SS3 First Term Chemistry Lesson Note – Giant Molecules II

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WEEK 6

TOPIC: GIANT MOLECULES

CONTENTS:

1. Protein-sources
2. Test for protein and uses of protein.
3. Enzymes and they functions.

PERIOD 3:  PROTEINS

Proteins are one of the four major groups of macromolecules or polymers that are present in all living organisms carrying out various functions needed by cells. They may be regarded as the products needed by cells. They may be regarded as the products of successive condensations between the carboxyl group of one amino acid and the amino – group of another amino-acid. The structure of most enzymes indicates that they are proteins.

Sources

Proteins are found in all living systems as structural components and as biologically important substances such as hormones enzymes and pigments.  Proteins in our food contain essentially amino acids and these are called first class proteins. They are mainly of animal origin. Examples include lean meat, fish, eggs, milk, cheese and chicken second class proteins are of plant origin and are found in vegetables, legumes (e.g beans, soya beans), groundnuts, grapes, apple etc. Example of proteins includes:

1. Keratin – a compound of skin, heart and nails
2. Collagen – a muscle protein
3. Insulin – a peptide hormone regulating the blood sugar level.
4. Elastin – a duef constituent of elastic fibres
5. Amylase – present in human saliva and capable of breaking starch down into sugar
6. Haemoglobin – a pigment that carries oxygen in the blood, and Ribonuclease.

Structure and shape of proteins

Proteins have well defined structures. The primary structures of a protein refer to the way in which the atoms of the protein molecules are joined to one another by covalent bonds to form chains and cross-linkages between chains. Amino – acids are the basic structural units of proteins. Each amino acid contains an amino group (-NH₂) and carboxyl (-COOH) in its molecule. A particular protein molecule may contain two or more different amino-acids, linked in a sequence that reoccurs regularly along the protein chain. No two proteins have the same sequence, even if they contain the same types of amino-acids.

Formation of peptides

The amino-acids that make up [a macromolecule of protein are linked in such a way that a molecule of water is eliminated between the carboxyl group of one amino acid and the amino group of another, to form an amide called peptide. Thus, combination of two or more   amino acids forms peptides, combination of three amino acids form tripeptides, combination of many amino-acids form polypeptides. It is a chain reaction.

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