Cell Discovery, Theory, and Microscopy: Comprehensive Study Guide

Fundamental Concept of Cell Theory

• Cell Theory serves as the foundational principle for understanding life, asserting that all living organisms are comprised of cells.
• Conceptual analogies:
  • Matter is composed of atoms.
  • Buildings are composed of bricks.
  • Organisms are composed of cells.
• Examples of specialized cells include:
  • Skin cells: Extremely small cells that provide external protection.
  • Photoreceptor cells: Located in the eyes, specialized for light detection.
  • Nerve cells: Characteristically long and thin; designed to receive and transmit information throughout the body.

The Discovery of the Cell

• 1665 - Robert Hooke: An English scientist and physicist often referred to as the "English Father of Microscopy."
  • He examined a thin slice of dried cork tissue using a compound microscope.
  • He observed structure similar to a honeycomb or small chambers.
  • He coined the term "cell" because these chambers reminded him of the small rooms in a monastery.
  • This discovery was published in his work titled Micrographia.
• The birth of the science of cell biology directly paralleled the invention and subsequent improvements of the microscope.

Chronological Development of the Microscope

• 1590: Hans Janssen and his son, Zacharias Janssen, discovered that placing multiple lenses in a tube significantly enlarged objects. Their early instruments were approximately two feet long and very heavy.
• 1609: Galileo Galilei invented a compound microscope utilizing both convex and concave lenses. He was notably the first to record a biological observation (an insect's compound eye) using a crude microscope.
• 1625: Giovanni Faber first used the term "microscope" to describe Galileo's compound microscope.
• 1676: Antonie van Leeuwenhoek, a Dutch microscope maker, became the first to see living cells using a single-lens microscope. He examined blood cells, yeast, insects, and was the first to study protozoa. His instrument provided a magnification of $270 \times$, vastly superior to the contemporary $20 \times$ to $30 \times$ magnifications.
• 1830: Joseph Lister successfully reduced spherical aberrations by combining several weak lenses at specific distances to achieve high magnification without image blurring.
• 1874: Ernst Abbe introduced a mathematical formula correlating resolving power to the wavelength of light, allowing calculation of the theoretical maximum resolution of a microscope.
• 1931: Ernst Ruska and Max Knoll built the first Transmission Electron Microscope (TEM), which uses electrons instead of light to visualize objects as small as an atom's diameter.
• 1932: Frits Zernike invented phase-contrast illumination, enabling the imaging of transparent samples without the need for staining.
• 1942: Ernst Ruska invented the first scanning electron microscope which transmits an electron beam across the surface of a specimen.
• 1957: Marvin Minsky introduced confocal imaging, providing higher resolution than conventional light microscopy.
• 1972: Godfrey Hounsfield and Allan Cormack developed the Computerized Axial Tomography (CAT) scanner for 3D views of internal organs.
• 1978: Thomas and Christoph Cremer developed the first practical confocal laser scanning microscope.
• 1981: Gerd Binnig and Heinrich Rohrer invented the Scanning Tunneling Microscope (STM), capable of visualizing individual atoms at a scale of $2 \times 10^{-10}\,m$ or $0.2\,nm$.
• 1986: Ernst Ruska, Gerd Binnig, and Heinrich Rohrer were awarded the Nobel Prize in Physics for their contributions to microscopy.
• 1992: Douglas Prasher cloned the Green Fluorescent Protein (GFP), revolutionizing fluorescence microscopy by inserting the GFP gene before a stop code to label specific proteins.
• 1993–1996: Stefan Hell pioneered super-resolution microscopy.
• 2008: The Titan 80-300 Cubed electron microscope was installed in Canada, advancing nanotechnology.
• 2010: Researchers at UCLA used a cryo-electron microscope to visualize the atoms of a virus.
• 2014: Eric Betzig, Stefan Hell, and William Moerner won the Nobel Prize in Chemistry for super-resolution microscopes that see matter smaller than $0.2\,\mu m$.
• 2017: Jacques Dubochet, Joachim Frank, and Richard Henderson created a technique for 3D atomic-level protein structures using vitrification (cooling samples to cryogenic temperatures) in an electron microscope.
• 2018: The Titan Krios, a high-end transmission electron microscope, was unveiled by Thermo Fisher Scientific.

Types of Microscopes and Their Mechanisms

• Compound Microscope:
  • Uses two lenses: the objective lens and the ocular lens, mounted on opposite ends of a closed tube.
  • Produces 2D magnified images of tiny specimens.
  • Standard magnification range: $1,000 \times$ to $2,000 \times$.
• Electron Microscope:
  • Illuminates objects in a vacuum using electron beams focused by magnetic fields.
  • No diffraction blurring because electron beams have shorter wavelengths than light.
  • Can magnify objects up to tens of thousands or more than $200,000 \times$ their actual size.
• Scanning Tunneling Microscope (STM):
  • A type of scanning probe microscope.
  • Scans surfaces with an extremely sharp metal point (as narrow as a single atom).
  • Provides precise 3D images of atoms and can be used to trigger chemical reactions.

