets and then hardens
Hard boiling eggs
Colour change
Myoglobin in meat - red to brown
Maillards reaction (dry heat)
Bread crust
Tenderising (moist heat)
Collagen in meat changes to gelatine and fibres fall apart
Becomes indigestible
Overcooked meat or cheese becomes tough and hard to digest

17. Properties of Protein Denaturation Chemicals
Denaturation is a change in the nature of the protein
The protein chain unfolds, causing a change to the structure
Denaturation is caused by a) heat, b) chemicals and
c) agitation
It is often an irreversible process
Heat
Most proteins coagulate/set when heated.
E.g. Egg white coagulates at 60˚C; egg yolk coagulates in the stomach at 68˚C
Chemicals
Acids, alkali, alcohol & enzymes cause changes to the protein structure
E.g. Lemon juice added to milk causes the milk protein caesinogen to curdle
E.g. Enzyme rennin coagulates milk protein caesinogen in the stomach
Agitation
This is also known as mechanical action
It involves whipping or whisking the protein
This results in the protein chain unfolding & partial coagulation

18. Properties of Protein Solubility
Proteins are generally insoluble in water
There are two exceptions – egg white in cold water & connective tissue, which is converted to gelatine in hot water
Maillard reaction
Maillard reaction is also known as non-enzymic browning. It occurs when food is roasted, baked or grilled
Amino Acid + Carbohydrates + Dry heat = Brown Colour
Examples include roast potatoes, toast
Elasticity
Certain proteins have an elastic property, e.g. Gluten, the protein found in flour, enables bread to rise during cooking
Foam Formation
When egg white is whisked, air bubbles are formed as the protein chains unravel
Whisking also produces heat, which slightly sets the egg white
This foam will collapse after a while, unless it is subjected to heat
This property is used to make meringues

19. Properties of Protein Gelatine Heat is applied Gel formation
Collagen, when heated, forms gelatine
Gelatine can absorb large amounts of water and, when heated, forms a sol
On cooling, this becomes solid & a gel is formed
A gel is a semi-solid viscous solution
All gels have a three-dimensional network whereby water becomes trapped. This property is used in making cheesecakes and soufflés
Gelatine
Heat is applied
As the protein
Uncoils water
becomes trapped
Sol
Pro gel
Water
Protein Matrix – the mixture has set – it has become a gel

20. Biological Functions of Protein
Function type
Function
Result of deficiency
Structural Function
Growth & repair of body cells muscles &skin
Retarded growth
Delayed healing
Physiologically active protein
Making hormones, enzymes, antibodies, blood protein, nucleoprotein
Body organs & systems malfunction. Easily infected.
Nutritive Protein
Provides essential amino acids for the body.
Excess protein used for energy
Lack of energy.
Kwashiorkor, Marasmus

21. Deamination
This is the process by which excess protein is used for energy.
Left over amino acids are brought to the liver
The NH2 group is broken off, changed to ammonia, then to urea and then excreted.
The rest of the molecule is converted to glucose and used for releasing energy.

22. Biological Value of Protein
The Biological Value of a protein is a measure of the quality of the protein and is expressed as a %.
It is decided by the number of essential amino acids a protein contains in proportion to how much of them the body needs.
There are 2 types of protein foods:
(a) High Biological value, contain all essential Amino Acids, complete proteins, animal sources.
(b) Low Biological value, lack some essential amino acids, incomplete protein, plant sources

23. Biological Value of different proteins
Source
Food
HBV
LBV
Protein
Animal
Eggs
100%
Ovalbumin, Livetin, Vitelin
Milk
95%
Casein, Lactalbumin, Lactoglobulin
Meat
80-90%
Collegen, Elastin, Myosin,
Fish
Actin, Myosin, Collegen
Gelatine 0%
Plant
Soya Beans
74%
Rice
67%
Oryzenin
Wheat
53%
Gluten
Maize
40%
Zein

24. Supplementary Value of Protein
When low biological value foods, that lack essential amino acids, are eaten together they can provide all the essential amino acid.
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.

25. RDA Protein & Energy value
1gram of protein per kilogram of body weight.
Child 30-50g/day
Teenager 60-80g/day
Adults 50-75g/day
Pregnant or lactating 70-85g/day
Energy Value
1g of protein gives 4kCal or 17 kJ energy

26. Digestion of protein Part of System Physical Digestion Digestive Juice
Enzyme
Substrate
Product
Mouth
Chewed
Stomach
Churned
Gastric
juice
Rennin
Pepsin
Caseinogen
Proteins
Casein
Peptones
Duodenum
Pancreatic
Juice
Trypsin
Protein
Small Intestine
Intestinal Juice
Peptidase
Amino acids

27. Absorption & Assimilation of Amino Acids
Amino Acids are absorbed into blood capillaries in the villi of the small intestine.
These capillaries connect into the portal vein which carries the amino acids to the Liver.
From here the Amino Acids will be sent to (a) replace & repair body cells, (b) form new cells, antibodies, hormones, enzymes or (c) be deaminated

28. Questions?? 1 What is the elemental composition of protein?
2 Draw the chemical structure of an amino acid
3 Explain how a peptide link forms
4 What are essential amino acids?
5 List the biological functions of protein.
6 What is meant by ‘biological value’ of protein?
7 Difference between denaturation & deamination
8 List (a) the energy value (b) the RDA of protein?
9 List 4 sources of (a) HBV and (b) LBV protein.
10 Describe the digestion of protein in humans.