Microscopy

Essential Mechanical and Optical Parts: Per the Lab Manual (page 51), the following components are critical for identifying and operating the compound light microscope:
- Ocular lens: The eyepiece through which the user views the specimen.
- Revolving nosepiece: The rotating part that holds the objective lenses.
- Objective lenses: Usually three lenses of varying magnification powers.
- Stage: The flat platform where the slide is placed for observation.
- Mechanical stage and Mechanical stage controls: Mechanisms used to hold the slide in place and move it precisely during viewing.
- Condenser with iris diaphragm: Focuses light onto the specimen and controls the amount of light passing through.
- Light: The illumination source at the base.
- Base: The bottom support of the microscope.
- Arm: The vertical support connecting the base to the head.
- Coarse focus: Used for initial focusing at low power.
- Fine focus: Used for precision focusing, especially at higher magnifications.
- Light switch: Turns the illumination source on and off.
- Light intensity: Control that adjusts the brightness of the light source.

Total Magnification Calculation: To determine the total magnification of the specimen being viewed, the following formula is applied: $\text{Total Magnification} = \text{Ocular lens} \times \text{Objective lens}$
Parfocal Capability: This term refers to the quality of a microscope that allows the specimen to stay in rough focus even when the magnification is changed (e.g., switching from a low-power objective to a high-power objective).
Maintenance and Cleaning:
- Lens Paper Only: It is mandatory to use lens paper exclusively for cleaning the optical glass surfaces to prevent scratching.
Inverse Relationships in Microscopy: As magnification increases, there is a corresponding decrease in the following parameters:
- Light intensity: The image becomes darker as the field of view narrows.
- Field-of-view: The actual diameter of the area of the slide that is visible.
- Depth-of-focus: The thickness of the specimen that remains in focus at one time.
- Working distance: Defined as the physical space between the microscope slide and the tip of the objective lens.

Working Distance Specifics:
- The working distance is greatest when using the low-power objective.
- The working distance is smallest when using the high-power objective.
- Safety Warning: Do NOT use the coarse focus knob while the microscope is set to high power, as this may drive the objective lens into the slide, potentially damaging both.
Step-by-Step Focusing Protocol:
1. Refer to the Lab Manual for specific guidelines.
2. Always begin focusing at low power using the coarse focus knob.
3. Center the specimen within the field-of-view before increasing magnification.
4. Increase magnification as necessary by rotating the nosepiece.
5. Adjust the light accordingly through three available methods (light intensity dial, iris diaphragm, or condenser height).
6. At high power, use the fine focus knob only to sharpen the image.

Storage Preparation:
1. Remove the slide from the stage.
2. Set the revolving nosepiece to the lowest magnification objective.
3. Wrap the power cord around the hand and then place it neatly on the stage.
4. Raise the stage all the way up.
5. Cover the instrument with its designated dust cover.
6. Return the microscope to the proper shelf, ensuring it is placed according to its assigned number.

Components of the Cell Cycle: The cell cycle consists of two major phases:
- Interphase: A period when the cell grows and performs all of its normal metabolic functions. It is subdivided into three phases:
  - $G_1$ : Gap phase 1.
  - $S$ : Synthesis phase (DNA replication occurs).
  - $G_2$ : Gap phase 2.
- Mitosis: The process of cell division.
Genetic Structure:
- Homologous Pair of Chromosomes: Consists of two chromosomes, one inherited from each parent (typically represented as red and blue pairs).
- Sister Chromatids: Identical copies produced by DNA replication, bound together to form the familiar "X" shape.
Cell Division Oversight: The process of cell division involves the separation of identical genetic material into two new nuclei, followed immediately by Cytokinesis, which is the division of the cytoplasm.
Checkpoints and Control Molecules: The progression through the cell cycle is determined by control molecules such as:
- Cyclins
- Cyclin-dependent kinases (CDKs)
- These molecules evaluate whether the cell is sufficiently prepared to transition to the next stage.

Stem Cells: These cells possess the unique capacity to differentiate into specialized cells, making them valuable for therapeutic applications aimed at replacing damaged body tissues.
Hematopoiesis: The biological process by which multipotent hematopoietic stem cells differentiate into various blood and immune cell types, including red blood cells and immune system cells.

Fish Blastula ( $100 \times$ ): A specimen used to observe various stages of the cell cycle.
Interphase ( $400 \times$ ): The stage where the cell is preparing for division but chromosomes are not yet visible as distinct structures.
Prophase ( $400 \times$ ): Chromosomes become coiled and visible but remain randomly arranged in the cell. The nuclear envelope has disappeared.
Metaphase ( $400 \times$ ): Chromosomes align along the center of the cell at the metaphase plate.
Anaphase ( $400 \times$ ): Sister chromatids separate and begin moving toward opposite poles of the cell.
- Newt Lung Cell Example: Fluorescence staining shows green mitotic spindles, red cell membrane/cytoplasm, and light blue chromosomes in anaphase.
Telophase ( $400 \times$ ): Characterized by the appearance of a cleavage furrow, indicating the beginning of physical separation of the two cells.
Daughter Cells ( $400 \times$ ): The result of cell division, where two separate cells return to Interphase correctly.