Review Questions

Enzymes:

Proteins that speed up chemical reactions inside living organisms, by minimizing the activation energy are known as enzymes.

Functions of Enzymes:

Enzymes are proteins that catalyze i.e. speed up) biochemical reactions and are not changed during the reaction. In enzymatic reactions, the molecules at the beginning of the process are called substrates, and the enzyme converts them into different molecules, the products. Almost all processes in a cell need enzymes to occur at significant rates.

Characteristics of Enzymes:

1. Almost all enzymes are proteins i.e. they are made of amino acids.
2. Most enzyme reaction rates are millions of times faster than those of comparable uncatalyzed reactions. As with all catalysts, enzymes are not consumed by the reactions they catalyze.
3. Enzymes are usually very specific for the type of reaction and the nature of their substrates
4. The activities of enzymes are determined by a small portion of the enzyme molecule (around 34 amino acids) which is directly involved in catalysis. This catalytic region, known as the active site, recognizes and binds the substrate, and then carries out the reaction.
5. Since enzymes are extremely selective for their substrates and speed up only a few reactions, the set of enzymes made in a cell determines which metabolic pathways occur in that cell.
6. Enzymes can be categorized based on the site where they work i.e., they may be intracellular enzymes (e.g., enzymes of glycolysis working in the cytoplasm) or maybe extracellular enzymes (e.g., pepsin enzyme working in the stomach cavity).

7. The enzyme activity is controlled in the cell in many ways. Enzyme production can be enhanced or diminished by a cell in response to changes in the cell's environment. Enzyme activity can also be regulated by inhibitors and activators. 

8. Some enzymes do not need any additional components to show full activity However, others require non-protein molecules or ions called cofactors for activity.

Types of Cofactors: Cofactors can be either inorganic (e.g. metal ions) or organic (e.g. flavin and heme).

Coenzymes:

If organic cofactors are tightly bound to the enzymes, they are called prosthetic groups, but if they are loosely attached to the enzyme, they are called coenzymes. Coenzymes are small organic molecules that transport chemical groups from one enzyme to another. Some important coenzymes are vitamins (e.g. riboflavin, thiamine, and folic acid).

9. Several enzymes can work together in a specific order, creating metabolic pathways. In a metabolic pathway, one enzyme takes the product of another enzyme as a substrate. After the catalytic reaction, the product is then passed on to another enzyme.

Activation Energy:

The minimum amount of energy required for effective collusion during a chemical reaction is called activation energy.

Significance of Activation Energy:

All chemical reactions require activation energy to break chemical bonds and begin the reaction. The need for activation energy acts as a barrier to the beginning of the reaction.

Reference of Activation Energy in Enzymes:

Enzymes lower such barriers by decreasing the requirement of activation energy of enzymes, reactions proceed at a faster rate Enzymes lower the activation energy in several ways. They do so by:

1. Altering the shape of the substrates and reducing the amount of energy required to complete the transition.
2. Disrupting the charge distribution.
3. Bringing substrate in the correct orientation to react.