Chemistry In Everyday Life Class 12 Notes

Key Definitions for Quick Recall

Drugs (Medicines)

Chemicals of low molecular masses (~100-500 u) that interact with macromolecular targets and produce a biological response.

Chemotherapy

The use of chemicals for therapeutic effect, i.e., treatment of diseases.

Antacids

Chemicals that neutralize excess acid in the stomach and raise the pH to an appropriate level.

Antihistamines

Drugs that counteract the effect of histamine, which causes inflammation and allergic reactions.

Analgesics

Drugs that reduce or abolish pain without causing impairment of consciousness, mental confusion, incoordination, or paralysis.

Antimicrobials

Drugs that kill or inhibit the growth of microorganisms (bacteria, fungi, viruses, etc.).

Antiseptics

Chemicals that prevent the growth of microorganisms or kill them. Applied to living tissues like wounds, cuts, ulcers.

Disinfectants

Chemicals that kill microorganisms but are not safe for application to living tissues. Used on inanimate objects like floors, instruments.

Artificial Sweeteners

Chemical substances that are sweet but contain negligible calories and are excreted unchanged from the body.

Food Preservatives

Chemical substances that prevent spoilage of food due to microbial growth.

Understanding Drug-Target Interaction

Most drugs perform their function by interacting with macromolecular targets in the body. These targets are usually biomolecules like proteins, nucleic acids, lipids, and carbohydrates. Enzymes and receptors are common protein targets.

Enzymes as Drug Targets: Enzymes catalyze biochemical reactions. Drugs can inhibit the catalytic activity of enzymes. They do this by:

1. Competitive Inhibition: Binding to the active site of the enzyme, thus preventing the actual substrate from binding. This is often achieved by drugs mimicking the natural substrate.
2. Allosteric Inhibition: Binding to a different site (allosteric site) on the enzyme, which changes the shape of the active site, making it unable to recognize the substrate.

Receptors as Drug Targets: Receptors are proteins crucial for communication between cells. They are embedded in the cell membrane and have specific binding sites for chemical messengers (like hormones, neurotransmitters). A drug can:

• Agonist: Mimic the natural messenger and activate the receptor, producing a response. For example, some drugs bind to receptor sites and initiate the same action as the natural chemical messenger.
• Antagonist: Bind to the receptor site and inhibit its natural function, blocking the message. This is useful when the natural messenger's action needs to be blocked.

The specificity of drug action arises from the unique structure of the drug that fits into the binding site of a particular macromolecular target, much like a 'lock and key' mechanism. This interaction is usually reversible, involving weak forces like hydrogen bonds, ionic bonds, van der Waals forces, or dipole-dipole interactions.

Key Points to Remember for Exams

• Drugs are classified based on pharmacological effect (e.g., analgesics, antacids), drug action (e.g., enzyme inhibitors, receptor blockers), chemical structure (e.g., sulfonamides), and molecular targets (e.g., lipids, proteins, nucleic acids).
• Popular antacids include Magnesium hydroxide, Aluminium hydroxide, Cimetidine (Tagamet), and Ranitidine (Zantac). Cimetidine and Ranitidine are superior as they prevent acid formation.
• Antihistamines (e.g., Terfenadine/Seldane, Brompheniramine) interfere with the action of histamine by binding to receptor sites where histamine exerts its effect, but they do not affect gastric acid secretion.
• Analgesics are broadly classified into non-narcotic (non-addictive) like Aspirin and Paracetamol, and narcotic (addictive) like Morphine and Codeine. Aspirin is also antipyretic and anti-inflammatory.
• Antibiotics can be bactericidal (kill bacteria, e.g., Penicillin, Ofloxacin) or bacteriostatic (inhibit growth, e.g., Erythromycin, Tetracycline). They can also be broad-spectrum (effective against wide range of bacteria, e.g., Chloramphenicol) or narrow-spectrum (effective against specific types, e.g., Penicillin G).
• Antiseptics (e.g., Dettol, Bithional, Tincture of Iodine, Boric acid) are applied to living tissues. Disinfectants (e.g., Chlorine, Phenols) are applied to non-living objects.
• Phenol acts as an antiseptic at low concentrations (0.2%) and as a disinfectant at higher concentrations (1%).
• Common artificial sweeteners include Saccharin, Aspartame, Sucralose, and Alitame. Aspartame is unstable at cooking temperatures.
• Food preservatives like sodium benzoate, sodium metabisulphite, and common salt or sugar are used to prevent microbial spoilage of food.
• Soaps are sodium or potassium salts of long-chain fatty acids. Synthetic detergents (anionic, cationic, non-ionic) are preferred as they work well in hard water and are stronger cleansing agents.