Anatomy of the Compound Microscope

Mechanical Parts (Support and Adjustment)

• Base: The bottom part that supports the entire instrument.
• Pillar: The part above the base supporting upper components.
• Arm: The curved spine used for safe handling and supporting the body tube.
• Inclination Joint: A pivot point that allows the microscope to be tilted.
• Stage: The platform with an opening where the specimen is placed.
• Stage Clips: Used to hold the slide in place.
• Body Tube: The structural corridor connecting the eyepiece to the revolving nosepiece.
• Draw Tube: The upper sleeve holding the ocular lens.
• Revolving Nosepiece: A rotating turret holding the objective lenses.

Magnifying Parts

• Eyepiece / Ocular Lens: The lens the observer looks through, usually with a magnification of $10 \times$.
• Objective Lenses: The main lenses for magnification. Common powers are:
  • Scanner/Low: $4 \times$
  • Low-Power Objective (LPO): $10 \times$
  • High-Power Objective (HPO): $40 \times$
  • Oil Immersion Objective: $100 \times$

Illuminating Parts

• Mirror/Light Source: Provides illumination for the specimen.
• Condenser: Focuses the light onto the specimen.
• Iris Diaphragm: Regulates the amount of light passing through the condenser.

Principles of Microscopy and Calculations

• Magnification: The ability to make small objects appear larger.
• Resolution: The ability to distinguish two closely placed objects from each other; high resolution clarifies distinct boundaries.
• Total Magnification Formula:
  • $\text{Total Magnification} = \text{Ocular Lens Magnification} \times \text{Objective Lens Magnification}$
• Calculation Examples:
  • Low-Power: $10 \times (Ocular) \times 10 \times (Objective) = 100 \times$
  • High-Power: $10 \times (Ocular) \times 40 \times (Objective) = 400 \times$
• Optical Limit: Laboratory light microscopes typically max out around $2,000 \times$ magnification.

Tenets of Cell Theory

• Foundational Statements (Classical Theory):
  1. All living organisms are composed of one or more cells.
  2. The cell is the basic structural and functional unit of living organisms (reproduction, metabolism, response).
  3. All cells come only from pre-existing cells (credited to Rudolf Virchow).
• Modern Extensions:
  4. Cells carry and pass on hereditary units (DNA) during cell division.
  5. All cells are relatively the same in terms of chemical composition and metabolic activity.
  6. Energy flow (metabolism and biochemistry) occurs within cells.

Cell Physicality: Size, Shape, and Internal Organization

Cell Size

• Humans can see objects as small as $100\,\mu m$ (microns) with the naked eye.
• Human Ova (Egg Cells): Just visible to the human eye.
• Unfertilized Bird Eggs: Typically large enough to be seen without a microscope.
• Bacterial Cells: Range from $1\text{ to }10\,\mu m$ in diameter.

Why Cells Are Small (Surface Area to Volume Ratio)

• As a cell grow, its volume increases by the cube, while surface area increases by the square.
• Efficiency Trend:
  • Size: $2\,cm$ | SA: $24\,cm^2$ | Vol: $8\,cm^3$ | SA/Vol Ratio: $3.0$
  • Size: $4\,cm$ | SA: $96\,cm^2$ | Vol: $64\,cm^3$ | SA/Vol Ratio: $1.5$
  • Size: $6\,cm$ | SA: $216\,cm^2$ | Vol: $216\,cm^3$ | SA/Vol Ratio: $1.0$
  • Size: $8\,cm$ | SA: $384\,cm^2$ | Vol: $512\,cm^3$ | SA/Vol Ratio: $0.75$
• Deduction: As the ratio plummets, the cell cannot efficiently exchange food, water, oxygen, and waste with its environment.

Form Follows Function (Cell Shape)

• Nerve Cells (Neurons): Long with cytoplasmic extensions (axons and dendrites) to transmit impulses over long distances.
• Skin (Epithelial) Cells: Flat architectural layout to cover and protect the body.
• Blood Cells: Capable of changing shape to digest and kill disease-causing germs.

Internal Organization

• Organization is strictly dictated by function. There are approximately 200 different types of cells in the human body.
• Muscle Cells: Packed with heavy concentrations of mitochondria for extreme energy output and contraction.
• Glandular Cells: Contain higher concentrations of ribosomes and Golgi bodies for the production of secretory materials like mucus and hormones.

Questions & Discussion

• Matching Scientists to Contributions:
  • Robert Hooke: Named the "cell" after observing cork.
  • Antonie van Leeuwenhoek: Observed "animalcules"/living cells in pond water.
  • Matthias Schleiden: Concluded all plants are composed of cells (1838-1839).
  • Theodor Schwann: Concluded all animals are composed of cells (1839).
  • Rudolf Virchow: Stated all cells come from pre-existing cells.
• Chronological Ordering Challenge:
  1. Robert Hooke observes empty cork cells.
  2. Antonie van Leeuwenhoek observes microscopic animalcules.
  3. Matthias Schleiden concludes plants are made of cells.
  4. Theodor Schwann concludes animals are made of cells.
  5. Rudolf Virchow states cells come from pre-existing cells.
• Lab Scenario: Using a high-power objective ($40 \times$) with a standard ocular lens ($10 \times$) results in a total magnification of $400 \times$.