The fit between the substrate and the active site of the enzyme is exact.
Like a key fits into a lock very precisely.
Enzyme-substrate complex is formed.
Products have a different shape from the substrate.
Products are released from the active site, leaving it free for another substrate molecule.
Lock and Key Diagram
Diagram showing the enzyme, substrate, active site, enzyme/substrate complex, and products.
Explanation of Enzyme Specificity and Denaturation
Explains enzyme specificity.
Explains the loss of activity when enzymes denature.
Enzyme denaturation: The process by which an enzyme’s structure is changed, and the active site loses its shape, thereby disabling the enzyme from functioning.
Properties of Enzymes
Made of protein, from amino acids produced by digestion or the chemical breakdown of other proteins.
Biological catalysts, not changed by the reactions they speed up, and can be used repeatedly.
Specific: Only one particular enzyme will work with one particular substrate.
Properties of Enzymes (Continued)
Temperature sensitive: Enzymes are denatured or inactivated by excess heat because they are protein. They work best at an optimum temperature.
Sensitive to pH (degree of acidity and alkalinity of a medium). They work best at an optimum pH.
Can be inhibited by poisons such as arsenic and cyanide.
Require moisture to operate, hence found inside our cells.
Factors Affecting Enzymes
Enzymes work best under certain conditions and are affected by:
Enzyme concentration
Substrate concentration
pH
Temperature
Inhibitors
When measuring one factor, keep all other factors constant.
The Effect of Temperature
Heating increases the kinetic energy of molecules.
Increased kinetic energy of the enzyme increases molecular motion.
This raises the chances of the enzyme colliding with a substrate.
The Effect of Temperature (Continued)
All enzymes have an optimum temperature that promotes maximum activity.
If the enzyme’s temperature is increased above its maximum, the enzyme becomes denatured, and enzymatic activity is lowered, potentially stopping.
The Effect of Temperature (Continued)
If the temperature becomes too low or cold, enzymes become inactivated but NOT denatured.
They can become activated again once an appropriate temperature is reached.
Temperature Scale and Enzyme Activity
Graph showing enzyme activity versus temperature.
Optimum temperature marked.
Denaturation point indicated.
The Effect of Temperature: Specific Examples
For most enzymes, the optimum temperature is about 30°C.
Mammalian enzymes tend to have a temperature range between 37-40°C.
Cold-water fish enzymes denature at 30°C.
Some bacteria have enzymes that withstand very high temperatures between 70-100°C.
Most enzymes are fully denatured at 70°C.
The Effect of pH
Different enzymes work at different pH conditions.
Under constant temperature and other conditions, most enzymes function efficiently over a narrow pH range.
If the pH is increased or decreased below an enzyme’s pH range, the enzyme activity will decrease.
When pH increases, this means alkalinity increases, and so does the concentration of hydrogen ions.
The Effect of pH (Continued)
Extreme pH levels will produce denaturation.
The structure of the enzyme is changed as the active site is distorted, and substrate molecules will no longer fit.
At extreme pH values, changes in the charges on substrate molecules will also occur.
This change will affect the binding of the substrate with the active site.
pH Scale
Diagram of the pH scale, ranging from strong acid to strong alkali.
pH values from 1 to 14.
The Effect of pH on Enzyme Activity Graph
Graph showing rate of reaction versus pH.
Optimal pH for pepsin (stomach enzyme) and trypsin (intestinal enzyme) are marked.
pH of the Alimentary Canal
Mouth: Slightly alkaline to neutral.
Stomach: Very acidic; pH 2 (dilute hydrochloric acid).
Duodenum: Very alkaline (bile).
Ileum: Alkaline.
Enzyme Inhibition
An inhibitor is a small molecule or chemical which reduces or stops the rate of the activity of an enzyme.
Inhibitors help to regulate enzyme activity.
Many drugs and poisons act as enzyme inhibitors.
Example: Cyanide inhibits an enzyme involved in respiration.
Enzyme Concentration
If other conditions are kept constant and substrate concentration is maintained at a high level, the rate of reaction is proportional to the enzyme concentration.
Substrate Concentration
The rate of an enzyme reaction increases with increasing substrate concentration for a given enzyme.
However, there comes a point when no increase in substrate concentration will cause a significant increase in enzyme reaction rate.
Faster reaction but it reaches a saturation point when all the enzyme molecules are occupied.
Substrate Concentration Explanation
At high substrate concentrations, the active sites of the enzyme molecules are occupied with substrate.
Therefore, a substrate would have to wait for a reaction to complete and the products to leave the active site before it can enter into the active site of the enzyme.
Catalase
An enzyme found in animal and plant cells.
Detoxification is one of the liver's functions.
Catalase is a natural enzyme found primarily in the liver of animals.
It splits hydrogen peroxide, which is toxic to cells, into harmless oxygen and water.
Needed to speed up the breakdown of hydrogen peroxide.
Breaks it down to oxygen and water.
Word equation: Hydrogen Peroxide -> Oxygen + Water
Amylase
Found in saliva and in the pancreas.
Break down enzyme.
Breaks starch down to maltose.
Word equation: Starch -> Maltose
More About Specificity
Amylase will only breakdown starch.
Catalase will only breakdown hydrogen peroxide.
Amylase will NOT breakdown hydrogen peroxide.
Catalase will NOT breakdown starch.
Are specific for what they will catalyze.
Are Reusable.
End in –ase (Sucrase, Lactase, Maltase).
Examples of Digestive Enzymes in the Alimentary Canal
Lipase: Breaks down fat to glycerol and fatty acids. Produced in the pancreas and small intestine.
Protease (e.g., pepsin, trypsin): Breaks down proteins to amino acids. Produced in the stomach, pancreas, and small intestine.
Carbohydrase (e.g., Maltase, Lactase, Sucrase): Breaks down carbohydrates to simple sugars. Produced in the small intestine and pancreas.
Salivary amylase: Breaks down polysaccharides to maltose. Produced in salivary glands.
Pancreatic amylase: Breaks down polysaccharides to maltose. Produced in the pancreas.
Catalase: Breaks down toxic hydrogen peroxide to water and oxygen. Produced in most tissues.
Uses/Applications of Enzymes
Enzymatic browning common in:
Fruits (Apples, pears, peaches, apricots, and bananas)
Vegetables (Potatoes, lettuce, brinjal)
Cereals (wheat flour, rice)
Sea foods (shrimps, spiny lobsters and crabs)
Uses/Applications of Enzymes: Buzzle.com
Substitutes for commercially produced meat tenderizer powder:
Meat mallet
Papaya paste
Pineapple juice
Uses/Applications of Enzymes: Laundry Detergent
Enzymes used in laundry detergent for stain removal.