Antiseptics vs. Disinfectants: A Key Distinction

Worked Examples: Understanding Chemical Applications

• {"title":"Example 1: Antacid Action","description":"Question: Why is Cimetidine considered a better antacid than Sodium Bicarbonate?\n\nSolution: Sodium bicarbonate, while neutralizing excess stomach acid, also makes the stomach alkaline and triggers the production of even more acid. Cimetidine (Tagamet) and Ranitidine (Zantac) are antihistamines that prevent the interaction of histamine with receptor sites in the stomach wall. This prevents the stimulation of acid secretion, thereby controlling acidity more effectively without causing secondary problems."}
• {"title":"Example 2: Artificial Sweetener Properties","description":"Question: Name an artificial sweetener that is unstable at cooking temperatures. Why is this a limitation?\n\nSolution: Aspartame is unstable at cooking temperatures and decomposes, losing its sweetness. This limits its use to cold foods and soft drinks. For high-temperature applications, heat-stable artificial sweeteners like Sucralose or Alitame are preferred."}
• {"title":"Example 3: Analgesic Function","description":"Question: How does Aspirin act as both an analgesic and an antipyretic?\n\nSolution: Aspirin (acetylsalicylic acid) acts as an analgesic by inhibiting the synthesis of prostaglandins, which are compounds responsible for inducing pain. It acts as an antipyretic by lowering body temperature during fever, likely by resetting the body's thermostat in the hypothalamus. It also has anti-inflammatory properties."}

Exam Tip: Mastering This Chapter

This chapter is a goldmine for direct, factual questions. Focus on:

1. Drug Names and Their Classifications: Know specific examples for antacids, antihistamines, analgesics (narcotic/non-narcotic), antibiotics (bactericidal/bacteriostatic, broad/narrow spectrum), antiseptics, and disinfectants.
2. Distinctions: Be clear on the differences between antiseptics and disinfectants, bactericidal and bacteriostatic antibiotics, and synthetic detergents vs. soaps.
3. Functions and Mechanisms: Understand how these chemicals work (e.g., how Cimetidine works as an antacid, or how artificial sweeteners provide sweetness without calories).
4. Application-based questions: Expect scenarios where you need to identify the appropriate chemical for a given situation (e.g., treating an infection, cleaning a floor). Create flashcards for effective memorization!

Practice Questions with Solutions

• Q: Give one example of a broad-spectrum antibiotic and explain why it's called so. A: Chloramphenicol is a broad-spectrum antibiotic because it is effective against a wide range of gram-positive and gram-negative bacteria, rickettsiae, and certain viruses.
• Q: What is the main difference in application between antiseptics and disinfectants? A: Antiseptics are applied to living tissues (e.g., skin, wounds), while disinfectants are applied to inanimate objects (e.g., floors, instruments).
• Q: Name two common artificial sweeteners and state which one is unsuitable for cooking. A: Saccharin and Aspartame. Aspartame is unsuitable for cooking because it decomposes at high temperatures.
• Q: What is the role of BHT (Butylated Hydroxytoluene) and BHA (Butylated Hydroxyanisole) in food? A: BHT and BHA are used as antioxidants in food to prevent oxidation of fats and oils, thereby preventing rancidity and preserving food freshness.

Frequently Asked Questions