CBSE Class 12 Chemistry Chapter 16: Chemistry in Everyday Life - NCERT Solutions

Drugs are classified in various ways to organize the vast number of available medicines and to understand their properties and applications better. The main reasons for classification are:

1. On the basis of pharmacological effect: This classification helps doctors by providing a comprehensive list of drugs available for treating a specific ailment or condition, making treatment selection easier.
2. On the basis of drug action: This method categorizes drugs based on how they affect a particular biochemical process within the body. It's crucial for understanding the mechanism of action at a molecular level.
3. On the basis of chemical structure: Grouping drugs by their chemical structure helps identify similarities in their molecular frameworks. Drugs with similar structures often exhibit similar pharmacological activities, aiding in the development of new drugs.
4. On the basis of molecular targets: This classification is particularly useful for medicinal chemists. It groups drugs that act on the same biological targets (like specific enzymes or receptors), providing insights into their mechanism of action and facilitating drug design.

In medicinal chemistry, drug targets refer to the specific biological molecules within an organism that are essential for the progression of a disease. These targets are typically key molecules involved in vital metabolic pathways or cellular processes that, when disrupted, lead to a disease state. Common examples of drug targets include macromolecules such as carbohydrates, proteins, lipids, and nucleic acids.

Medicinal chemists design drugs to interact with these target molecules. The drug binds to the target, often at its active site, to either inhibit or enhance its function, thereby correcting the biochemical imbalance and treating the disease.

The primary macromolecules that are commonly chosen as drug targets in medicinal chemistry are:

• Carbohydrates
• Lipids
• Proteins
• Nucleic acids

These molecules play crucial roles in cellular functions and disease processes, making them ideal sites for drug intervention.

Medicines should not be taken without consulting a doctor due to several critical reasons:

• Specificity of Action: A single drug molecule can often bind to multiple types of receptor sites in the body, not just the intended one. Binding to unintended sites can lead to adverse or toxic effects.
• Dosage Sensitivity: Most medicines are designed to be effective within a specific dosage range. Taking higher doses than recommended can result in toxicity and harmful side effects, potentially making the medicine poisonous.
• Individual Variability: People respond differently to medications based on their genetics, health status, and other factors. A doctor can assess these individual factors to prescribe the most appropriate and safe medication and dosage.

Therefore, professional medical advice is essential to ensure the safe and effective use of medicines.

Chemotherapy is defined as the use of chemical agents for therapeutic purposes. This broad term encompasses the application of chemicals in the diagnosis, prevention, and treatment of diseases. A common example is the use of specific drugs to combat infections or cancer.

Drugs bind to the active site of enzymes through various types of intermolecular forces. These forces are responsible for the specific and often reversible binding of the drug to the enzyme. The forces involved can include:

1. Ionic bonding: Electrostatic attraction between oppositely charged ions.
2. Hydrogen bonding: Attraction between a hydrogen atom bonded to a highly electronegative atom (like O or N) and another electronegative atom.
3. Dipole–dipole interaction: Attraction between the positive end of one polar molecule and the negative end of another.
4. van der Waals force: Weak, short-range attractive forces between nonpolar molecules or parts of molecules.

Antacids and antiallergic drugs do not interfere with each other's functions because they target different biological processes and molecules, even though both might relate to histamine in some way. Here's a breakdown:

• Antiallergic drugs (Antihistamines): These drugs work by blocking the action of histamine at its specific receptors. Histamine is a chemical released during allergic reactions that causes symptoms like itching, swelling, and inflammation. Antihistamines prevent histamine from binding to these receptors, thus reducing allergic symptoms.
• Antacids: Antacids are used to neutralize excess acid in the stomach. They work by reacting with hydrochloric acid (HCl) in the stomach to reduce its acidity. While histamine does play a role in stimulating stomach acid production (histamine H2 receptors), antacids do not directly block histamine receptors. Instead, they chemically neutralize the acid already present.

Therefore, because antacids neutralize stomach acid and antihistamines block histamine receptors, they operate through distinct mechanisms and target different sites, preventing interference with each other's functions.