Microscopy and Biological Macromolecules: Study Notes

Microscopy in Biology

Introduction to Microscopy

Microscopes are essential tools in biological research and teaching laboratories, allowing scientists to observe structures too small to be seen with the naked eye. The two main types of microscopes used are optical microscopes and electron microscopes.

• Optical Microscopes: Use visible light and a series of lenses to magnify specimens. Examples include stereo microscopes, compound microscopes, and confocal microscopes.

• Electron Microscopes: Use beams of electrons for imaging, providing much higher resolution (up to 0.002 μm). There are two main types: transmission electron microscopes (TEM) and scanning electron microscopes (SEM).

Example: A compound microscope is commonly used in teaching labs to view thin tissue sections or single cells.

Major Types of Microscopes

The following table summarizes the main types of microscopes, their magnification, method of visualization, and common uses.

Type	Magnification	Method of Visualization	Common Uses
Stereo	10x–40x	Visible light, two optical paths	Dissecting, viewing large specimens
Compound	40x–1000x	Visible light, multiple lenses	Cells, thin tissue sections
Confocal	Up to 2000x	Laser scanning, optical sectioning	3D imaging of cells/tissues
Transmission Electron (TEM)	Up to 1,000,000x	Electron beam through specimen	Internal cell structures
Scanning Electron (SEM)	Up to 500,000x	Electron beam scans surface	Surface details of specimens

Compound Microscopes

Compound microscopes use two sets of lenses: the objective lens (closest to the specimen) and the ocular lens (eyepiece). The total magnification is the product of the magnifications of these two lenses.

• Total Magnification Formula:

$\text{Total Magnification} = \text{Ocular Magnification} \times \text{Objective Magnification}$

• Example: If the ocular lens is 15x and the objective lens is 40x, then $15 \times 40 = 600$.

The following table shows common combinations:

Ocular Magnification	Objective Magnification	Total Magnification
10x	4x	40x
10x	10x	100x
10x	40x	400x
15x	40x	600x
10x	100x	1000x

Field of View (FOV) and Depth of Field

The field of view (FOV) is the diameter of the visible area when looking through the microscope. It is measured in millimeters (mm) for low power and micrometers (μm) for high power objectives.

• FOV Formula:

$\text{FOV} = \frac{\text{Field Number}}{\text{Total Magnification}}$

• Field of view decreases as magnification increases.

• Depth of field is the range in which the specimen remains in focus; it also decreases with higher magnification.

• Specimens are best viewed when thinly sectioned or flattened to fit within the shallow depth of field.

Example: If the field number is 18 mm and the total magnification is 400x, then $\text{FOV} = \frac{18}{400} = 0.045$ mm.

Wet Mount Slides and Staining

A wet mount is a slide preparation in which a specimen is suspended in a drop of water. This method allows for quick preparation and observation of living specimens without drying or curing.

• Cover slips are used to flatten and secure the specimen.

• Lugol's iodine (IKI) is a common stain that turns black in the presence of starch, helping to visualize cellular structures.

Example: Lugol's iodine is used to stain potato cells to observe starch granules.

Biological Macromolecules

Functional Groups in Biological Molecules

Functional groups are specific groups of atoms within molecules that have characteristic properties and chemical reactivity. They are critical in determining the behavior of biological molecules.

Functional Group	Structure	Properties	Example Compound
Hydroxyl	–OH	Polar, forms hydrogen bonds	Ethanol
Carbonyl	–C=O	Polar, found in sugars	Acetone (ketone), Propanal (aldehyde)
Carboxyl	–COOH	Acidic, donates H+	Acetic acid
Amino	–NH2	Basic, accepts H+	Glycine
Sulfhydryl	–SH	Forms disulfide bonds	Cysteine
Phosphate	–PO42–	Contributes negative charge, energy transfer	Glycerol phosphate
Methyl	–CH3	Nonpolar, affects gene expression	5-methylcytosine

Classes of Biological Molecules

Biological macromolecules are large molecules essential for life. Most are polymers, made from repeating monomer units, except for lipids.

• Carbohydrates: Serve as energy sources and provide structural support. Monomer: monosaccharide (e.g., glucose). Polymer: polysaccharide (e.g., starch).

• Proteins: Perform a wide range of functions, including catalysis (enzymes), transport, and structural roles. Monomer: amino acid. Polymer: polypeptide or protein.

• Nucleic Acids: Store and transmit genetic information. Monomer: nucleotide. Polymer: DNA or RNA.

• Lipids: Diverse group not considered true polymers. Functions include energy storage, membrane structure, and signaling. Example: phospholipid.

Example: DNA is a nucleic acid polymer composed of nucleotide monomers; starch is a carbohydrate polymer made of glucose monomers.

Comparison of Biological Macromolecules

Class	Monomer	Polymer	Main Function	Example
Carbohydrates	Monosaccharide	Polysaccharide	Energy, structure	Starch, cellulose
Proteins	Amino acid	Polypeptide	Catalysis, structure, transport	Enzymes, hemoglobin
Nucleic Acids	Nucleotide	DNA, RNA	Genetic information	DNA, RNA
Lipids	Glycerol, fatty acids	Not true polymers	Membranes, energy storage	Phospholipids, triglycerides

Additional info: Lipids are grouped with macromolecules due to their biological importance, even though they are not polymers. The depth of field and field of view are critical concepts for accurate microscopy measurements and specimen analysis.