3.7.8Additional lessons
Antibiotics — IB Biology HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 7 of 101
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 5What Antibiotics Do
Bacteria differ from human cells in structure and metabolism, and antibiotics exploit those differences.
Definition
- Definition Antibiotics are drugs that kill bacteria or stop them growing, so they are used to treat bacterial infections.
Selective action
- Selective action They block processes that occur only in prokaryotic cells, so human cells are left unharmed.
Cell wall synthesis
- Cell wall synthesis Penicillin prevents bacteria from building their peptidoglycan cell walls, so cells take in water and burst by osmosis.
Protein synthesis
- Protein synthesis Some antibiotics, such as tetracyclines, bind to the 70S ribosomes of bacteria, which differ from the 80S ribosomes of human cells.
Part 2 of 5Why Antibiotics Do Not Work on Viruses
Why Antibiotics Do Not Work on Viruses
No cell structure
- No cell structure Viruses have no cell wall and no ribosomes, so the targets of antibiotics are simply absent.
Host machinery
- Host machinery A virus replicates inside host cells using the host's own enzymes and ribosomes, so drugs that stop it must avoid harming the host.
Antiviral drugs
- Antiviral drugs Antivirals block specific viral steps, for example reverse transcriptase in HIV, and are different from antibiotics.
Colds and influenza
- Colds and influenza These are viral infections, so prescribing antibiotics for them does not help and contributes to resistance.
Part 3 of 5Using Antibiotics Responsibly
1
Doctors identify the likely cause of the infection and decide whether it is bacterial.
2
A suitable antibiotic is chosen, and a narrow spectrum drug is used when the bacterium is known.
3
The patient takes the full course so that all of the bacteria, including those less sensitive to the drug, are killed.
4
Stopping early leaves surviving bacteria that may multiply and carry resistance.
| Property | Bacterial cell | Human cell |
|---|---|---|
| Cell wall | Peptidoglycan present | None |
| Ribosomes | 70S | 80S |
| Antibiotic effect | Growth stopped or cell killed | Little or no effect |
Part 4 of 5Antibiotics in Medicine and Research
Antibiotics in Medicine and Research
Discovery of penicillin
- Discovery of penicillin Fleming noticed that mould growing on a culture plate had cleared the bacteria around it,
- and later Florey and Chain purified the drug for treatment.
Bactericidal or bacteriostatic
- Bactericidal or bacteriostatic A bactericidal drug kills bacteria outright,
- whereas a bacteriostatic drug only stops them multiplying so the immune system can finish the job.
Testing sensitivity
- Testing sensitivity Bacteria are spread on agar with discs of different antibiotics,
- and the clear zone around each disc shows how effective that drug is.
Side effects
- Side effects Antibiotics may cause allergic reactions in some people and may destroy harmless gut bacteria, which can upset digestion.
Part 5 of 5Exam Checklist & Tips
3.7.8 – Key Points for the Exam
- Antibiotic A drug that kills or inhibits bacteria.
- Penicillin An antibiotic that prevents formation of bacterial cell walls.
- Peptidoglycan The polymer that strengthens bacterial cell walls.
- Antiviral A drug that blocks a step in viral replication.
- Broad spectrum An antibiotic effective against many types of bacteria.
Common Mistakes
- Saying antibiotics kill viruses; they work only against bacteria.
- Writing that penicillin works against all bacteria, although some have thick walls or enzymes that break it down.
- Thinking that antibiotics destroy human cells' ribosomes, when the bacterial ribosomes differ in structure.
- Believing that you may stop the course as soon as you feel better.
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