Biology (0610) | Drugs

Welcome to Chapter 15: Drugs!

Hello Biologists! In this important chapter, we dive into the world of drugs—not just the medicinal kind, but any substance that changes how your body works chemically. Understanding drugs is vital for making informed health decisions and appreciating the power and limitations of modern medicine, especially when dealing with diseases.

Don't worry if this seems like a small chapter; the concepts here are crucial, particularly the section on antibiotics and resistance, which frequently appears in exams!

1. Defining a Drug (Core 15.1.1)

What Exactly is a Drug?

In biology, a drug has a very specific meaning. It is:

A substance taken into the body that modifies or affects chemical reactions in the body.

This definition covers a huge range of substances, from common medicinal products like paracetamol (painkillers) to recreational substances like caffeine or alcohol.

• Modify or Affect: This means the drug changes the normal rate or path of a reaction. For instance, some drugs might speed up a reaction, while others might block it completely.
• Analogy: Think of your body's chemical reactions as a complex machine. A drug is like a specific tool designed to fit into one part of that machine (a receptor or enzyme) to either turn it on, slow it down, or shut it off entirely.

2. The Use and Power of Antibiotics (Core 15.1.2 & 15.1.4)

What are Antibiotics?

Antibiotics are a class of drugs used specifically for the treatment of bacterial infections. They are one of the most successful medical developments in history, saving countless lives.

How Antibiotics Work (The "Bacteria Busters")

Antibiotics target specific features found in bacteria but not in human cells. This selective action allows them to kill the pathogen without harming the host significantly.

Common ways they work include:

1. Attacking the Cell Wall: Many antibiotics stop bacteria from building or repairing their strong cell walls. Since human cells do not have cell walls, this is safe for us.
2. Interfering with Protein Synthesis: They can stop the bacterial ribosomes from making proteins needed for growth and reproduction.

Antibiotics vs. Viruses (Core 15.1.4)

This is a crucial distinction and a very common exam point!

State that antibiotics kill bacteria but do not affect viruses.

Why don't they work on viruses?

• Viruses are not cellular organisms. They do not have cell walls, ribosomes, or their own metabolic machinery.
• Instead, viruses invade our cells and use the host cell's machinery (like our ribosomes) to multiply.
• Since antibiotics target bacterial structures (like their cell wall), they are ineffective against viruses.
• Real-World Example: If you have the common cold (caused by a virus), taking an antibiotic will do nothing to cure it.

3. Antibiotic Resistance: The Evolution Problem (Core 15.1.3 & Supplement 15.1.5)

The Threat of Resistance (Core 15.1.3)

Unfortunately, some bacteria have developed the ability to survive antibiotic treatment.

State that some bacteria are resistant to antibiotics which reduces the effectiveness of antibiotics.

Resistance happens when the antibiotic can no longer kill the targeted bacterium. This means treatments fail, infections last longer, and diseases can spread further.

The Mechanism: How Bacteria Become "Superbugs"

This process is a prime example of natural selection in action (a concept you meet again in Chapter 18):

1. Variation: In any large population of bacteria, there is natural variation. Due to random mutation, a few bacteria might have a gene that makes them slightly resistant to a particular antibiotic.
2. Selection Pressure: When the antibiotic is used, it acts as a selection pressure. It kills all the normal, non-resistant bacteria.
3. Survival: Only the few resistant bacteria survive the treatment.
4. Reproduction: These survivors then reproduce rapidly (as bacteria multiply very quickly), passing the resistance gene on to all their offspring.
5. Result: The entire bacterial population becomes resistant, and the antibiotic is now useless against that infection. These highly resistant types are often called superbugs.

Case Study: MRSA (Supplement 15.1.5)

The syllabus specifically mentions MRSA (Methicillin-resistant Staphylococcus aureus).

MRSA is an example of a bacterium that has developed resistance to many common antibiotics, making it very difficult to treat, particularly in hospital settings.

Limiting the Development of Resistance (Supplement 15.1.5)

We can slow down the natural selection process that leads to resistance.

Explain how using antibiotics only when essential can limit the development of resistant bacteria such as MRSA.

If we use antibiotics unnecessarily, we increase the selection pressure, giving resistant bacteria more opportunities to survive and multiply.

To conserve the effectiveness of current antibiotics, doctors and patients must adhere to strict guidelines:

• Diagnosis First: Antibiotics should only be prescribed when a doctor confirms a bacterial infection (not a viral one like the flu).
• Completing the Course: Patients must finish the entire course of medication, even if they feel better quickly. Stopping early leaves the slightly tougher bacteria alive, increasing the chance of resistance developing.
• Agriculture Control: Reducing the use of antibiotics in farming to prevent resistance genes from developing in animals and transferring to humans.