Characteristics of enzymes



Properties of Enzymes                             OR                               characteristics of Enzymes:

The common characteristics of enzymes are listed below ___



1): Chemical Nature : 

The enzymes are generally complex macromolecules of globular proteins. Many have additional nonprotein ( inorganic or organic) substances associated with them for their activity .

2): Modecular Weight:

Being protein macromolecules, the enzymes have very high molecular weights. These vary from 6000 for bacterial ferredoxin to 4,600,000 for pyruvate dehydrogenase complex.

 3): Chemical Activity:

The enzymes do not start a chemical reaction but only accelerate it. They may break a large molecules into two smaller molecules, or bring two small molecules together to  form a larger molecule, or transfer whole groups, such as amino groups, or transfer electrons or hydrogen ions from one molecule to another.

4): Changeless Form :

The enzymes combine temporarily with the substrate molecules but are not consumed or changed permanently in the reaction they catalyse. Neither their presence alters the nature and quantity of the end products of the reaction.


5): Reversibility of Reaction: 

The enzymes _ controlled reactions are reversible. The enzymes affect only the rate of the biochemical reaction, not the direction. They can accelerate th reaction in either direction.Lipase, for example, can catalyse splitting of a fat into fatty acids and glycerol as well as synthesis of fatty acids and glycerol into fats. However, reversion may be checked by removing the product of enzymes reaction as quickly as they are formed.


6): High Efficiency:

Most enzymes have high turnover number. A turnor  number of an enzyme refers to the number of molecules of a substance acted upon by one molecule of enzyme per minute. A molecule of the enzyme catalase from cattle liver decomposes 5,000,000 molecules of hydrogen peroxide to water and hydrogen in one minute at 0°C. The turnor number of catalase is, thus, 5,000,000 at 0°C. The turnover number for carbonic anhydrase present in the RBCs is 36 million. The higher the turnover number, the more efficient the enzyme is . High turnover numbers of enzymes explain their remarkable effectiveness even though they occur in a cell in minute quantities. 

   Not all enzymes are fast acting. Some are very slow. LysozymeLysozyme, for example, catalyses one reaction every two seconds. 


 (7): Active Specificity: 

The enzymes are specific in action. An enzymes may catalyze only a particular kind of reaction, or may even act on a particular substrate only. For example, the enzyme lactase catalyzes the hydrolysis of lactose and no other disaccharide. Specificity of an enzymes results from its unique 3__ dimensional shape.

(8) Temperatureb Sensitivity: 

The enzymes are thermolabile,i.e., heart sensitive. They function best at an optimum temperature. The optimum temperature for human enzymes is 35 to 40°C___ close to human body temperature. The enzyme activity decreases with decrease as well as  increase in temperature, and stops at 0°C and above 80°C. The enzymes of bacteria inhabiting springs have an optimum temperature of 70°C or more.


(9) pH Sensitivity:

The enzymes show maximum activity at an optimum pH(6___8) . Their activity slows with decrease and increase in pH till it stops. Pepin,a digestive enzymes in the stomach, works, best at a pH 2. This high acidic pH denatures most enzymes but pepsin is adapted to it.


(10) Team Work:

The enzymes generally work in teams in the cell, the product of one enzymes _ controlled reaction serving as the substrate for the next. In germinating seeds, starch is changed into glucose by two enzymes: amylase and maltase. Amylase splits the starch into the double sugar maltose, which is then broken by maltase into the single sugar  glucose. Eleven different enzymes work sequentially to convert glucose to lactic acid in animal as well as plant cells. 


 ( 11) Destruction by Poisons: 

The enzymes are destroyed by poisons, such as cyanide and iodoacetic acid. Cyanide poisoning is due to the destruction of the respiratory cytochrome enzymes by the cyanide.

What are ribozymes?

Ans: Ribozymes are RNA molecules that function as biocatalysts in modern cells ( Thomad Cech, 1980s,) . The fact disproves the long_ held view that only proteins( enzymes) act as biological catalysis . Ribozymes catalyse synthesis of RNAs: rRNA, tRNA, mRNA ( autocatalysis) and removal of introns from mRNA.






















































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