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Protein

Elemental Composition:

• Carbon (C)
• Hyrdrogen (H)
• Oxygen (O)
• Nitrogen (N)

 And sometimes:

• Sulpher (S)
• Phosphorous (P)
• Iron (fe)

Chemical Composition:
                                       
                           H                                                         H = hydrogen
                            |                                                          NH2 = Amino Group
                            |                                                          C = Carbon
         NH2------ C -------COOH                                  COOH = Carboxyl group 
                            |                                                          R = variable eg is H in Glycine
                            |
                           R


Essential amino acids are the amino acids that cannot be synthesised (made) by the bosy and must be obtained from food.
                    Eg. Threonine, Methionine, Lysine, Valine

Non-essential amino acids are the amino acids that can be synthesised by the body.
                    Eg. Serine, Alanine

Formation of a peptide link:

 

·        The H from the amino group of amino acid number 1 joins with the OH from the Carboxyl group of the second amino acid

·     This makes H₂O

·     Results in formation of peptide link and a water molecule

·     Condensation reaction

The reverse of this is Hydrolysis

Where water is added back into the protein to break the bonds

Eg digestion of food

Structures:

Three Types:      1. Primary structure

                             2. Secondary Structure

                             3. Tertiary structure

Primary Structure

·        The Number and order of amino acids on a polypeptide/protein chain.

Eg Insulin is mad up of 50 amino acids arranged in a definite            order

Secondary Structure

·        The further folding of the primary structure to give a definite shape

·        The folding is caused by links or bridges:

o   Di-sulphide link

o   Hydrogen bond

Di-sulphide link

·        Amino acid cysteine contains sulphur

·        Two Cysteine units on the same chain, or chains side by side, join and a di-sulphide link is formed

Hydrogen bond

·        Hydrogen from one amino acid joins with oxygen from another amino acid. Eg collagen 

Tertiary structure

·        The further folding of the secondary structure to give a 3-D shape.

·        Can be fibrous or globular

Fibrous – straight, curved or zigzag

E.g. elastin in meat

Globular – spherical in shape

E.g. ovalbumin in egg white

Classification of proteins:

1.   Simple Proteins -       From animals and plants

Contains only protein

2.   Conjugated Protein -          Contains a protein and a non-protein

3.   Derived Protein -        made by chemical or  enzymic action

From another protein

E.g. Caesinogen in milk to caesin

Sources of protein

Animal                                             Plant

Meat                                                 Pulse veg – peas, beans, lentils

Fish                                                  Nuts

Milk                                                 Cereals

Eggs                                                 Seeds

Cheese                                                          

                                                                                     Pulse veg – a veg that

                                                                                      grows in a pod