|
Enzymes (in Greek en = in and zyme = blend) are catalysts and increase the speed of a chemical reaction without themselves undergoing any permanent chemical change. They are neither used up in the reaction nor do they appear as reaction products.
Know what emylase do for the vital activities of our body. Know why it is important to have this enzyme as part of our life?
Amylase
Lipase
Enzymes bind temporarily to one or more of the reactants of the reaction they catalyze. In doing so, they lower the amount of activation energy needed and thus speed up the reaction.
The use of enzymes in the diagnosis of disease is one of the important benefits derived from the intensive research in biochemistry since the 1940's. Enzymes have provided the basis for the field of clinical chemistry.
An enzyme can be a monomeric protein made up of about hundred amino acids or more, or an oligomeric protein consisting of several monomers, different or identical, that act together as a unit.
As with any protein, each monomer is actually produced as a long, linear chain of amino acids, which then folds up in a particular fashion to produce the correct three-dimensional product. The factors that go into ensuring that the chain folds correctly and maintains its shape are complex, and still not completely identified, although the general principles seem to be understood.
An enzyme contains an active site, consisting of the catalytic amino acids and one or more binding sites that bind the substrate(s). Enzymes also frequently have binding sites that serve regulatory functions, which increase or inhibit the enzyme's activity. These typically bind metals or small molecules.
Enzymes can perform up to several million catalytic reactions per second. To determine the maximum speed of an enzymatic reaction, the substrate concentration is increased until a constant rate of product formation is achieved.
Enzymes and Boilogical Reactions
The laws of thermodymatics apply to chemical reactions anywhere in the universe. No reactions can violate the rules of thermodymatics. All reaction must proceed to a level of minimum energy and maximum entropy or have a favorable balance between the two. Enzyme simply increase the rate (rate is equal to the number of reactant molecules converted to product per unit of time) at which spontaneous reactions take place.
Enzymes cannot make a reaction occur that would not proceed spontaneously without the enzyme. The same principle apply to reversible reaction. Enzymes do not alter the equilibrium point of reversible reaction.
Most biological reactions would take place to slow without enzyme for life to exist. The rates would be essentially zero at biological temperatures.
For example the oxidation of glucose to CO 2 and H 2 O is spontaneous and proceeds almost completely in the direction stated. However, without enzymes, glucose oxidation occurs do slowly at physiological temperatures that the rate is essentially unmeasureable.
The increases in rate achieve by enzymes, depending on the enzyme and reaction, range from a minimum of about a million to as much as a trillion times faster than the uncatalyzed reactions at equivalent concentrations and temperatures.
Characteristics of enzymes proteins
Enzymes are protein molecules that are tailored to recognize and bind specific reactants and speed their conversion into products. These proteins are responsible for increasing the rates of all of the many thousand of reaction taking place inside cells.
- Enzymes combine briefly with reactants during an enzyme-catalyzed reaction.
- Many enzymes contain nonproteins groups called cofactors, which contribute to their activity. Inorganic cofactors are all metallic ions. Organic cofactors, called coenzymes, are complex groups derived from vitamins.
- Enzymes are saturated by high substrate concentrations.
- Enzymes are specific in their activity; each enzyme catalyzes the reaction of a single type of molecules or a group of closely related molecules.
- Enzymes are released unchanged after catalyzing the conversion of reactants to Product
- Many enzymes are pH and temperature sensitive
Enzyme cofactors
Many enzymes require the presence of an additional, nonprotein, cofactor. Coenzymes may be covalently bound to the protein part (called the apoenzyme ) of enzymes as a prosthetic group. Others bind more loosely and, in fact, may bind only transiently to the enzyme as it performs its catalytic act.
Protease
Amylase
Lipase
Lactase
|
