Proteins are made up of amino acids that are bonded together through peptide bonds. There are 20 amino acids that make up proteins, with 8 being essential amino acids that must be obtained through diet. Proteins have a primary, secondary, tertiary, and quaternary structure that determine their shape and function. Heat can cause proteins to denature and change shape through processes like coagulation and gelation. Proteins serve important structural and physiological roles in the body and a lack of protein can lead to growth issues and disease.

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

2. Elemental CompositionElemental Composition
Proteins are made up of atoms of:Proteins are made up of atoms of:
CarbonCarbon CC
HydrogenHydrogen HH
OxygenOxygen OO
NitrogenNitrogen NN
and sometimes Phosphorus (P), Sulphur (S) and Ironand sometimes Phosphorus (P), Sulphur (S) and Iron
(Fe)(Fe)
Nitrogen is needed for growth.Nitrogen is needed for growth.
Proteins are the only nutrients that contain theProteins are the only nutrients that contain the
element nitrogen.element nitrogen.
These elements are bonded together in smallThese elements are bonded together in small
molecules called amino acids.molecules called amino acids.
Amino acids are bonded together into long chainsAmino acids are bonded together into long chains
called proteinscalled proteins

3. Basic Structure of proteins –Basic Structure of proteins –
Amino AcidsAmino Acids
Proteins are made up ofProteins are made up of
chains of small moleculeschains of small molecules
called amino acids.called amino acids.
There are 20 different aminoThere are 20 different amino
acids but each has the sameacids but each has the same
basic structure.basic structure.
C = carbon atomC = carbon atom
H= Hydrogen atomH= Hydrogen atom
NNHH22 = Amino group (basic)= Amino group (basic)
COOH = Carboxyl groupCOOH = Carboxyl group
(acidic)(acidic)
R = Variable group, changesR = Variable group, changes
for every aminofor every amino
For example in the amino acidFor example in the amino acid
Glycine the R group = H (oneGlycine the R group = H (one
Hydrogen Atom)Hydrogen Atom)

5. Essential Amino AcidsEssential Amino Acids
There are over 20 different amino acids.There are over 20 different amino acids.
8 are8 are Essential Amino AcidsEssential Amino Acids that cannot be madethat cannot be made
by the body and must be eaten.by the body and must be eaten.
There are 2 extra essential amino acids forThere are 2 extra essential amino acids for
children.children.
The rest areThe rest are Non-Essential Amino AcidsNon-Essential Amino Acids thesethese
can be made by the bodycan be made by the body

6. Essential and Nonessential AminoEssential and Nonessential Amino
AcidsAcids

7. Essential Amino acids cannot be made by the body andEssential Amino acids cannot be made by the body and
must be obtained from foodmust be obtained from food
VVincent’sincent’s
LLovelyovely
MMotherother
TTookook
HHimim
TToo
LLondonondon
IInn
aa
PPramram
Valine
Lysine
Methionine
Trytophan
Histidine (children)
Threonine
Leucine
Isoleucine
Arginine (children)
Phenylalnine
8 essential for adults and 10 for children

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

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

10. Amino Acids Bonding to formAmino Acids Bonding to form
proteinprotein

11. Protein structure - PrimaryProtein structure - Primary
Order andOrder and
number of aminonumber of amino
acids in a proteinacids in a protein
chain forchain for
example theexample the
protein insulinprotein insulin
has over 50has over 50
amino acids in itsamino acids in its
chain arranged inchain arranged in
a definite order.a definite order.

12. Protein structureProtein structure
- Secondary- Secondary
Involves the folding of theInvolves the folding of the
protein chain into a spiral orprotein chain into a spiral or
zig-zag shapezig-zag shape
This structure is caused byThis structure is caused by
crosslinks that formcrosslinks that form
between different chains orbetween different chains or
within the one chain.within the one chain.
There are different typesThere are different types
of cross-linksof cross-links
(a)(a) Disulfide linksDisulfide links whichwhich
happen when 2 Sulphurhappen when 2 Sulphur
atoms bond .atoms bond .
(b)(b) Hydrogen bondsHydrogen bonds where awhere a
Hydrogen atom in one chainHydrogen atom in one chain
bonds with an Oxygen atombonds with an Oxygen atom
in another chain.in another chain.

