Since the pace of biochemical reactions is not so quick in absence of enzymes, thus, the enzymes can be considered as catalysts that speed up the reactions such that the time can be shortened from years to seconds.
Next to catalytic properties, enzymes have also the property to increase the pace of reaction without influencing the chemical equilibrium, hence, the final energy of products is not changed, though the activation energy is reduced for he purpose of increase the rate of reaction.
Hence, the enzymes are catalysts that speed up the rate of reaction by mean of reduction of activation energy and preservation of chemical equilibrium of reactants and products.
Enzymes increase the rate of biochemical reactions that are favored by thermodynamics. Without them, the biochemical reactions of life would be too slow to sustain complex life.
Enzymes are protein molecules which act as biological catalsts ie they speed up the rate of chemical reactions in cells without being used up in the reaction.
There are two types of enzyme controlled reactions:
Degradation (catabolic) when an enzyme breaks down large molecules into smaller ones eg. digestion.
Synthesis (anabolic) when the enzyme builds up larger molecules from smaller ones. eg photosynthesis or protein synthesis.
Enzymes are specific, which means each enzyme only catalyses one reaction. This is because the enzyme molecule is folded in a paticular shape with a portion called an active site to which only the correct substrate molecule can attach, much like a key in a lock.
E= Enzyme , S = Substrate, ES = Enzyme /Substrate complex , P = Product(s)
E + S ---> ES ---> P + Unaltered E
Like all proteins, enzyme action is determined by their shape. Extremes of temperature and pH distorts the shape and the substrate can no longer fit in the active site, so the enzyme will no longer work, it is said to be denatured. This is a permanent change. The Temperature that an enzyme works best is called the Optimum eg 37oC for human enzymes.