Enzymes Definition and Function
Introduction
There are thousands of chemical reactions taking place in the body of a living organism. The sum of all these chemical reactions is called metabolism.
These reactions must take place at a high speed to sustain life. A special group of chemicals responsible for facilitating and speeding up these reactions are called enzymes. Enzymes are mostly proteins in nature and are coded by genes.
They are large groups of chemicals that catalyze almost all metabolic reactions in the cell and other parts of the organisms g., the digestive tract.
The term enzyme was coined from the Greek word "leavened" or "in yeast". The first enzyme was discovered by Payen and Persoz from germinating barley seeds in 1833 and named diastase. The term enzyme was introduced by Wilhelm Kuhne in 1877.
Enzymes are "the thermolabile biocatalyst" proteins in nature, specific in function, and coded by DNA. They work inside or outside of the cell. The substance on which the enzyme acts is called substrate which is usually much smaller than the enzyme. When an enzyme combines with substrate it forms an enzyme-substrate complex.
After the enzyme-substrate reaction product is formed the enzyme itself remains unchanged which can be used again for another substrate. Most enzymes are protein in nature, although a few are catalytic RNA - molecules called ribozymes, that can catalyze specific substrates in a similar way as proteinaceous enzymes.
3.1 Structure of Enzymes
Structure of globular pro proteins. The sequence of amino acids specifies the structure of the active site which determines the catalytic activity of the enzyme. An enzyme may have one or more active sites. The active site of the enzyme consists of two parts i.e.,
- Binding site where substrate attaches.
- The catalytic site where the catalysis of the substrate takes place.
The catalytic site is a very small portion comprised of (2 to 12) amino acids. Chemical Nature of enzymes.
Enzymes:
Most enzymes are proteins, so each has its own specific structure, which is required for its proper functioning. A complete functional enzyme is called a holoenzyme. The holoenzyme consists of two parts
- Apoenzyme: It is the proteinaceous part of an enzyme.
- Cofactor: It is a non-proteinaceous part of an enzyme.
Apoenzyme + Cofactor = Holoenzyme.
Some enzymes are only composed of protein i.e., no cofactors are attached to the theme. g. lipase.
Physical Nature of Enzymes:
Enzymes have relatively high molecular weights e.g., the molecular weight of peroxidase is 40,000 Daltons or 40 KDa and catalase 250 KDa approximately. Enzymes due to their proteinaceous nature may denature in high temperatures.
The enzymes form a colloidal suspension in the cytosol, therefore, at low temperatures, their activity may decrease or stop. High fever is harmful to the body because enzymes may denature at high temperatures.
Catalytic Characteristics of Enzymes:
Being catalysts, enzymes show the following characteristics.
- They are very efficient in function e.g., one enzyme may catalyze 100000 substrates in one second. (The unit is called one turnover number).
- Enzymes need specific temperatures for their proper functioning. So drinking cold water during meals is medically wrong.
- Enzymes need specific pH for their proper functioning.
- Enzymes may be studied in living cells (in vivo) or outside living cells i.e., in glassware (in vitro).
- Most enzymes need co-factors for their functioning.
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