13. Protein structure - TertiaryProtein structure - Tertiary
This refers to the 3 dimensionalThis refers to the 3 dimensional
folding of the chain. This structurefolding of the chain. This structure
can be globular or fibrous. Thecan be globular or fibrous. The
shapes give certain properties to theshapes give certain properties to the
proteinprotein
GlobularGlobular : In these the protein chain: In these the protein chain
is rolled up like a ball of wool. Thisis rolled up like a ball of wool. This
structure makes the protein soluble.structure makes the protein soluble.
This type of protein is found in bodyThis type of protein is found in body
cells, myoglobin in meat, albumin incells, myoglobin in meat, albumin in
egg, haemoglobin in blood.egg, haemoglobin in blood.
FibrousFibrous: In these the protein chain: In these the protein chain
takes on a straight, coiled or zig-zagtakes on a straight, coiled or zig-zag
shape. These shapes make theshape. These shapes make the
protein insoluble and stretchy orprotein insoluble and stretchy or
tough. Gluten in wheat and elastin intough. Gluten in wheat and elastin in
meat have a coiled structure.meat have a coiled structure.
Collagen in meat has a zig-zagCollagen in meat has a zig-zag
structure.structure.

14. Sources of proteinSources of protein
Animal proteinAnimal protein Plant proteinPlant protein
CheeseCheese Soya beansSoya beans
ChickenChicken TVPTVP
MeatMeat NutsNuts
FishFish LentilsLentils
EggsEggs PeasPeas
MilkMilk BeansBeans
CerealCereal

15. PROTEIN CLASSIFICATIONPROTEIN CLASSIFICATION
SIMPLESIMPLE CONJUGATEDCONJUGATED DERIVEDDERIVED
These proteins are formed dueThese proteins are formed due
to a chemical or enzyme action on ato a chemical or enzyme action on a
protein : i.e: Rennin acts onprotein : i.e: Rennin acts on
caesinogen and makes caesincaesinogen and makes caesin
PROTEIN + NON-PROTEINPROTEIN + NON-PROTEIN
Protein + Lipid =Protein + Lipid = LipoproteinLipoprotein (lecithin)(lecithin)
Protein + Phosphate =Protein + Phosphate = PhosphoproteinPhosphoprotein (caesin)(caesin)
Protein + nucleic acid =Protein + nucleic acid = NucleoproteinNucleoprotein (DNA)(DNA)
Protein + Colour Pigment =Protein + Colour Pigment = ChromoproteinChromoprotein (Haemoglobin)(Haemoglobin)
ANIMALANIMAL PLANTPLANT
ClassifiedClassified ClassifiedClassified GLUTENINSGLUTENINS : Soluble in acids & alkali: Soluble in acids & alkali
accordingaccording accordingaccording Glutenin in wheatGlutenin in wheat
to shapeto shape to solubilityto solubility
PROLAMINESPROLAMINES: Soluble in alcohol: Soluble in alcohol
FIBROUSFIBROUS GLOBULAR gliadin in wheatGLOBULAR gliadin in wheat
CollagenCollagen albuminalbumin

16. Properties of protein – effects ofProperties of protein – effects of
heat on proteinheat on protein
Effect of heatEffect of heat ExamplesExamples
Coagulation: protein setsCoagulation: protein sets
and then hardensand then hardens
Hard boiling eggsHard boiling eggs
Colour changeColour change Myoglobin in meat - red toMyoglobin in meat - red to
brownbrown
Maillards reaction (dryMaillards reaction (dry
heat)heat)
Bread crustBread crust
Tenderising (moist heat)Tenderising (moist heat) Collagen in meat changes toCollagen in meat changes to
gelatine and fibres fallgelatine and fibres fall
apartapart
Becomes indigestibleBecomes indigestible Overcooked meat orOvercooked meat or
cheese becomes tough andcheese becomes tough and
hard to digesthard to digest

