(1) Membrane Proteins:
Proteins and lipids form the major structural components of cell membrane. The membrane associated proteins consists of intrinsic proteins and extrinsic proteins. Many enzymes and enzyme systems are associated with membrane proteins i.e. components of electron transport system.
Enzymes are proteins produced within an organism which are capable of catalyzing specific catalytic reactions. They are biocatalysts which influence the rate f a chemical reaction, usually without undergoing any change themselves.
Several hormones are peptides and proteins. They play an important role in the regulation of metabolic reactions.
(4) Blood proteins:
The blood proteins include plasma proteins and haemoglobin.
(a) Plasma proteins are mainly albumin, globulins and fibrinogen. Albumin maintains the colloid osmotic pressure of plasma and transport materials. Globulins inhibit proteolytic enzymes, and helps to immunosystem of the body. Fibrinogen helps in blood clotting. Lipoproteins are concerned with transport of fat in blood.
(b) Haemoglobin is a conjugated protein consisting ofglobin and haeme. Haemoglobin carries oxygen in the form of oxyhaemoglobin in blood.
(5) Antibodies: Some antibodies like gramicidin S, tyrocidin and penicillin G are peptides.
(6) Nucleoproteins: These are conjugated proteins of cell nuclei.
(7) Multiple protein Assemblies: These contain several compounds which together from a functional unit.
(a) Collagen: A fibrous proteins found in many connective tissue.
(b) Flagella: Microtubules of flagella are made up of tubules.
(c) Actionmyosm complex of muscle: Muscle fibres consists of thin filaments of action, tropomyosin and troponin which make up the 1 or light bands and thick filaments of myosin which make up the A or dark bands.