What is Enzyme Specificity – Types and Examples: 

What are Enzymes?

• Enzymes are proteins that catalyze thousands of chemical reactions in the body without changing themselves. 
• A cell can contain close to three thousand enzymes. 
• No vitamins, minerals, or hormones work without enzymes. And some enzymes only work together with a mineral or vitamin. That part is called a coenzyme.
• They are biocatalysts.
• Enzymes play a much more important role in our lives than we can even imagine. Our body alone contains roughly 3,000 species. Without enzymes, basically, no chemical reaction would take place in our body.
• Some enzymes are used for digestion, while others circulate throughout the body and perform important tasks such as producing hormones, regulating glandular secretions, balancing pH levels, producing cellular energy, and destroying invaders in the body.

Enzyme Specificity Definition:

• Enzyme specificity is defined as the ability of an enzyme to select an exact substrate from a group of the same chemical molecules converting it into its products.

• Enzymes have the characteristic of acting only on specific substances and causing specific chemical reactions this is known as the specificity of the enzyme.

What is Enzyme Specificity?

• The specificity of an enzyme refers to the selectivity of an enzyme to a substrate.
• Enzymes have an extremely specific action similar to chemical catalysts they catalyze well-defined reactions.
• The high specificity of the action of enzymes is one of the most important features of living matter.
• The action of enzymes is based on the complementarity of the structure of the substrate and the active center of the enzyme.
• The specificity of substrate binding varies greatly between enzymes. Some enzymes can catalyze a reaction involving only one substrate, while others can catalyze reactions involving several chemically related substances.
• Several enzymes have two or even three catalytic functions and act on various substrates that differ greatly in composition and structure.
• The specificity of the action of enzymes is determined by the fact that they have a special amino acid sequence, which determines the conformation of the active center that interacts with the components of the reaction.

Types of Enzyme Specificity:

The degree of specificity of individual enzymes is quite different from each other. There are the following main types of enzyme specificity.

1. Absolute specificity:

• If an enzyme catalyzes the conversion of only one substrate, then it is known as absolute specificity.
• For example, amylase only acts on starch, Urease breaks down only urea, Arginase only breaks down arginine and Glucokinase only phosphorylates D-glucose.

2. Stereospecificity: 

• Stereoisomeric specificity A enzyme act on only one of the stereoisomers. 
• For example, L-lactate dehydrogenase only acts on L-lactic acid but has no catalytic effect on D-lactic acid.

3. Group specificity: Catalysis of substrates with common structural features, i.e. in the presence of a specific bond or chemical group.

4. Relative group specificity:

• When an enzyme catalyzes the transformation of substrates with some common features this is known as relative group specificity. 
• For example, cytochrome P450 oxidizes only hydrophobic substances.

Frequently Asked Questions on Enzyme Specificity: 

1. What does enzyme specific mean?

Answer: Enzyme specificity is a high selectivity of the action of enzymes, It is based on the complementarity of the structure of the substrate and the active center of the enzyme.

2. What is meant by absolute specificity?

Answer: Absolute specificity: when an enzyme acts on one substrate, it is called absolute specificity. 

3. What models justify enzyme specificity?

Answer: To explain the specificity observed between enzymes and their substrates, Emil Fischer proposed in 1894 that the enzyme-substrate complex would obey a “Lock and Key” model.

4. What is an example of enzyme specificity?

Answer: For example, the lactase enzyme is specific for the degradation of lactose into two sugar monosaccharides, glucose, and galactose. Another example is Protease enzymes act on proteins, Glucokinase, which is an enzyme involved in the phosphorylation of glucose to glucose-6-phosphate.

5. What factors determine the specificity of the enzyme?

Answer: Generally enzymes show their specificity for their substrate and the type of reactions. Various factors such as temperature, pH, concentrations of enzymes, and substrate affect the rate of enzyme-catalyzed reactions. Some enzymes require additional factors for their normal activity.

6. What is the importance of enzyme specificity?

Answer: Enzyme specificity is essential to function enzyme catalyze reactions, not only to maintain the production of metabolic pathways but also to prevent unwanted side reactions at a particularly active site. 

7. What is the difference between enzyme activity and specific activity?

Answer: Enzyme activity is the amount of substrate converted by the enzyme in moles per unit of time and specific activity is the activity of the enzyme per mg of the total enzyme.

8. What are the types of enzyme specificity?

Answer: Absolute substrate specificity – the enzyme catalyzes the conversion of only one substrate. For example, the enzyme urease catalyzes the hydrolysis of urea only. Group substrate specificity – the enzyme catalyzes the transformation of a group of substrates of similar chemical structure.

1. The specificity of the enzyme refers to the________

a) Different cells contain different enzymes

b) an enzyme is a special protein

c) the enzyme has specific selectivity for the substrate

d) The structure of the enzyme is specific

Answer: C

2. Enzyme and substrate complementary to each other such as

a) Pencil & eraser

b) Pen & Paper

c) Lock & key

d) all of the above

Answer: C

3. Which of the following is not a type of specificity?

a) Substrate specificity

b) Reaction specificity

c) Group specificity

d) Stereo specificity

Answer: B

4. Which of the following is not true for the specificity of enzyme action?

a) Specificity refers to the discrimination of an enzyme between two competing substrates

b) Specificity of enzymes lies in both the reaction they catalyze and the substrates on which they act

c) Specificity makes it possible for several enzymes to coexist in the cell without interfering with each other reaction

d) Five types of specificities have been recognized in enzymes

Answer: D

5. The statement about the active center of the enzyme is correct

a) All enzymes have active centers

b) All enzymes have coenzymes in their active centers

c) All enzymes have metal ions in their active centers

d) The essential groups of the enzyme are located in the active center

Answer: A

6. Which of the following is an example of group specificity?

a) Trypsin hydrolyzing peptide linkages involving arginine or lysine

b) Lipase hydrolyzing ester bond of lipids

c) Hexokinase phosphorylating one or more kinds of hexoses

d) L-lactate dehydrogenase will act only on L-lactic acid, and not D-lactic acid

Answer: A

7. Which of these is an example of stereospecificity?

a) L-lactate dehydrogenase will act only on L-lactic acid, and not D-lactic acid

b) D-glucose oxidase acting only on D-glucose and not L-glucose

c) L-amino oxidase acts only on L-amino acids and not D-aminoacids

d) All of these

Answer: D

8. Which of the following is an example of absolute substrate specificity?

a) Glucose to glucose-6-phosphate by glucokinase

c) Lactose to glucose and galactose by lactase

d) Urea to ammonia by urease

d) All of these

Answer: D