- Proteins are complex compounds that made up of carbon, hydrogen and nitrogen. Some proteins contain sulphur and phosphorus.
- It is needed by the body for
- growth,
- repair of damaged tissues and
- synthesis of secretions (enzymes, mucus, hormones.)
- Proteins are polymer that made up of monomers called amino acids. Each molecule of amino acid has one amino group (-NH2) and one carboxyl group ( -COOH).
- Two molecules of amino acids are joined by a peptide bond to form a dipeptide through condensation. Amino acid + amino acid → dipeptide + water
- Polypeptides (protein) are formed when many amino acids are joined together by condensation.
- Proteins can be broken down through hydrolysis into amino acids.
- There are 20 types of amino acids in cells.
- Amino acid can be divided into essential amino acid and nonessential amino acid.
- Essential amino acids are amino acids that cannot be synthesised by the body. They can only be obtained from diets. An example is leucine.
- Non-essential amino acids are amino acids that can be synthesised by the body. They are derived from other amino acids. There are 11 non-essential amino acids.
- Proteins can be grouped into four levels of organisation according to their structures.
- Primary structure (linear sequence of amino acids in a polypeptide.)
- Secondary structure (polypeptide is coiled to form an alpha-helix or folded into beta-pleated sheets)
- Tertiary structure (helix or beta-pleated sheets are folded in many ways into a three dimensional shape of a polypeptide.)
- Examples are hormones, enzymes, antibodies and plasma proteins.
- Quarternary structure (Two or more tertiary structure polypeptide chains combine to form a large and complex protein molecule. Example: haemoglobin.)