Once an enzyme makes a transcript longer than 10 nucleotides, it is said to have escaped the promoter. At this point, it has formed a stable ternary complex, containing enzyme, DNA, and RNA. This is the transition to the elongation phase.

TLS Online TPP Program

#Id: 8545

#Unit 1. Molecules and their Interaction Relevant to Biology

Irreversible inhibitors, such as the organophosphorus and organomercury compounds, cyanide, carbon monoxide and hydrogen sulphide, combine with the enzyme to form a covalent bond. 

TLS Online TPP Program

#Id: 8546

#Unit 1. Molecules and their Interaction Relevant to Biology

The extent of irreversible inhibition of the enzyme is dependent upon the reaction rate constant (and hence time) for covalent bond formation and upon the amount of inhibitor present.

TLS Online TPP Program

#Id: 8547

#Unit 1. Molecules and their Interaction Relevant to Biology

The irreversible inhibitors cannot be removed by simple physical techniques such as dialysis, is to reduce the amount of enzyme available for reaction.

TLS Online TPP Program

#Id: 8548

#Unit 1. Molecules and their Interaction Relevant to Biology

TLS Online TPP Program

#Id: 8549

#Unit 1. Molecules and their Interaction Relevant to Biology

The irreversible inhibition involves reactions with a functional group, such as hydroxyl or sulphydryl, or with a metal atom in the active site or a distinct allosteric site.

TLS Online TPP Program

#Id: 8550

#Unit 1. Molecules and their Interaction Relevant to Biology

diisopropylphosphofluoridate, reacts with a serine OH group in the active site of esterases such as acetylcholinesterase/chymotrypsin, whilst the organomercury compound p-hydroxymercuribenzoate reacts with a cysteine group, in both cases resulting in covalent bond formation and enzyme inhibition.