17. 1.1. DenaturationDenaturation
Denaturation is a change in theDenaturation is a change in the
nature of the proteinnature of the protein
The protein chain unfolds, causing aThe protein chain unfolds, causing a
change to the structurechange to the structure
Denaturation is caused by a) heat,Denaturation is caused by a) heat,
b) chemicals andb) chemicals and
c) agitationc) agitation
It is often an irreversible processIt is often an irreversible process
A.A. HeatHeat
Most proteins coagulate/set whenMost proteins coagulate/set when
heated.heated.
E.g. Egg white coagulates at 60˚C;E.g. Egg white coagulates at 60˚C;
egg yolk coagulates in the stomachegg yolk coagulates in the stomach
at 68˚Cat 68˚C
B.B. ChemicalsChemicals
Acids, alkali, alcohol & enzymes causeAcids, alkali, alcohol & enzymes cause
changes to the protein structurechanges to the protein structure
E.g. Lemon juice added to milk causesE.g. Lemon juice added to milk causes
the milk protein caesinogen to curdlethe milk protein caesinogen to curdle
E.g. Enzyme rennin coagulates milkE.g. Enzyme rennin coagulates milk
protein caesinogen in the stomachprotein caesinogen in the stomach
C.C. AgitationAgitation
This is also known as mechanical actionThis is also known as mechanical action
It involves whipping or whisking theIt involves whipping or whisking the
proteinprotein
This results in the protein chainThis results in the protein chain
unfolding & partial coagulationunfolding & partial coagulation
Properties of ProteinProperties of Protein

18. 4.4. ElasticityElasticity
Certain proteins have an elasticCertain proteins have an elastic
property, e.g. Gluten, the proteinproperty, e.g. Gluten, the protein
found in flour, enables bread tofound in flour, enables bread to
rise during cookingrise during cooking
5.5. Foam FormationFoam Formation
When egg white is whisked, airWhen egg white is whisked, air
bubbles are formed as the proteinbubbles are formed as the protein
chains unravelchains unravel
Whisking also produces heat, whichWhisking also produces heat, which
slightly sets the egg whiteslightly sets the egg white
This foam will collapse after aThis foam will collapse after a
while, unless it is subjected to heatwhile, unless it is subjected to heat
This property is used to makeThis property is used to make
meringuesmeringues
Properties of Proteinof Protein

19. Properties of ProteinProperties of Protein
6.6. Gel formationGel formation
Collagen, when heated, formsCollagen, when heated, forms
gelatinegelatine
Gelatine can absorb largeGelatine can absorb large
amounts of water and, whenamounts of water and, when
heated, forms a solheated, forms a sol
On cooling, this becomes solidOn cooling, this becomes solid
& a gel is formed& a gel is formed
A gel is a semi-solid viscousA gel is a semi-solid viscous
solutionsolution
All gels have a three-All gels have a three-
dimensional network wherebydimensional network whereby
water becomes trapped. Thiswater becomes trapped. This
property is used in makingproperty is used in making
cheesecakes and souffléscheesecakes and soufflés
GelatineGelatine
Heat is appliedHeat is applied
As the proteinAs the protein
Uncoils waterUncoils water
becomes trappedbecomes trapped
SolSol
Pro gelPro gel
WaterWater
Protein Matrix – the mixture has set – itProtein Matrix – the mixture has set – it
has become a gelhas become a gel

20. Biological Functions of ProteinBiological Functions of Protein
Function typeFunction type FunctionFunction Result of deficiencyResult of deficiency
StructuralStructural
FunctionFunction
Growth & repairGrowth & repair
of body cellsof body cells
muscles &skinmuscles &skin
Retarded growthRetarded growth
Delayed healingDelayed healing
PhysiologicallyPhysiologically
active proteinactive protein
Making hormones,Making hormones,
enzymes,enzymes,
antibodies, bloodantibodies, blood
protein,protein,
nucleoproteinnucleoprotein
Body organs &Body organs &
systemssystems
malfunction.malfunction.
Easily infected.Easily infected.
Nutritive ProteinNutritive Protein Provides essentialProvides essential
amino acids foramino acids for
the body.the body.
Excess proteinExcess protein
used for energyused for energy
Lack of energy.Lack of energy.
Kwashiorkor,Kwashiorkor,
MarasmusMarasmus

21. DeaminationDeamination
This is the process byThis is the process by
which excess protein iswhich excess protein is
used for energy.used for energy.
Left over amino acidsLeft over amino acids
are brought to theare brought to the liverliver
TheThe NHNH22 groupgroup is brokenis broken
off, changed tooff, changed to
ammonia, then to ureaammonia, then to urea
and then excreted.and then excreted.
The rest of theThe rest of the
molecule is converted tomolecule is converted to
glucose and used forglucose and used for
releasing energy.releasing energy.

