John Hay
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Genetics of Disease (Medical Interventions)
Unit 1: Unit 1.2 Antibiotic TreatmentMI 1.2Culturing

Explain Antibiotic Mechanism

Use culture and antibiotic evidence to explain antibiotic mechanism.

Builds on (2 levels back)inferred · high confidence
  • Aseptic culture technique: Culture results need uncontaminated samples.
  • Antibiotic selection pressure: Drug exposure can favor resistant bacteria.

Prerequisites are inferred: pending teacher review.

Re-learn the skill with worked practice and clear examples.

Explain the mechanism: which bacterial part each antibiotic blocks, using a labeled cell.

Step 1: Label the targets
The cell wall is built from peptidoglycan; the ribosome builds proteins. Different drugs hit different parts.
Labeled bacterial cell showing the cell wall (peptidoglycan) on the outside and a ribosome inside, the two parts antibiotics commonly target.
Step 2: Match drug to part
Penicillin blocks cell-wall synthesis. Tetracycline blocks the ribosome so the cell cannot make proteins.
Step 3: Name the limit
A drug only works if the bacterium actually has the part the drug attacks.
Practice

Penicillin blocks the building of the bacterial cell WALL. Using the labeled cell, which statement best explains how penicillin kills the bacterium?

Reviewed
Labeled bacterial cell showing the cell wall (peptidoglycan) on the outside and a ribosome inside, the two parts antibiotics commonly target.
  1. A.It stops the cell wall from forming, so the cell cannot hold its shape and bursts
  2. B.It feeds the bacterium so it grows too large
  3. C.It changes the bacterium's DNA into human DNA
  4. D.It cools the bacterium until it freezes
Show the worked solution ▾

Answer: A. It stops the cell wall from forming, so the cell cannot hold its shape and bursts

  1. Step 1: Find the target on the figure: Penicillin acts on the cell wall (peptidoglycan).
  2. Step 2: Explain the effect: No wall = no support = the cell bursts.

Why it's right: Penicillin blocks cell-wall (peptidoglycan) synthesis, so the bacterium loses its support and bursts.

Why the others miss:
  • B: Penicillin does not feed bacteria.
  • C: Antibiotics do not convert bacterial DNA into human DNA.
  • D: Antibiotics do not work by freezing cells.

Aligned to Culturing · reading level ~grade 9

Where you'd see this
  • In Unit 1.2 Antibiotic Treatment, this skill turns class evidence into a result another person can check.
Careers that use this
Microbiologist: Uses explain antibiotic mechanism to make a decision from evidence without overclaiming.
Video library
Watch: Explain Antibiotic Mechanism
Antibiotics - Mechanisms of Action, Animation
Alila Medical Media · ~4 min
Guided notes

Fill these in as you work through the lesson.

Big idea: An antibiotic kills bacteria by blocking one specific bacterial part the cell needs to survive.
Key terms: write the meaning
  • Cell wall (the bacterial layer made of ____ that penicillin blocks from forming):  
  • Peptidoglycan (the material the bacterial cell ____ is built from):  
  • Ribosome (the part that builds ____, blocked by drugs like tetracycline):  
  • Mechanism of action (the exact part of the bacterium a drug ____):  
The rule

An antibiotic only works if the microbe has the   the drug attacks, which is why antibiotics do not work on  .

Check yourself
  1. What part of the bacterium does penicillin block? 
  2. What happens to a bacterium that cannot build its cell wall? 
  3. Why does a missing target explain why antibiotics fail against viruses? 
Work one example

A drug blocks the bacterial ribosome. Explain, step by step, why the bacterium cannot make proteins and what that does to the cell, then say whether the same drug would help a viral infection.