hyllokoid membrane These molecules transfer this energy to ATP (Adenosine triphosphate) and other energy carrier molecules. These are diffused into stroma. This energy Is utilized in the formation of sugar compounds by the combination of CO... in this 

way chloroplasts are considered as energy converting organella. 

(vi) Peroxisome: These are very small bodies surrounded by single membrane. The peroxisome 

secrete enzyme which transfers Hydrogen atom to Oxygen to form hydrogen peroxide (H,O,). It is a toxic compound which is immediately converted into water by catalase 

enzyme. Peroxisomes are found in the cells, which metabolize alcohol, for example in liver 

and kidney cells. They take part to destroy the toxic effect of alcohol. 

Peroxisomes also produce other enzymes such as peroxidase, glycolic acidokidase etc. The peroxisomes are also present in yeast, protozoa and many cells of higher plants. In plants they take part in catabolic and anabolic processes. 

(vii) Glyoxysomes: These are microbodies, covered by single membrane. These are usually found in 

plant cells; The glyoxysomes secrete enzymes which take part to activate the molecules of photosynthesis and respiration by fatty acid oxidation, especially in seedlings. They secrete enzymes, which metabolize the oxidation of stored fatty acids to provide energy for the formation of a new plant. These organella are produced only for a short period #7 

the germination of lipid containing seeds. (viii) Cytoskeleton: This is a network of fibrous protein, found in three-dimensional structure, fills “ 

cytoplasm of a cell. Cytoskeleton helps incell division, mitosis, meiosis, cytokinesis, wall formation; It also maintains the cell shape and differentiation of cells to 

THE ENZYMES 

‘ , Enzymes are the organic protieneous substances which catalyse chemical 

reactions in the living organismst These are considered as bio-catalysts. They mcrease thé rate of chemical reaction but are not consumed in the process. 

The term enzyme was used by a Scientist, Friedrich Wilhelm Kuhne in 1878. 

Wharacteristics of Enzymesy (~~ (6) G) _ oH ecay 

iy Enzymes are made up of proteins. ‘They are big molecules with higher molecular weight. — 

- 

(ji) They can react with both acidic and alkaline substances due to the presence of proteins. 

(ili) In a biochemical reaction only a small amount of enzyme is required as compared to the substrate. 

\ - (iv) (EAzymes are not consumed during the reaction. They remain unaffected and can be ~~ used again and again 

(v) The enzymes catalyse only specific reactions, that is, each individual enzyme is restricted in its catalytic activity to one particular reaction or one group of related chemical reactions. 

(v_ heir activities can be accelerated by certain ions or salts, called activator, such as Ni, Mn, Mg, Cl etc. 

(vii) They do not initiate the reaction, but only increase its rate by lowering the energy of activation. < 

wit) Some enzymes contain a non-proteineous part, called Prosthetic group. 

pd When many different enzymes catalyse the same chemical reaction, they are known as isoenzymes. ,