6o General Botany 



They are important in speeding up all chemical reactions in cells ; 

 without them the chemical changes would be so slow that hfe 

 could not continue. 



Chemists have known for a long time that many reactions can 

 be accelerated by the addition of small quantities of certain sub- 

 stances which do not appear to take any immediate part in the 

 reactions. For example, if we boil cane sugar in pure water, 

 glucose and fructose are formed very slowly. 



C12H22O11 + H2O — ^ C6H12O6 + CeHioOe 



cane sugar water glucose fructose 



If a very small amount of a mineral acid is added, the reaction 

 takes place very rapidly. Substances which accelerate chemical 

 reactions are called catalysts, or catalytic agents. 



All cell processes, including oxidation, take place at ordinary 

 temperatures, often indeed at very low temperatures ; and it 

 would be quite impossible for them to take place so rapidly in 

 the absence of catalytic agents. Enzymes are the catalytic agents 

 of the cell. Many enzymes have been isolated from plant tissues, 

 the best known of which are diastase, used in digesting starch ; 

 lipase, employed in breaking down fats ; and papain, used in 

 digesting proteins. 



Enzymes will be more fully discussed later in connection with 

 digestion, but they are mentioned at this time because of their 

 occurrence in all cells and because they are concerned in all chemi- 

 cal processes that occur in cells. Enzymes not only aid in break- 

 ing down complex substances in cells, but under slightly different 

 conditions bring about the reverse process, the building up of 

 complex substances. They are concerned in photosynthesis, 

 fat synthesis, protein synthesis, and the formation of the many 

 substances described in this chapter. 



Protoplasm. The hving substance of the cell is the most 

 important product made from food. Carbohydrates, fats, and 

 proteins are in some way by the aid of enzymes built into proto- 

 plasm. This process can only be carried on by previously exist- 



