Tour of the Cell: Structure, Function, and Microscopy

Tour of the Cell

Microscopes: Tools for Studying Cells

Microscopes are essential instruments in biology, allowing scientists to observe cells and their structures, which are too small to be seen with the naked eye. There are several types of microscopes, each with unique capabilities.

• Compound Light Microscopes: Use two lenses (ocular and objective) to magnify specimens up to 400X. The total magnification is calculated by multiplying the magnification of the ocular lens by that of the objective lens.

• Electron Microscopes: Use beams of electrons for much higher magnification and resolution than light microscopes.

  • Transmission Electron Microscope (TEM): Passes electrons through thin specimens, achieving up to 200,000X magnification. Used to study internal cell structures.

  • Scanning Electron Microscope (SEM): Scans a thin beam of electrons across the surface of specimens, producing detailed 3D images of surfaces, up to 100,000X magnification.

Example: TEM is used to view the internal structure of mitochondria, while SEM is used to visualize the surface of pollen grains.

Why Study Cells?

Understanding cells is fundamental to biology and medicine. The study of cells has led to major advances, such as the development of antibiotics.

• Antibiotics: Penicillin, discovered in 1920, drastically reduced deaths from bacterial infections. Early antibiotics targeted structures unique to bacteria, such as bacterial ribosomes and enzymes.

• Medical Relevance: Studying cells helps in developing new antibiotics and combating antibiotic-resistant strains.

Example: Penicillin targets bacterial cell wall synthesis, which is absent in human cells, making it effective and safe.

Cell Size and Scale

Relative Sizes of Biological Structures

Cells and their components vary greatly in size, from visible objects like chicken eggs to microscopic structures like ribosomes and viruses.

Structure	Approximate Size	Visibility
Human height	~1.7 m	Visible
Chicken egg	~5 cm	Visible
Plant and animal cells	10–100 μm	Light microscope
Nuclei, mitochondria	1–10 μm	Light microscope
Bacteria	1–5 μm	Light microscope
Viruses	20–300 nm	Electron microscope
Ribosomes	~20 nm	Electron microscope
Proteins, lipids	~1–10 nm	Electron microscope
Atoms	~0.1 nm	Electron microscope

Measurement Equivalents:

• 1 meter (m) = 100 cm = 1,000 mm = $10^6$ μm = $10^9$ nm

• 1 centimeter (cm) = $10^{-2}$ m

• 1 millimeter (mm) = $10^{-3}$ m

• 1 micrometer (μm) = $10^{-6}$ m

• 1 nanometer (nm) = $10^{-9}$ m

Example: Most bacteria are about 1–5 μm in size, while ribosomes are about 20 nm.

Additional info:

• Cells are the basic unit of life, and their study is foundational for understanding all biological processes.

• Advances in microscopy have enabled the discovery of cell structures and functions, leading to major medical and scientific breakthroughs.