enzymes

enzymes

• Proteins that function as biological catalysts are called enzymes.
• A catalyst is a substance that speeds up a chemical (metabolic) reaction.  
• They are composed of C, H, O and N. Sulphur (S) may also be present.

• The function of proteins is determined by their amino acid composition as well as their shape.
• Enzymes control cellular reactions. 
• Reactions that break down substances and release energy are called catabolic reactions e.g respiration and digestion.  
• Another reaction is anabolic reactions that build larger, more complex, molecules from smaller ones e.g Photosynthesis and muscle growth from amino acids.
• Enzymes are folded in globular shapes. 

Enzyme Action

• The enzyme’s shape enables it to receive only one type of molecule; that molecule that will fit into it’s shape. 
• The place where the substance fits into the enzyme is called the active site and the substance that fits into the active site is called the substrate.
• Enzyme action occurs when the enzyme and substrate collide. 
• During the collision the substrate slots into the active site of the enzyme. 
• Collisions happen because of the rapid random movement of molecules.
• When the substrate joins with the enzyme the entire structure is called the enzyme-substrate complex. 
• The substrate becomes changed by the enzyme’s action and is then releases as the product. The enzyme is then free to join another substrate.

Induced Fit Theory

• The enzyme’s active site has a shape closely complementary to the substrate. 
• The substrate locks into the active site of the enzyme. 
• The active site alters its shape holding the substrate more tightly and straining it.
• An enzyme-substrate complex is formed. 
• The substrate undergoes a chemical change and a new substance, product, is formed.
• The product is released from the active site. 
• The free unaltered active site is ready to receive a fresh substrate. 

Different Types Of Enzymes

• lactase – breaks down lactose (milk sugars)
  

• diastase – digests vegetable starch
• sucrase – digests complex sugars and starches
  
• maltase – digests disaccharides to monosaccharides (malt sugars)
  
• glucoamylase – breaks down starch to glucose
  
• protease – breaks down proteins found in meats, nuts, eggs, and cheese
  
• lipase – breaks down fats found in most dairy products, nuts, oils, and meat
  
• cellulase – breaks down cellulose, plant fibre; not found in humans

FACTORS THAT AFFECT ENZYME ACTIVITY

Temperature

• At 0°C enzyme action is low because the movement of molecules is low. 
• This causes the collision frequency between enzyme and substrate to be low. 
• Increasing the temperature speed up the movement of molecules and thus the collision frequency increases therefore enzyme action increases. 
• Human bio enzymes work best at 37 degrees Celsius. 
• As the temperature raises the shape of the enzyme changes and the enzyme becomes denatured. 
• Temperature above 50 degrees Celsius will denature most human enzymes.

Factors that affect Enzyme Activity

pH

• Most enzymes work best at a pH of 6-8. 
• When the pH is outside this range the enzyme will lose its shape and become denatured. 
• The ideal (optimum) pH for most enzymes is 7.

ENZYME CONCENTRATION

• As the concentration of an enzyme increases the rate of reaction also increases, provided that the substrate is in excess.

Factors that affect Enzyme Activity

SUBSTRATE CONCENTRATION

• At low concentration of substrate an increase in concentration will cause an increase in the rate of reaction. 
• However, once the concentration is such that all the active sites of the enzyme are constantly in use then further increase in substrate concentration will have no effect on the rate of reaction.

Temperature

pH

Substrate Concentration

General Effects Of Enzymes

• Enzymes lower the activation energy. 
• This is the energy input needed to bring about the reaction. 
• Enzymes enable the reaction to occur with less energy than would be needed if the enzyme were not present.
• Regulate the thousands of different metabolic reactions in a cell and in the organism.
• The activity of a cell is determined by which enzymes are active in the cell at that time.
• Cell activity is altered by removing specific enzymes and/or synthesising new enzymes.

INHIBITORS

• Enzyme inhibitors are molecules that interact in some way with the enzyme to prevent it from working in the normal manner. 
• Poisons and drugs are examples of enzyme inhibitors. 

Immobilised Enzymes

• Immobilized enzymes are enzymes which may be attached to each other, to insoluble materials, or enclosed in a membrane or gel. 
• This can provide increased resistance to changes in conditions such as pH or temperature. 
• It also allows enzymes to be held in place throughout the reaction, following which they are easily separated from the products and may be used again.

TYPES OF IMMOBILISATION

• Adsorption: In this method the enzyme is attached to a support. Supports can be ceramics, glass, or plastics.
• Membrane Enclosure: In this method the enzyme is enclosed in a porous membrane.
• Gel entrapment: The enzymes are held in a gel. Sodium alginate is a common gel used. The gel allows the substrate to enter and the product to leave.

Immobilise Enzymes

ADVANTAGES OF IMMOBILISATION

• It makes for easier purification of the product as the separation of the enzymes from the products is easily accomplished.
  
• It is easy to recover and recycle the enzymes. 
• This leads to a more economical process.
  
• The enzymes remain functional for much longer as it is a gentler process.

USES OF IMMOBILISED ENZYMES

• Fructose derived from glucose: Fructose is sweeter than glucose and is used in soft drinks and other sweet products.
  
• Antibiotics: Enzymes are used to change penicillin into new, wider used, antibiotics.
  

Sewage Treatment: Instead of bacteria enzymes can be immobilised and used.