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

23. Biological Value of different proteinsBiological Value of different proteins
SourceSource FoodFood HBVHBV LBVLBV ProteinProtein
AnimalAnimal EggsEggs 100%100% Ovalbumin, Livetin, VitelinOvalbumin, Livetin, Vitelin
MilkMilk 95%95% Casein, Lactalbumin,Casein, Lactalbumin,
LactoglobulinLactoglobulin
MeatMeat 80-80-
90%90%
Collegen, Elastin, Myosin,Collegen, Elastin, Myosin,
FishFish Actin, Myosin, CollegenActin, Myosin, Collegen
GelatineGelatine 0%0% GelatineGelatine
PlantPlant SoyaSoya
BeansBeans
74%74%
RiceRice 67%67% OryzeninOryzenin
WheatWheat 53%53% GlutenGluten
MaizeMaize 40%40% ZeinZein

24. Supplementary Value of ProteinSupplementary Value of Protein
When low biological value foods, that lackWhen low biological value foods, that lack
essential amino acids, are eaten togetheressential amino acids, are eaten together
they can provide all the essential aminothey can provide all the essential amino
acid.acid.
The essential amino acids missing in oneThe essential amino acids missing in one
food can be made up for by being presentfood can be made up for by being present
in the other food and visa versa.in the other food and visa versa.
This complementary value of proteinThis complementary value of protein
means that vegans can get all themeans that vegans can get all the
essential amino acids without eatingessential amino acids without eating
animal foodanimal food
Example; Bread is lacking Lysine but isExample; Bread is lacking Lysine but is
high in Methionine. Beans are lackinghigh in Methionine. Beans are lacking
Methionine but high in Lysine. By eatingMethionine but high in Lysine. By eating
beans on toast both essential amino acidsbeans on toast both essential amino acids
are included in the meal.are included in the meal.

25. RDA Protein & Energy valueRDA Protein & Energy value
RDARDA
1gram of protein per kilogram of body weight.1gram of protein per kilogram of body weight.
Child 30-50g/dayChild 30-50g/day
Teenager 60-80g/dayTeenager 60-80g/day
Adults 50-75g/dayAdults 50-75g/day
Pregnant or lactating 70-85g/dayPregnant or lactating 70-85g/day
Energy ValueEnergy Value
1g of protein gives 4kCal or 17 kJ energy1g of protein gives 4kCal or 17 kJ energy

26. Digestion of proteinDigestion of protein
Part ofPart of
SystemSystem
PhysicalPhysical
DigestionDigestion
DigestiveDigestive
JuiceJuice
EnzymeEnzyme SubstrateSubstrate ProductProduct
MouthMouth ChewedChewed
StomachStomach ChurnedChurned GastricGastric
juicejuice
RenninRennin
PepsinPepsin
CaseinogenCaseinogen
ProteinsProteins
CaseinCasein
PeptonesPeptones
DuodenumDuodenum PancreaticPancreatic
JuiceJuice
TrypsinTrypsin ProteinProtein PeptonesPeptones
SmallSmall
IntestineIntestine
IntestinalIntestinal
JuiceJuice
PeptidasePeptidase PeptonesPeptones Amino acidsAmino acids

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

28. Questions??Questions??
1 What is the elemental composition of protein?1 What is the elemental composition of protein?
2 Draw the chemical structure of an amino acid2 Draw the chemical structure of an amino acid
3 Explain how a peptide link forms3 Explain how a peptide link forms
4 What are essential amino acids?4 What are essential amino acids?
5 List the biological functions of protein.5 List the biological functions of protein.
6 What is meant by ‘biological value’ of protein?6 What is meant by ‘biological value’ of protein?
7 Difference between denaturation & deamination7 Difference between denaturation & deamination
8 List (a) the energy value (b) the RDA of protein?8 List (a) the energy value (b) the RDA of protein?
9 List 4 sources of (a) HBV and (b) LBV protein.9 List 4 sources of (a) HBV and (b) LBV protein.
10 Describe the digestion of protein in humans.10 Describe the digestion of protein in humans.