• Enzymes are catalysts that catalyse the biochemical reactions in the living system.
• Each enzyme has an active site into which the substrate molecule fits precisely. The ‘lock and key’ hypothesis postulated that the substrate fits precisely into the lock of the enzyme. This hypothesis has now been modified.
• The modern ‘induced fit’ hypothesis does not regard active site as a rigid structure but a flexible one, which modifies its shape to fit precisely the substrate molecule.
• Various factors like temperature, pH, substrate concentration and presence of inhibitors and activators influence the rate of enzyme catalysed reactions.
• Enzymes lower the activation energy of the reaction they catalyse.
• Simple single substrate enzyme catalysed reactions can be described by Michaelis-Menten kinetics which has a hyperbolic graph in terms of substrate concentration and initial velocity.
• Enzymes are also affected by the presence of inhibitors, like competitive, non-competitive and uncompetitive inhibitors, which slow down the rate of reaction or stop it completely.
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• Bioenergetics deals with the transformation and use of energy by living cell.
• There are two laws of thermodynamics. The first law states that energy can neither be created nor destroyed but can be converted into other forms of energy.
• The second law of thermodynamics states that entropy or disorder of universe is always increasing.
Combining the two laws of thermodynamics describe the free energy (G) change or the performance of work.
• The photosynthetic organisms derive free energy from the sunlight, whereas chemotrophs obtain free energy by oxidation of food stuff.
• This free energy is used to complete the cellular processes.
• This free energy is partly converted into ATP which is also known as universal currency of free energy.
• During energy releasing processes (breakdown), ATP is synthesised from ADP and inorganic phosphate (Pi), while in energy requiring processes ATP is broken into ADP and Pi.
