Structure of Chymotrypsin, a protease enzyme which is active in the duodenum.
Enzymes are biological catalysts. A catalyst is a substance which speeds the rate of reaction but remains unchanged in the reaction. Catalysts reduce the activation energy needed for a reaction. Enzymes are proteins and occur naturally in living biological systems, acting in many metabolic pathways.
The activity of enzymes are affected by pH, temperature, enzyme concentration and substrate concentration. Enzymes have optimum pH and optimum temperatures, at which they experience maximal activity.
How Do Enzymes Work?
Enzymes are highly specific, acting upon a single substrate or group of related substrates. Enzymes have an active site - a small portion of the molecule which is complementary in shape to a portion of the substrate. The substrate binds to the active site of the enzyme forming the enzyme-substrate complex. Strain is induced in the bonds causes them to cleave and the the products leave the active site, leaving it available for further reactions. The reaction of enzymes are reversible.
How Enzymes Work Animation ( You Tube Video )
Enzyme Inhibitors & Co-Factors
Enzymes may be inhibited by inhibitors - molecules which reduce the rate of an enzyme-catalyzed reaction. Inhibitors may be other biological molecules, playing a role in regulation of cell activity. Other inhibitors may be foreign -such as drugs or poisons - and may have a therapeutic or deleterious effect. Inhibitors may be competitive or non-competitive, reversible or irreversible.
Some enzymes require co-factors - non-protein components which bind to the enzyme and modify its active site to its ideal configuration for formation of the enzyme-substrate complex. Co-factors may simply increase the activity of the enzyme or may be necessary for its action.
There are 3 types of co-factors
inorganic ions e.g. the presence chloride ion increases activity of salivary amylase
prosthetic groups (organic molecules which includes vitamins) e.g. Haem and Flavine Adenine Dinucleotide (FAD) containing riboflavin ( vitamine B2)
coenzymes e.g. Nicotinamide Adenine Dinucleotide (NAD), Nicotinamide Adenine Dinucleotide Phosphate (NADP), coenzyme A and Adenosine Tri-phosphate (ATP)
_ Learning Objectives
Explain the properties and functions of enzymes
Explain how various factors - pH, temperature, substrate concentration, enzyme concentration - can affect the rate of enzyme-catalyzed activity
Explain the action of inhibitors - competitive or non-competitive, reversible or irreversible.
Enzyme Experiments
To investigate the effect of substrate concentration on enzyme activity To investigate the effect of enzyme concentration on enzyme activity To investigate the effect of temperature on enzyme activity To investigate the effect of pH on enzyme activity
To investigate the effect of substrate concentration on enzyme activity
To investigate the effect of different pH values on enzyme activity
To investigate the effect of temperature on enzyme activity
Enzyme and substrate pairs commonly used in the for biology experiments are:
Catalase (from raw potato tuber) & hydrogen peroxide
Amylase (commercial preparation) & starch
Sucrase - invertase is the most common sucrase ( commercial preparation) & sucrose.