1. To know the functions, sources & biological value of protein (4.2a,c)
Year 13 Proteins (p13-15)
Aims
To know the functions, sources & biological value of protein (4.2a,c)
To understand the role of protein as part of a well balanced diet (4.2a)
To be able to make a high quality Sponge Fruit Flan (4.4 b eggs, 4.4 c whisking)

2. Concept of nutrition Balanced diet DRV EAR RNI GDA Malnutrition
Key terms
Concept of nutrition
Balanced diet
DRV
EAR
RNI
GDA
Malnutrition

3. Key terms Concept of nutrition –
nutrition is the study of the nutrients in food, how the body uses nutrients & the relationship between diet, health & disease’. (now also includes wider social issues and impact on food consumption)
Balanced diet –
A diet that contains all the nutrients in the correct proportions to meet a person’s needs.
Affected by: Age, Gender, Body build, State of health
DRV –
Dietary reference values
EAR –
Estimated average requirement
RNI –
Reference nutrient intake
RI –
Reference intake (replaced GDA)
Malnutrition –
a deficiency, excess or imbalance of nutrients that causes adverse effects on health & wellbeing

4. Proteins Essential in human diet Only nutrient supplying NITROGEN
Nitrogen vital for cell formation & growth
Built from AMINO ACIDS
Molecules containing an amine group (NH2) & an acid group (COOH)
CARBON HYDROGEN OXYGEN + NITROGEN
Some contain sulphur & phosphorous (CHONPS)
20 different amino acids
Joined in various combinations (like building blocks)

5. Structure of Amino Acids
All same structure H
R C COOH (carboxyl group
weakly acidic)
NH2
(amino group
Varies between
one amino acid
& another

6. Amino Acids Have ability to link together Form PROTEIN CHAINS
One AMINO ACID reacts with
ACIDIC CARBOXYL GROUP of next
Water is eliminated
Link that occurs between AAs =
PEPTIDE LINK (CONH)
Long chains that form =
POLYPEPTIDE CHAINS

7. R R O H 0 NH2 C C N C C H OH H H OH H2O CONDENSATION = WATER REMOVED
Polypeptide Chains R
R O H
NH C C N C C
H OH H H OH
H2O
CONDENSATION = WATER REMOVED
H2O
Added =
Hydrolysis

8. Reverse Action Called Hydrolysis One molecule of water added
Causes protein to break into AMINO ACIDS
Happens during digestion

9. Protein Molecules Consist of several adjacent polypeptide chains
Can be FOLDED,COILED OR CROSS LINKED at intervals
Simple protein = insulin (pancreatic hormone) =
50 amino acids
Complicated protein = haemoglobin =
500 amino acids

10. 1. Globular Proteins – proteins consisting of coiled chain
Structure of Proteins
3 types
1. Globular Proteins – proteins consisting of coiled chain
- water soluble
- easily denatured
- e.g. ALBUMEN & GLOBULIN
- occur in milk & egg white

11. Structure of Proteins
2. Fibrous Proteins – polypeptide chains twisted into
springs
- like coils & zig zags
- elastic property
- e.g. ELASTIN (protein in meat tendons)
GLUTEN (protein in flour)
- zig zag structure produces tough non
elastic protein
- eg COLLAGEN found in connective
tissue

12. Structure of Proteins protein - e.g. PIGMENT
3. Conjugated proteins – chemically combined with a non
protein
- e.g. PIGMENT
PIGMENT + PROTEIN = HAEMOGLOBIN
- classed according to non protein
group
e.g. PHOSPHOPROTEINS – contain
phosphate groups such as
CASEIN in milk
Cross links joining polypeptide chains can be H bonds, salt links & most importantly DISULPHIDE links – give great toughness & steady shape e.g. GLUTEN in flour

13. Denaturisation When protein molecules UNTWIST
Causes loss of structure & function
IRREVERSIBLE
Caused by
1. Heat – most frequent cause.
- especially albumen in eggs
- causes linking bonds to break
- protein loses H2O binding power
- considerable shrinkage
Protein coagulates - molecules packed more tightly which causes
–skin to form on milk
Custard to curdle or egg white to harden
If heat applied slowly & not raised above 60ºF curdling should not occur

14. Denaturisation 2. Mechanical action – e.g. whipping, shaking
- when egg white is whisked breaks cross links & denatures.
3. Some Chemicals
ACIDS – lemon juice added to milk – lactic acid formed
When milk is sour may bring about coagulation of milk protein
ALCOHOL & VINEGAR – preservative effect on food – denature enzymes which cause destruction of food.

15. Essential Amino Acids Body can manufacture some Amino Acids
8 which it can’t = ESSENTIAL AMINO ACIDS
Further 2 are required by growing children
Protein needed for growth and repair
Also secondary energy source

16. Biological Value Proteins
Tells us how nourishing a protein is
2 types
HIGH BIOLOGICAL VALUE e.g. meat, eggs, cheese, fish.
Contain all essential amino acids in proportion required by human body
Most of nitrogen available for growth & repair
Eggs have highest B.V 100%, Milk 95%, Meat & fish 80 – 90%
LOW BIOLOGICAL VALUE – deficient in one or more essential amino acid
Usually from vegetable sources e.g. beans, bread, nuts, peas (fresh & processed), whole cereals
SUPPLEMENTARY VALUE (complimentary)
When mixed together e.g. beans on toast, hummus & pitta bread, Dahl & chapati – biological value increased
Individually beans & bread LBV but eaten together provide HBV
BIOLOGICAL VALUE = % ABSORBED PROTEIN that is converted to body protein

17. Homework Protein test – Friday 8th July
Monday 27th – Scotch eggs, mayonnaise & coleslaw