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1. Explain the functions of protein in the body.

2. List the sources of protein.

3. State the elements of protein.

4. Differentiate between:

• Essential and non-essential amino acids and give examples

• High and low biological value proteins and give examples

Lesson ObjectivesProteins: Nutrients and Health

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Functions of Protein

• Enzymes help to speed up numerous chemical reactions in our body.

• E.g. Digestive enzymes are needed to break food into smaller substances during the process of digestion.

Formation of enzymes

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• Needed for the healthy growth of our body.

• To replace worn-out cells and tissues,or to repair the damaged ones.

Growth, repair and maintenance of body cells

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• Needed for making anitibodies, an essential component of our body’s immune system.

• Antibodies help to detect and fight harmful substances, thus protecting our body from illness and infection.

Maintain a healthy immune system

What do you think will happen to our body’s immune system if the

body is unable to make antibodies?

Functions of Protein

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Functions of Protein

• Used to provide energy for our body when the body’s supply of energy from carbohydrates and fats is low.

• Excess energy from proteins will be converted to fats and used as an energy reserve.

As an energy reserve

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Sources of Protein

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Elements of a protein molecule

•Carbon (C),

•Hydrogen (H),

•Oxygen (O),

•Nitrogen (N),

•and sometimes Sulphur (S) or Phosphorus (P)

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• An amino acid is made up of various chemical elements.

Peptide bond

• When two amino acids combine, they form a structure called peptide, bound by the peptide bond.

Elements of a protein molecule

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Elements of a protein molecule

• A polypeptide chain is formed when amino acids are linked together.

• A protein molecule is formed when a polypeptide chain grows longer and begins to fold into a complex structure.

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Types of amino acidsEssential and non-essential amino acids

• Cannot be produced by body

• Must be obtained from food

• Can be produced by the body

• Not necessary to obtain from food

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Examples of amino acidsEssential and non-essential amino acids

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Types of proteinsHigh or low biological value

Biological value refers to how well proteins in a food can be absorbed and used by our body.

What is biological value?

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Types of proteinsHigh biological value

Provide our body with all the essential A.A. in the right proportions.

Also known as complete proteins.

HBV proteins can be found inanimal sources (meat, poultry,seafood, milk and cheese) andsoya bean (plant source).

Proteins of HBV

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Types of proteinsLow biological value

Lack one or more essential A.A.

Also known as incomplete proteins.

LBV proteins can be found in plant sources (e.g. cereals such as rice and wheat; legumes, pulses and nuts), with the exception of soya beans.

Proteins of LBV

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Types of proteinsLow biological value

Proteins of LBV

Huh?What about strict

vegetarians (vegans)?

How do they ensure that they have all the essential amino

acids which their bodies need from plant sources alone?

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Types of proteinsLow biological value

Combining two or more plant foods which contain proteins of LBV can provide all of the essential A.A. which the body needs.

When two or more proteins of LBV are combined, they are known as complementary proteins.

Proteins of LBV

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Let’s Recap!

Four functions of proteins

Animal and plant sources of protein

Chemical elements of protein

Essential and non-essential amino acids

High and low biological value proteins 16